[v2,1/4] drm: Add helper for DP++ adaptors

Commit Message

Ville Syrjälä May 2, 2016, 7:08 p.m. UTC

From: Ville Syrjälä <[e-mail]>

Add a helper which aids in the identification of DP dual mode
(aka. DP++) adaptors. There are several types of adaptors
specified: type 1 DVI, type 1 HDMI, type 2 DVI, type 2 HDMI

Type 1 adaptors have a max TMDS clock limit of 165MHz, type 2 adaptors
may go as high as 300MHz and they provide a register informing the
source device what the actual limit is. Supposedly also type 1 adaptors
may optionally implement this register. This TMDS clock limit is the
main reason why we need to identify these adaptors.

Type 1 adaptors provide access to their internal registers and the sink
DDC bus through I2C. Type 2 adaptors provide this access both via I2C
and I2C-over-AUX. A type 2 source device may choose to implement either
of these methods. If a source device implements the I2C-over-AUX
method, then the driver will obviously need specific support for such
adaptors since the port is driven like an HDMI port, but DDC
communication happes over the AUX channel.

This helper should be enough to identify the adaptor type (some
type 1 DVI adaptors may be a slight exception) and the maximum TMDS
clock limit. Another feature that may be available is control over
the TMDS output buffers on the adaptor, possibly allowing for some
power saving when the TMDS link is down.

Other user controllable features that may be available in the adaptors
are downstream i2c bus speed control when using i2c-over-aux, and
some control over the CEC pin. I chose not to provide any helper
functions for those since I have no use for them in i915 at this time.
The rest of the registers in the adaptor are mostly just information,
eg. IEEE OUI, hardware and firmware revision, etc.

v2: Pass adaptor type to helper functions to ease driver implementation
    Fix a bunch of typoes (Paulo)
    Add DRM_DP_DUAL_MODE_UNKNOWN for the case where we don't (yet) know
    the type (Paulo)
    Reject 0x00 and 0xff DP_DUAL_MODE_MAX_TMDS_CLOCK values (Paulo)
    Adjust drm_dp_dual_mode_detect() type2 vs. type1 detection to
    ease future LSPCON enabling
    Remove the unused DP_DUAL_MODE_LAST_RESERVED define

Cc: [e-mail]
Cc: Tore Anderson <[e-mail]>
Cc: Paulo Zanoni <[e-mail]>
Cc: Shashank Sharma <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Signed-off-by: Ville Syrjälä <[e-mail]>
---
 drivers/gpu/drm/Makefile                  |   2 +-
 drivers/gpu/drm/drm_dp_dual_mode_helper.c | 356 ++++++++++++++++++++++++++++++
 include/drm/drm_dp_dual_mode_helper.h     |  83 +++++++
 3 files changed, 440 insertions(+), 1 deletion(-)
 create mode 100644 drivers/gpu/drm/drm_dp_dual_mode_helper.c
 create mode 100644 include/drm/drm_dp_dual_mode_helper.h

Comments

Jani Nikula May 3, 2016, 7:46 a.m. UTC | #1

On Mon, 02 May 2016, [e-mail] wrote:
> From: Ville Syrjälä <[e-mail]>
>
> Add a helper which aids in the identification of DP dual mode
> (aka. DP++) adaptors. There are several types of adaptors
> specified: type 1 DVI, type 1 HDMI, type 2 DVI, type 2 HDMI
>
> Type 1 adaptors have a max TMDS clock limit of 165MHz, type 2 adaptors
> may go as high as 300MHz and they provide a register informing the
> source device what the actual limit is. Supposedly also type 1 adaptors
> may optionally implement this register. This TMDS clock limit is the
> main reason why we need to identify these adaptors.
>
> Type 1 adaptors provide access to their internal registers and the sink
> DDC bus through I2C. Type 2 adaptors provide this access both via I2C
> and I2C-over-AUX. A type 2 source device may choose to implement either
> of these methods. If a source device implements the I2C-over-AUX
> method, then the driver will obviously need specific support for such
> adaptors since the port is driven like an HDMI port, but DDC
> communication happes over the AUX channel.
>
> This helper should be enough to identify the adaptor type (some
> type 1 DVI adaptors may be a slight exception) and the maximum TMDS
> clock limit. Another feature that may be available is control over
> the TMDS output buffers on the adaptor, possibly allowing for some
> power saving when the TMDS link is down.
>
> Other user controllable features that may be available in the adaptors
> are downstream i2c bus speed control when using i2c-over-aux, and
> some control over the CEC pin. I chose not to provide any helper
> functions for those since I have no use for them in i915 at this time.
> The rest of the registers in the adaptor are mostly just information,
> eg. IEEE OUI, hardware and firmware revision, etc.
>
> v2: Pass adaptor type to helper functions to ease driver implementation
>     Fix a bunch of typoes (Paulo)
>     Add DRM_DP_DUAL_MODE_UNKNOWN for the case where we don't (yet) know
>     the type (Paulo)
>     Reject 0x00 and 0xff DP_DUAL_MODE_MAX_TMDS_CLOCK values (Paulo)
>     Adjust drm_dp_dual_mode_detect() type2 vs. type1 detection to
>     ease future LSPCON enabling
>     Remove the unused DP_DUAL_MODE_LAST_RESERVED define
>
> Cc: [e-mail]
> Cc: Tore Anderson <[e-mail]>
> Cc: Paulo Zanoni <[e-mail]>
> Cc: Shashank Sharma <[e-mail]>
> Cc: Daniel Vetter <[e-mail]>
> Signed-off-by: Ville Syrjälä <[e-mail]>
> ---
>  drivers/gpu/drm/Makefile                  |   2 +-
>  drivers/gpu/drm/drm_dp_dual_mode_helper.c | 356 ++++++++++++++++++++++++++++++
>  include/drm/drm_dp_dual_mode_helper.h     |  83 +++++++
>  3 files changed, 440 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/gpu/drm/drm_dp_dual_mode_helper.c
>  create mode 100644 include/drm/drm_dp_dual_mode_helper.h
>
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index 1a26b4eb1ce0..29f2ee9b9534 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -23,7 +23,7 @@ drm-$(CONFIG_AGP) += drm_agpsupport.o
>  
>  drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
>  		drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o \
> -		drm_kms_helper_common.o
> +		drm_kms_helper_common.o drm_dp_dual_mode_helper.o
>  
>  drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
>  drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
> diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> new file mode 100644
> index 000000000000..949c0fbeb542
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> @@ -0,0 +1,356 @@
> +/*
> + * Copyright © 2016 Intel Corporation
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the "Software"),
> + * to deal in the Software without restriction, including without limitation
> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> + * OTHER DEALINGS IN THE SOFTWARE.
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/export.h>
> +#include <linux/i2c.h>
> +#include <linux/slab.h>
> +#include <linux/string.h>
> +#include <drm/drm_dp_dual_mode_helper.h>
> +#include <drm/drmP.h>
> +
> +/**
> + * DOC: DP dual mode (aka. DP++) adaptor helpers
> + *
> + * Helper functions to deal with DP dual mode adaptors.
> + *
> + * Type 1:
> + * Adaptor registers (if any) and the sink DDC bus may be accessed via I2C.
> + *
> + * Type 2:
> + * Adaptor registers and sink DDC bus can be accessed either via I2C or
> + * I2C-over-AUX. Source devices may choose to implement either of these
> + * access methods.
> + */
> +
> +#define DP_DUAL_MODE_SLAVE_ADDRESS 0x40
> +
> +/**
> + * drm_dp_dual_mode_read - Read from the DP dual mode adaptor register(s)
> + * adapter: I2C adapter for the DDC bus
> + * offset: register offset
> + * buffer: buffer for return data
> + * size: sizo of the buffer

The parameters need to be prefixed with @ in kernel-doc. Same across the
patch series.

BR,
Jani.


> + *
> + * Reads @size bytes from the DP dual mode adaptor registers
> + * starting at @offset.
> + *
> + * Returns:
> + * 0 on success, negative error code on failure
> + */
> +ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
> +			      u8 offset, void *buffer, size_t size)
> +{
> +	struct i2c_msg msgs[] = {
> +		{
> +			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> +			.flags = 0,
> +			.len = 1,
> +			.buf = &offset,
> +		},
> +		{
> +			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> +			.flags = I2C_M_RD,
> +			.len = size,
> +			.buf = buffer,
> +		},
> +	};
> +	int ret;
> +
> +	ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
> +	if (ret < 0)
> +		return ret;
> +	if (ret != ARRAY_SIZE(msgs))
> +		return -EPROTO;
> +
> +	return 0;
> +}
> +
> +/**
> + * drm_dp_dual_mode_write - Write to the DP dual mode adaptor register(s)
> + * adapter: I2C adapter for the DDC bus
> + * offset: register offset
> + * buffer: buffer for write data
> + * size: sizo of the buffer
> + *
> + * Writes @size bytes to the DP dual mode adaptor registers
> + * starting at @offset.
> + *
> + * Returns:
> + * 0 on success, negative error code on failure
> + */
> +ssize_t drm_dp_dual_mode_write(struct i2c_adapter *adapter,
> +			       u8 offset, const void *buffer, size_t size)
> +{
> +	struct i2c_msg msg = {
> +		.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> +		.flags = 0,
> +		.len = 1 + size,
> +		.buf = NULL,
> +	};
> +	void *data;
> +	int ret;
> +
> +	data = kmalloc(msg.len, GFP_TEMPORARY);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	msg.buf = data;
> +
> +	memcpy(data, &offset, 1);
> +	memcpy(data + 1, buffer, size);
> +
> +	ret = i2c_transfer(adapter, &msg, 1);
> +
> +	kfree(data);
> +
> +	if (ret < 0)
> +		return ret;
> +	if (ret != 1)
> +		return -EPROTO;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_dual_mode_write);
> +
> +static bool is_hdmi_adaptor(const char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN])
> +{
> +	static const char dp_dual_mode_hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] =
> +		"DP-HDMI ADAPTOR\x04";
> +
> +	return memcmp(hdmi_id, dp_dual_mode_hdmi_id,
> +		      sizeof(dp_dual_mode_hdmi_id)) == 0;
> +}
> +
> +static bool is_type2_adaptor(uint8_t adaptor_id)
> +{
> +	return adaptor_id == (DP_DUAL_MODE_TYPE_TYPE2 |
> +			      DP_DUAL_MODE_REV_TYPE2);
> +}
> +
> +/**
> + * drm_dp_dual_mode_detect - Identify the DP dual mode adaptor
> + * adapter: I2C adapter for the DDC bus
> + *
> + * Attempt to identify the type of the DP dual mode adaptor used.
> + *
> + * Note that when the answer is @DRM_DP_DUAL_MODE_NONE it's not
> + * certain whether we're dealing with a native HDMI port or
> + * a type 1 DVI dual mode adaptor. The driver will have to use
> + * some other hardware/driver specific mechanism to make that
> + * distinction.
> + *
> + * Returns:
> + * The type of the DP dual mode adaptor used
> + */
> +enum drm_dp_dual_mode_type drm_dp_dual_mode_detect(struct i2c_adapter *adapter)
> +{
> +	char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] = {};
> +	uint8_t adaptor_id = 0x00;
> +	ssize_t ret;
> +
> +	/*
> +	 * Let's see if the adaptor is there the by reading the
> +	 * HDMI ID registers.
> +	 *
> +	 * Note that type 1 DVI adaptors are not required to implemnt
> +	 * any registers, and that presents a problem for detection.
> +	 * If the i2c transfer is nacked, we may or may not be dealing
> +	 * with a type 1 DVI adaptor. Some other mechanism of detecting
> +	 * the presence of the adaptor is required. One way would be
> +	 * to check the state of the CONFIG1 pin, Another method would
> +	 * simply require the driver to know whether the port is a DP++
> +	 * port or a native HDMI port. Both of these methods are entirely
> +	 * hardware/driver specific so we can't deal with them here.
> +	 */
> +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_HDMI_ID,
> +				    hdmi_id, sizeof(hdmi_id));
> +	if (ret)
> +		return DRM_DP_DUAL_MODE_UNKNOWN;
> +
> +	/*
> +	 * Sigh. Some (maybe all?) type 1 adaptors are broken and ack
> +	 * the offset but ignore it, and instead they just always return
> +	 * data from the start of the HDMI ID buffer. So for a broken
> +	 * type 1 HDMI adaptor a single byte read will always give us
> +	 * 0x44, and for a type 1 DVI adaptor it should give 0x00
> +	 * (assuming it implements any registers). Fortunately neither
> +	 * of those values will match the type 2 signature of the
> +	 * DP_DUAL_MODE_ADAPTOR_ID register so we can proceed with
> +	 * the type 2 adaptor detection safely even in the presence
> +	 * of broken type 1 adaptors.
> +	 */
> +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_ADAPTOR_ID,
> +				    &adaptor_id, sizeof(adaptor_id));
> +	if (ret == 0) {
> +		if (is_type2_adaptor(adaptor_id) && is_hdmi_adaptor(hdmi_id))
> +			return DRM_DP_DUAL_MODE_TYPE2_HDMI;
> +		else if (is_type2_adaptor(adaptor_id))
> +			return DRM_DP_DUAL_MODE_TYPE2_DVI;
> +	}
> +
> +	if (is_hdmi_adaptor(hdmi_id))
> +		return DRM_DP_DUAL_MODE_TYPE1_HDMI;
> +	else
> +		return DRM_DP_DUAL_MODE_TYPE1_DVI;
> +}
> +EXPORT_SYMBOL(drm_dp_dual_mode_detect);
> +
> +/**
> + * drm_dp_dual_mode_max_tmds_clock - Max TMDS clock for DP dual mode adaptor
> + * type: DP dual mode adaptor type
> + * adapter: I2C adapter for the DDC bus
> + *
> + * Determine the max TMDS clock the adaptor supports based on the
> + * type of the dual mode adaptor and the DP_DUAL_MODE_MAX_TMDS_CLOCK
> + * register (on type2 adaptors). As some type 1 adaptors have
> + * problems with registers (see comments in drm_dp_dual_mode_detect())
> + * we don't read the register on those, instead we simply assume
> + * a 165 MHz limit based on the specification.
> + *
> + * Returns:
> + * Maximum supported TMDS clock rate for the DP dual mode adaptor in kHz.
> + */
> +int drm_dp_dual_mode_max_tmds_clock(enum drm_dp_dual_mode_type type,
> +				    struct i2c_adapter *adapter)
> +{
> +	uint8_t max_tmds_clock;
> +	ssize_t ret;
> +
> +	/* native HDMI so no limit */
> +	if (type == DRM_DP_DUAL_MODE_NONE)
> +		return 0;
> +
> +	/*
> +	 * Type 1 adaptors are limited to 165MHz
> +	 * Type 2 adaptors can tells us their limit
> +	 */
> +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
> +		return 165000;
> +
> +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_MAX_TMDS_CLOCK,
> +				    &max_tmds_clock, sizeof(max_tmds_clock));
> +	if (ret || max_tmds_clock == 0x00 || max_tmds_clock == 0xff)
> +		return 165000;
> +
> +	return max_tmds_clock * 5000 / 2;
> +}
> +EXPORT_SYMBOL(drm_dp_dual_mode_max_tmds_clock);
> +
> +/**
> + * drm_dp_dual_mode_get_tmds_output - Get the state of the TMDS output buffers in the DP dual mode adaptor
> + * type: DP dual mode adaptor type
> + * adapter: I2C adapter for the DDC bus
> + * enabled: current state of the TMDS output buffers
> + *
> + * Get the state of the TMDS output buffers in the adaptor. For
> + * type2 adaptors this is queried from the DP_DUAL_MODE_TMDS_OEN
> + * register. As some type 1 adaptors have problems with registers
> + * (see comments in drm_dp_dual_mode_detect()) we don't read the
> + * register on those, instead we simply assume that the buffers
> + * are always enabled.
> + *
> + * Returns:
> + * 0 on success, negative error code on failure
> + */
> +int drm_dp_dual_mode_get_tmds_output(enum drm_dp_dual_mode_type type,
> +				     struct i2c_adapter *adapter,
> +				     bool *enabled)
> +{
> +	uint8_t tmds_oen;
> +	ssize_t ret;
> +
> +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI) {
> +		*enabled = true;
> +		return 0;
> +	}
> +
> +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_TMDS_OEN,
> +				    &tmds_oen, sizeof(tmds_oen));
> +	if (ret)
> +		return ret;
> +
> +	*enabled = !(tmds_oen & DP_DUAL_MODE_TMDS_DISABLE);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_dual_mode_get_tmds_output);
> +
> +/**
> + * drm_dp_dual_mode_set_tmds_output - Enable/disable TMDS output buffers in the DP dual mode adaptor
> + * type: DP dual mode adaptor type
> + * adapter: I2C adapter for the DDC bus
> + * enable: enable (as opposed to disable) the TMDS output buffers
> + *
> + * Set the state of the TMDS output buffers in the adaptor. For
> + * type2 this is set via the DP_DUAL_MODE_TMDS_OEN register. As
> + * some type 1 adaptors have problems with registers (see comments
> + * in drm_dp_dual_mode_detect()) we avoid touching the register,
> + * making this function a no-op on type 1 adaptors.
> + *
> + * Returns:
> + * 0 on success, negative error code on failure
> + */
> +int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type,
> +				     struct i2c_adapter *adapter, bool enable)
> +{
> +	uint8_t tmds_oen = enable ? 0 : DP_DUAL_MODE_TMDS_DISABLE;
> +	ssize_t ret;
> +
> +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
> +		return 0;
> +
> +	ret = drm_dp_dual_mode_write(adapter, DP_DUAL_MODE_TMDS_OEN,
> +				     &tmds_oen, sizeof(tmds_oen));
> +	if (ret)
> +		return ret;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_dual_mode_set_tmds_output);
> +
> +/**
> + * drm_dp_get_dual_mode_type_name - Get the name of the DP dual mode adaptor type as a string
> + * type: DP dual mode adaptor type
> + *
> + * Returns:
> + * String representation of the DP dual mode adaptor type
> + */
> +const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type)
> +{
> +	switch (type) {
> +	case DRM_DP_DUAL_MODE_NONE:
> +		return "none";
> +	case DRM_DP_DUAL_MODE_TYPE1_DVI:
> +		return "type 1 DVI";
> +	case DRM_DP_DUAL_MODE_TYPE1_HDMI:
> +		return "type 1 HDMI";
> +	case DRM_DP_DUAL_MODE_TYPE2_DVI:
> +		return "type 2 DVI";
> +	case DRM_DP_DUAL_MODE_TYPE2_HDMI:
> +		return "type 2 HDMI";
> +	default:
> +		WARN_ON(type != DRM_DP_DUAL_MODE_UNKNOWN);
> +		return "unknown";
> +	}
> +}
> +EXPORT_SYMBOL(drm_dp_get_dual_mode_type_name);
> diff --git a/include/drm/drm_dp_dual_mode_helper.h b/include/drm/drm_dp_dual_mode_helper.h
> new file mode 100644
> index 000000000000..b4603b9fc03d
> --- /dev/null
> +++ b/include/drm/drm_dp_dual_mode_helper.h
> @@ -0,0 +1,83 @@
> +/*
> + * Copyright © 2016 Intel Corporation
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the "Software"),
> + * to deal in the Software without restriction, including without limitation
> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> + * OTHER DEALINGS IN THE SOFTWARE.
> + */
> +
> +#ifndef DRM_DP_DUAL_MODE_HELPER_H
> +#define DRM_DP_DUAL_MODE_HELPER_H
> +
> +#include <linux/types.h>
> +
> +/*
> + * Optional for type 1 DVI adaptors
> + * Mandatory for type 1 HDMI and type 2 adators
> + */
> +#define DP_DUAL_MODE_HDMI_ID 0x00 /* 00-0f */
> +#define  DP_DUAL_MODE_HDMI_ID_LEN 16
> +/*
> + * Optional for type 1 adaptors
> + * Mandatory for type 2 adators
> + */
> +#define DP_DUAL_MODE_ADAPTOR_ID 0x10
> +#define  DP_DUAL_MODE_REV_MASK 0x07
> +#define  DP_DUAL_MODE_REV_TYPE2 0x00
> +#define  DP_DUAL_MODE_TYPE_MASK 0xf0
> +#define  DP_DUAL_MODE_TYPE_TYPE2 0xa0
> +#define DP_DUAL_MODE_IEEE_OUI 0x11 /* 11-13*/
> +#define  DP_DUAL_IEEE_OUI_LEN 3
> +#define DP_DUAL_DEVICE_ID 0x14 /* 14-19 */
> +#define  DP_DUAL_DEVICE_ID_LEN 6
> +#define DP_DUAL_MODE_HARDWARE_REV 0x1a
> +#define DP_DUAL_MODE_FIRMWARE_MAJOR_REV 0x1b
> +#define DP_DUAL_MODE_FIRMWARE_MINOR_REV 0x1c
> +#define DP_DUAL_MODE_MAX_TMDS_CLOCK 0x1d
> +#define DP_DUAL_MODE_I2C_SPEED_CAP 0x1e
> +#define DP_DUAL_MODE_TMDS_OEN 0x20
> +#define  DP_DUAL_MODE_TMDS_DISABLE 0x01
> +#define DP_DUAL_MODE_HDMI_PIN_CTRL 0x21
> +#define  DP_DUAL_MODE_CEC_ENABLE 0x01
> +#define DP_DUAL_MODE_I2C_SPEED_CTRL 0x22
> +
> +struct i2c_adapter;
> +
> +ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
> +			      u8 offset, void *buffer, size_t size);
> +ssize_t drm_dp_dual_mode_write(struct i2c_adapter *adapter,
> +			       u8 offset, const void *buffer, size_t size);
> +
> +enum drm_dp_dual_mode_type {
> +	DRM_DP_DUAL_MODE_NONE,
> +	DRM_DP_DUAL_MODE_UNKNOWN,
> +	DRM_DP_DUAL_MODE_TYPE1_DVI,
> +	DRM_DP_DUAL_MODE_TYPE1_HDMI,
> +	DRM_DP_DUAL_MODE_TYPE2_DVI,
> +	DRM_DP_DUAL_MODE_TYPE2_HDMI,
> +};
> +
> +enum drm_dp_dual_mode_type drm_dp_dual_mode_detect(struct i2c_adapter *adapter);
> +int drm_dp_dual_mode_max_tmds_clock(enum drm_dp_dual_mode_type type,
> +				    struct i2c_adapter *adapter);
> +int drm_dp_dual_mode_get_tmds_output(enum drm_dp_dual_mode_type type,
> +				     struct i2c_adapter *adapter, bool *enabled);
> +int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type,
> +				     struct i2c_adapter *adapter, bool enable);
> +const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type);
> +
> +#endif

Ville Syrjälä May 3, 2016, 1:38 p.m. UTC | #2

On Tue, May 03, 2016 at 10:46:26AM +0300, Jani Nikula wrote:
> On Mon, 02 May 2016, [e-mail] wrote:
> > From: Ville Syrjälä <[e-mail]>
> >
> > Add a helper which aids in the identification of DP dual mode
> > (aka. DP++) adaptors. There are several types of adaptors
> > specified: type 1 DVI, type 1 HDMI, type 2 DVI, type 2 HDMI
> >
> > Type 1 adaptors have a max TMDS clock limit of 165MHz, type 2 adaptors
> > may go as high as 300MHz and they provide a register informing the
> > source device what the actual limit is. Supposedly also type 1 adaptors
> > may optionally implement this register. This TMDS clock limit is the
> > main reason why we need to identify these adaptors.
> >
> > Type 1 adaptors provide access to their internal registers and the sink
> > DDC bus through I2C. Type 2 adaptors provide this access both via I2C
> > and I2C-over-AUX. A type 2 source device may choose to implement either
> > of these methods. If a source device implements the I2C-over-AUX
> > method, then the driver will obviously need specific support for such
> > adaptors since the port is driven like an HDMI port, but DDC
> > communication happes over the AUX channel.
> >
> > This helper should be enough to identify the adaptor type (some
> > type 1 DVI adaptors may be a slight exception) and the maximum TMDS
> > clock limit. Another feature that may be available is control over
> > the TMDS output buffers on the adaptor, possibly allowing for some
> > power saving when the TMDS link is down.
> >
> > Other user controllable features that may be available in the adaptors
> > are downstream i2c bus speed control when using i2c-over-aux, and
> > some control over the CEC pin. I chose not to provide any helper
> > functions for those since I have no use for them in i915 at this time.
> > The rest of the registers in the adaptor are mostly just information,
> > eg. IEEE OUI, hardware and firmware revision, etc.
> >
> > v2: Pass adaptor type to helper functions to ease driver implementation
> >     Fix a bunch of typoes (Paulo)
> >     Add DRM_DP_DUAL_MODE_UNKNOWN for the case where we don't (yet) know
> >     the type (Paulo)
> >     Reject 0x00 and 0xff DP_DUAL_MODE_MAX_TMDS_CLOCK values (Paulo)
> >     Adjust drm_dp_dual_mode_detect() type2 vs. type1 detection to
> >     ease future LSPCON enabling
> >     Remove the unused DP_DUAL_MODE_LAST_RESERVED define
> >
> > Cc: [e-mail]
> > Cc: Tore Anderson <[e-mail]>
> > Cc: Paulo Zanoni <[e-mail]>
> > Cc: Shashank Sharma <[e-mail]>
> > Cc: Daniel Vetter <[e-mail]>
> > Signed-off-by: Ville Syrjälä <[e-mail]>
> > ---
> >  drivers/gpu/drm/Makefile                  |   2 +-
> >  drivers/gpu/drm/drm_dp_dual_mode_helper.c | 356 ++++++++++++++++++++++++++++++
> >  include/drm/drm_dp_dual_mode_helper.h     |  83 +++++++
> >  3 files changed, 440 insertions(+), 1 deletion(-)
> >  create mode 100644 drivers/gpu/drm/drm_dp_dual_mode_helper.c
> >  create mode 100644 include/drm/drm_dp_dual_mode_helper.h
> >
> > diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> > index 1a26b4eb1ce0..29f2ee9b9534 100644
> > --- a/drivers/gpu/drm/Makefile
> > +++ b/drivers/gpu/drm/Makefile
> > @@ -23,7 +23,7 @@ drm-$(CONFIG_AGP) += drm_agpsupport.o
> >  
> >  drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
> >  		drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o \
> > -		drm_kms_helper_common.o
> > +		drm_kms_helper_common.o drm_dp_dual_mode_helper.o
> >  
> >  drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
> >  drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
> > diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> > new file mode 100644
> > index 000000000000..949c0fbeb542
> > --- /dev/null
> > +++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> > @@ -0,0 +1,356 @@
> > +/*
> > + * Copyright © 2016 Intel Corporation
> > + *
> > + * Permission is hereby granted, free of charge, to any person obtaining a
> > + * copy of this software and associated documentation files (the "Software"),
> > + * to deal in the Software without restriction, including without limitation
> > + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> > + * and/or sell copies of the Software, and to permit persons to whom the
> > + * Software is furnished to do so, subject to the following conditions:
> > + *
> > + * The above copyright notice and this permission notice shall be included in
> > + * all copies or substantial portions of the Software.
> > + *
> > + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> > + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> > + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> > + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> > + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> > + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> > + * OTHER DEALINGS IN THE SOFTWARE.
> > + */
> > +
> > +#include <linux/errno.h>
> > +#include <linux/export.h>
> > +#include <linux/i2c.h>
> > +#include <linux/slab.h>
> > +#include <linux/string.h>
> > +#include <drm/drm_dp_dual_mode_helper.h>
> > +#include <drm/drmP.h>
> > +
> > +/**
> > + * DOC: DP dual mode (aka. DP++) adaptor helpers
> > + *
> > + * Helper functions to deal with DP dual mode adaptors.
> > + *
> > + * Type 1:
> > + * Adaptor registers (if any) and the sink DDC bus may be accessed via I2C.
> > + *
> > + * Type 2:
> > + * Adaptor registers and sink DDC bus can be accessed either via I2C or
> > + * I2C-over-AUX. Source devices may choose to implement either of these
> > + * access methods.
> > + */
> > +
> > +#define DP_DUAL_MODE_SLAVE_ADDRESS 0x40
> > +
> > +/**
> > + * drm_dp_dual_mode_read - Read from the DP dual mode adaptor register(s)
> > + * adapter: I2C adapter for the DDC bus
> > + * offset: register offset
> > + * buffer: buffer for return data
> > + * size: sizo of the buffer
> 
> The parameters need to be prefixed with @ in kernel-doc. Same across the
> patch series.

Hmm. I guess kernel-doc is just too complicated for me. I never get
the magic formatting right. v3 coming up...

> 
> BR,
> Jani.
> 
> 
> > + *
> > + * Reads @size bytes from the DP dual mode adaptor registers
> > + * starting at @offset.
> > + *
> > + * Returns:
> > + * 0 on success, negative error code on failure
> > + */
> > +ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
> > +			      u8 offset, void *buffer, size_t size)
> > +{
> > +	struct i2c_msg msgs[] = {
> > +		{
> > +			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> > +			.flags = 0,
> > +			.len = 1,
> > +			.buf = &offset,
> > +		},
> > +		{
> > +			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> > +			.flags = I2C_M_RD,
> > +			.len = size,
> > +			.buf = buffer,
> > +		},
> > +	};
> > +	int ret;
> > +
> > +	ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
> > +	if (ret < 0)
> > +		return ret;
> > +	if (ret != ARRAY_SIZE(msgs))
> > +		return -EPROTO;
> > +
> > +	return 0;
> > +}
> > +
> > +/**
> > + * drm_dp_dual_mode_write - Write to the DP dual mode adaptor register(s)
> > + * adapter: I2C adapter for the DDC bus
> > + * offset: register offset
> > + * buffer: buffer for write data
> > + * size: sizo of the buffer
> > + *
> > + * Writes @size bytes to the DP dual mode adaptor registers
> > + * starting at @offset.
> > + *
> > + * Returns:
> > + * 0 on success, negative error code on failure
> > + */
> > +ssize_t drm_dp_dual_mode_write(struct i2c_adapter *adapter,
> > +			       u8 offset, const void *buffer, size_t size)
> > +{
> > +	struct i2c_msg msg = {
> > +		.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> > +		.flags = 0,
> > +		.len = 1 + size,
> > +		.buf = NULL,
> > +	};
> > +	void *data;
> > +	int ret;
> > +
> > +	data = kmalloc(msg.len, GFP_TEMPORARY);
> > +	if (!data)
> > +		return -ENOMEM;
> > +
> > +	msg.buf = data;
> > +
> > +	memcpy(data, &offset, 1);
> > +	memcpy(data + 1, buffer, size);
> > +
> > +	ret = i2c_transfer(adapter, &msg, 1);
> > +
> > +	kfree(data);
> > +
> > +	if (ret < 0)
> > +		return ret;
> > +	if (ret != 1)
> > +		return -EPROTO;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_dp_dual_mode_write);
> > +
> > +static bool is_hdmi_adaptor(const char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN])
> > +{
> > +	static const char dp_dual_mode_hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] =
> > +		"DP-HDMI ADAPTOR\x04";
> > +
> > +	return memcmp(hdmi_id, dp_dual_mode_hdmi_id,
> > +		      sizeof(dp_dual_mode_hdmi_id)) == 0;
> > +}
> > +
> > +static bool is_type2_adaptor(uint8_t adaptor_id)
> > +{
> > +	return adaptor_id == (DP_DUAL_MODE_TYPE_TYPE2 |
> > +			      DP_DUAL_MODE_REV_TYPE2);
> > +}
> > +
> > +/**
> > + * drm_dp_dual_mode_detect - Identify the DP dual mode adaptor
> > + * adapter: I2C adapter for the DDC bus
> > + *
> > + * Attempt to identify the type of the DP dual mode adaptor used.
> > + *
> > + * Note that when the answer is @DRM_DP_DUAL_MODE_NONE it's not
> > + * certain whether we're dealing with a native HDMI port or
> > + * a type 1 DVI dual mode adaptor. The driver will have to use
> > + * some other hardware/driver specific mechanism to make that
> > + * distinction.
> > + *
> > + * Returns:
> > + * The type of the DP dual mode adaptor used
> > + */
> > +enum drm_dp_dual_mode_type drm_dp_dual_mode_detect(struct i2c_adapter *adapter)
> > +{
> > +	char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] = {};
> > +	uint8_t adaptor_id = 0x00;
> > +	ssize_t ret;
> > +
> > +	/*
> > +	 * Let's see if the adaptor is there the by reading the
> > +	 * HDMI ID registers.
> > +	 *
> > +	 * Note that type 1 DVI adaptors are not required to implemnt
> > +	 * any registers, and that presents a problem for detection.
> > +	 * If the i2c transfer is nacked, we may or may not be dealing
> > +	 * with a type 1 DVI adaptor. Some other mechanism of detecting
> > +	 * the presence of the adaptor is required. One way would be
> > +	 * to check the state of the CONFIG1 pin, Another method would
> > +	 * simply require the driver to know whether the port is a DP++
> > +	 * port or a native HDMI port. Both of these methods are entirely
> > +	 * hardware/driver specific so we can't deal with them here.
> > +	 */
> > +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_HDMI_ID,
> > +				    hdmi_id, sizeof(hdmi_id));
> > +	if (ret)
> > +		return DRM_DP_DUAL_MODE_UNKNOWN;
> > +
> > +	/*
> > +	 * Sigh. Some (maybe all?) type 1 adaptors are broken and ack
> > +	 * the offset but ignore it, and instead they just always return
> > +	 * data from the start of the HDMI ID buffer. So for a broken
> > +	 * type 1 HDMI adaptor a single byte read will always give us
> > +	 * 0x44, and for a type 1 DVI adaptor it should give 0x00
> > +	 * (assuming it implements any registers). Fortunately neither
> > +	 * of those values will match the type 2 signature of the
> > +	 * DP_DUAL_MODE_ADAPTOR_ID register so we can proceed with
> > +	 * the type 2 adaptor detection safely even in the presence
> > +	 * of broken type 1 adaptors.
> > +	 */
> > +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_ADAPTOR_ID,
> > +				    &adaptor_id, sizeof(adaptor_id));
> > +	if (ret == 0) {
> > +		if (is_type2_adaptor(adaptor_id) && is_hdmi_adaptor(hdmi_id))
> > +			return DRM_DP_DUAL_MODE_TYPE2_HDMI;
> > +		else if (is_type2_adaptor(adaptor_id))
> > +			return DRM_DP_DUAL_MODE_TYPE2_DVI;
> > +	}
> > +
> > +	if (is_hdmi_adaptor(hdmi_id))
> > +		return DRM_DP_DUAL_MODE_TYPE1_HDMI;
> > +	else
> > +		return DRM_DP_DUAL_MODE_TYPE1_DVI;
> > +}
> > +EXPORT_SYMBOL(drm_dp_dual_mode_detect);
> > +
> > +/**
> > + * drm_dp_dual_mode_max_tmds_clock - Max TMDS clock for DP dual mode adaptor
> > + * type: DP dual mode adaptor type
> > + * adapter: I2C adapter for the DDC bus
> > + *
> > + * Determine the max TMDS clock the adaptor supports based on the
> > + * type of the dual mode adaptor and the DP_DUAL_MODE_MAX_TMDS_CLOCK
> > + * register (on type2 adaptors). As some type 1 adaptors have
> > + * problems with registers (see comments in drm_dp_dual_mode_detect())
> > + * we don't read the register on those, instead we simply assume
> > + * a 165 MHz limit based on the specification.
> > + *
> > + * Returns:
> > + * Maximum supported TMDS clock rate for the DP dual mode adaptor in kHz.
> > + */
> > +int drm_dp_dual_mode_max_tmds_clock(enum drm_dp_dual_mode_type type,
> > +				    struct i2c_adapter *adapter)
> > +{
> > +	uint8_t max_tmds_clock;
> > +	ssize_t ret;
> > +
> > +	/* native HDMI so no limit */
> > +	if (type == DRM_DP_DUAL_MODE_NONE)
> > +		return 0;
> > +
> > +	/*
> > +	 * Type 1 adaptors are limited to 165MHz
> > +	 * Type 2 adaptors can tells us their limit
> > +	 */
> > +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
> > +		return 165000;
> > +
> > +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_MAX_TMDS_CLOCK,
> > +				    &max_tmds_clock, sizeof(max_tmds_clock));
> > +	if (ret || max_tmds_clock == 0x00 || max_tmds_clock == 0xff)
> > +		return 165000;
> > +
> > +	return max_tmds_clock * 5000 / 2;
> > +}
> > +EXPORT_SYMBOL(drm_dp_dual_mode_max_tmds_clock);
> > +
> > +/**
> > + * drm_dp_dual_mode_get_tmds_output - Get the state of the TMDS output buffers in the DP dual mode adaptor
> > + * type: DP dual mode adaptor type
> > + * adapter: I2C adapter for the DDC bus
> > + * enabled: current state of the TMDS output buffers
> > + *
> > + * Get the state of the TMDS output buffers in the adaptor. For
> > + * type2 adaptors this is queried from the DP_DUAL_MODE_TMDS_OEN
> > + * register. As some type 1 adaptors have problems with registers
> > + * (see comments in drm_dp_dual_mode_detect()) we don't read the
> > + * register on those, instead we simply assume that the buffers
> > + * are always enabled.
> > + *
> > + * Returns:
> > + * 0 on success, negative error code on failure
> > + */
> > +int drm_dp_dual_mode_get_tmds_output(enum drm_dp_dual_mode_type type,
> > +				     struct i2c_adapter *adapter,
> > +				     bool *enabled)
> > +{
> > +	uint8_t tmds_oen;
> > +	ssize_t ret;
> > +
> > +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI) {
> > +		*enabled = true;
> > +		return 0;
> > +	}
> > +
> > +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_TMDS_OEN,
> > +				    &tmds_oen, sizeof(tmds_oen));
> > +	if (ret)
> > +		return ret;
> > +
> > +	*enabled = !(tmds_oen & DP_DUAL_MODE_TMDS_DISABLE);
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_dp_dual_mode_get_tmds_output);
> > +
> > +/**
> > + * drm_dp_dual_mode_set_tmds_output - Enable/disable TMDS output buffers in the DP dual mode adaptor
> > + * type: DP dual mode adaptor type
> > + * adapter: I2C adapter for the DDC bus
> > + * enable: enable (as opposed to disable) the TMDS output buffers
> > + *
> > + * Set the state of the TMDS output buffers in the adaptor. For
> > + * type2 this is set via the DP_DUAL_MODE_TMDS_OEN register. As
> > + * some type 1 adaptors have problems with registers (see comments
> > + * in drm_dp_dual_mode_detect()) we avoid touching the register,
> > + * making this function a no-op on type 1 adaptors.
> > + *
> > + * Returns:
> > + * 0 on success, negative error code on failure
> > + */
> > +int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type,
> > +				     struct i2c_adapter *adapter, bool enable)
> > +{
> > +	uint8_t tmds_oen = enable ? 0 : DP_DUAL_MODE_TMDS_DISABLE;
> > +	ssize_t ret;
> > +
> > +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
> > +		return 0;
> > +
> > +	ret = drm_dp_dual_mode_write(adapter, DP_DUAL_MODE_TMDS_OEN,
> > +				     &tmds_oen, sizeof(tmds_oen));
> > +	if (ret)
> > +		return ret;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_dp_dual_mode_set_tmds_output);
> > +
> > +/**
> > + * drm_dp_get_dual_mode_type_name - Get the name of the DP dual mode adaptor type as a string
> > + * type: DP dual mode adaptor type
> > + *
> > + * Returns:
> > + * String representation of the DP dual mode adaptor type
> > + */
> > +const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type)
> > +{
> > +	switch (type) {
> > +	case DRM_DP_DUAL_MODE_NONE:
> > +		return "none";
> > +	case DRM_DP_DUAL_MODE_TYPE1_DVI:
> > +		return "type 1 DVI";
> > +	case DRM_DP_DUAL_MODE_TYPE1_HDMI:
> > +		return "type 1 HDMI";
> > +	case DRM_DP_DUAL_MODE_TYPE2_DVI:
> > +		return "type 2 DVI";
> > +	case DRM_DP_DUAL_MODE_TYPE2_HDMI:
> > +		return "type 2 HDMI";
> > +	default:
> > +		WARN_ON(type != DRM_DP_DUAL_MODE_UNKNOWN);
> > +		return "unknown";
> > +	}
> > +}
> > +EXPORT_SYMBOL(drm_dp_get_dual_mode_type_name);
> > diff --git a/include/drm/drm_dp_dual_mode_helper.h b/include/drm/drm_dp_dual_mode_helper.h
> > new file mode 100644
> > index 000000000000..b4603b9fc03d
> > --- /dev/null
> > +++ b/include/drm/drm_dp_dual_mode_helper.h
> > @@ -0,0 +1,83 @@
> > +/*
> > + * Copyright © 2016 Intel Corporation
> > + *
> > + * Permission is hereby granted, free of charge, to any person obtaining a
> > + * copy of this software and associated documentation files (the "Software"),
> > + * to deal in the Software without restriction, including without limitation
> > + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> > + * and/or sell copies of the Software, and to permit persons to whom the
> > + * Software is furnished to do so, subject to the following conditions:
> > + *
> > + * The above copyright notice and this permission notice shall be included in
> > + * all copies or substantial portions of the Software.
> > + *
> > + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> > + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> > + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> > + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> > + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> > + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> > + * OTHER DEALINGS IN THE SOFTWARE.
> > + */
> > +
> > +#ifndef DRM_DP_DUAL_MODE_HELPER_H
> > +#define DRM_DP_DUAL_MODE_HELPER_H
> > +
> > +#include <linux/types.h>
> > +
> > +/*
> > + * Optional for type 1 DVI adaptors
> > + * Mandatory for type 1 HDMI and type 2 adators
> > + */
> > +#define DP_DUAL_MODE_HDMI_ID 0x00 /* 00-0f */
> > +#define  DP_DUAL_MODE_HDMI_ID_LEN 16
> > +/*
> > + * Optional for type 1 adaptors
> > + * Mandatory for type 2 adators
> > + */
> > +#define DP_DUAL_MODE_ADAPTOR_ID 0x10
> > +#define  DP_DUAL_MODE_REV_MASK 0x07
> > +#define  DP_DUAL_MODE_REV_TYPE2 0x00
> > +#define  DP_DUAL_MODE_TYPE_MASK 0xf0
> > +#define  DP_DUAL_MODE_TYPE_TYPE2 0xa0
> > +#define DP_DUAL_MODE_IEEE_OUI 0x11 /* 11-13*/
> > +#define  DP_DUAL_IEEE_OUI_LEN 3
> > +#define DP_DUAL_DEVICE_ID 0x14 /* 14-19 */
> > +#define  DP_DUAL_DEVICE_ID_LEN 6
> > +#define DP_DUAL_MODE_HARDWARE_REV 0x1a
> > +#define DP_DUAL_MODE_FIRMWARE_MAJOR_REV 0x1b
> > +#define DP_DUAL_MODE_FIRMWARE_MINOR_REV 0x1c
> > +#define DP_DUAL_MODE_MAX_TMDS_CLOCK 0x1d
> > +#define DP_DUAL_MODE_I2C_SPEED_CAP 0x1e
> > +#define DP_DUAL_MODE_TMDS_OEN 0x20
> > +#define  DP_DUAL_MODE_TMDS_DISABLE 0x01
> > +#define DP_DUAL_MODE_HDMI_PIN_CTRL 0x21
> > +#define  DP_DUAL_MODE_CEC_ENABLE 0x01
> > +#define DP_DUAL_MODE_I2C_SPEED_CTRL 0x22
> > +
> > +struct i2c_adapter;
> > +
> > +ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
> > +			      u8 offset, void *buffer, size_t size);
> > +ssize_t drm_dp_dual_mode_write(struct i2c_adapter *adapter,
> > +			       u8 offset, const void *buffer, size_t size);
> > +
> > +enum drm_dp_dual_mode_type {
> > +	DRM_DP_DUAL_MODE_NONE,
> > +	DRM_DP_DUAL_MODE_UNKNOWN,
> > +	DRM_DP_DUAL_MODE_TYPE1_DVI,
> > +	DRM_DP_DUAL_MODE_TYPE1_HDMI,
> > +	DRM_DP_DUAL_MODE_TYPE2_DVI,
> > +	DRM_DP_DUAL_MODE_TYPE2_HDMI,
> > +};
> > +
> > +enum drm_dp_dual_mode_type drm_dp_dual_mode_detect(struct i2c_adapter *adapter);
> > +int drm_dp_dual_mode_max_tmds_clock(enum drm_dp_dual_mode_type type,
> > +				    struct i2c_adapter *adapter);
> > +int drm_dp_dual_mode_get_tmds_output(enum drm_dp_dual_mode_type type,
> > +				     struct i2c_adapter *adapter, bool *enabled);
> > +int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type,
> > +				     struct i2c_adapter *adapter, bool enable);
> > +const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type);
> > +
> > +#endif
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center

Sharma, Shashank May 3, 2016, 4:33 p.m. UTC | #3

On 5/3/2016 12:38 AM, [e-mail] wrote:
> From: Ville Syrjälä <[e-mail]>
>
> Add a helper which aids in the identification of DP dual mode
> (aka. DP++) adaptors. There are several types of adaptors
> specified: type 1 DVI, type 1 HDMI, type 2 DVI, type 2 HDMI
>
> Type 1 adaptors have a max TMDS clock limit of 165MHz, type 2 adaptors
> may go as high as 300MHz and they provide a register informing the
> source device what the actual limit is. Supposedly also type 1 adaptors
> may optionally implement this register. This TMDS clock limit is the
> main reason why we need to identify these adaptors.
>
> Type 1 adaptors provide access to their internal registers and the sink
> DDC bus through I2C. Type 2 adaptors provide this access both via I2C
> and I2C-over-AUX. A type 2 source device may choose to implement either
> of these methods. If a source device implements the I2C-over-AUX
> method, then the driver will obviously need specific support for such
> adaptors since the port is driven like an HDMI port, but DDC
> communication happes over the AUX channel.
>
> This helper should be enough to identify the adaptor type (some
> type 1 DVI adaptors may be a slight exception) and the maximum TMDS
> clock limit. Another feature that may be available is control over
> the TMDS output buffers on the adaptor, possibly allowing for some
> power saving when the TMDS link is down.
>
> Other user controllable features that may be available in the adaptors
> are downstream i2c bus speed control when using i2c-over-aux, and
> some control over the CEC pin. I chose not to provide any helper
> functions for those since I have no use for them in i915 at this time.
> The rest of the registers in the adaptor are mostly just information,
> eg. IEEE OUI, hardware and firmware revision, etc.
>
> v2: Pass adaptor type to helper functions to ease driver implementation
>      Fix a bunch of typoes (Paulo)
>      Add DRM_DP_DUAL_MODE_UNKNOWN for the case where we don't (yet) know
>      the type (Paulo)
>      Reject 0x00 and 0xff DP_DUAL_MODE_MAX_TMDS_CLOCK values (Paulo)
>      Adjust drm_dp_dual_mode_detect() type2 vs. type1 detection to
>      ease future LSPCON enabling
>      Remove the unused DP_DUAL_MODE_LAST_RESERVED define
>
> Cc: [e-mail]
> Cc: Tore Anderson <[e-mail]>
> Cc: Paulo Zanoni <[e-mail]>
> Cc: Shashank Sharma <[e-mail]>
> Cc: Daniel Vetter <[e-mail]>
> Signed-off-by: Ville Syrjälä <[e-mail]>
> ---
>   drivers/gpu/drm/Makefile                  |   2 +-
>   drivers/gpu/drm/drm_dp_dual_mode_helper.c | 356 ++++++++++++++++++++++++++++++
>   include/drm/drm_dp_dual_mode_helper.h     |  83 +++++++
>   3 files changed, 440 insertions(+), 1 deletion(-)
>   create mode 100644 drivers/gpu/drm/drm_dp_dual_mode_helper.c
>   create mode 100644 include/drm/drm_dp_dual_mode_helper.h
>
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index 1a26b4eb1ce0..29f2ee9b9534 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -23,7 +23,7 @@ drm-$(CONFIG_AGP) += drm_agpsupport.o
>
>   drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
>   		drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o \
> -		drm_kms_helper_common.o
> +		drm_kms_helper_common.o drm_dp_dual_mode_helper.o
>
>   drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
>   drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
> diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> new file mode 100644
> index 000000000000..949c0fbeb542
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> @@ -0,0 +1,356 @@
> +/*
> + * Copyright © 2016 Intel Corporation
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the "Software"),
> + * to deal in the Software without restriction, including without limitation
> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> + * OTHER DEALINGS IN THE SOFTWARE.
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/export.h>
> +#include <linux/i2c.h>
> +#include <linux/slab.h>
> +#include <linux/string.h>
> +#include <drm/drm_dp_dual_mode_helper.h>
> +#include <drm/drmP.h>
> +
> +/**
> + * DOC: DP dual mode (aka. DP++) adaptor helpers
> + *
> + * Helper functions to deal with DP dual mode adaptors.
> + *
> + * Type 1:
> + * Adaptor registers (if any) and the sink DDC bus may be accessed via I2C.
> + *
> + * Type 2:
> + * Adaptor registers and sink DDC bus can be accessed either via I2C or
> + * I2C-over-AUX. Source devices may choose to implement either of these
> + * access methods.
> + */
> +
> +#define DP_DUAL_MODE_SLAVE_ADDRESS 0x40
> +
> +/**
> + * drm_dp_dual_mode_read - Read from the DP dual mode adaptor register(s)
> + * adapter: I2C adapter for the DDC bus
> + * offset: register offset
> + * buffer: buffer for return data
> + * size: sizo of the buffer
> + *
> + * Reads @size bytes from the DP dual mode adaptor registers
> + * starting at @offset.
> + *
> + * Returns:
> + * 0 on success, negative error code on failure
> + */
> +ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
> +			      u8 offset, void *buffer, size_t size)
> +{
> +	struct i2c_msg msgs[] = {
> +		{
> +			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> +			.flags = 0,
> +			.len = 1,
> +			.buf = &offset,
> +		},
> +		{
> +			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> +			.flags = I2C_M_RD,
> +			.len = size,
> +			.buf = buffer,
> +		},
> +	};
> +	int ret;
> +
> +	ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
> +	if (ret < 0)
> +		return ret;
> +	if (ret != ARRAY_SIZE(msgs))
> +		return -EPROTO;
> +
> +	return 0;
> +}
> +
> +/**
> + * drm_dp_dual_mode_write - Write to the DP dual mode adaptor register(s)
> + * adapter: I2C adapter for the DDC bus
> + * offset: register offset
> + * buffer: buffer for write data
> + * size: sizo of the buffer
> + *
> + * Writes @size bytes to the DP dual mode adaptor registers
> + * starting at @offset.
> + *
> + * Returns:
> + * 0 on success, negative error code on failure
> + */
> +ssize_t drm_dp_dual_mode_write(struct i2c_adapter *adapter,
> +			       u8 offset, const void *buffer, size_t size)
> +{
> +	struct i2c_msg msg = {
> +		.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> +		.flags = 0,
> +		.len = 1 + size,
> +		.buf = NULL,
> +	};
> +	void *data;
> +	int ret;
> +
> +	data = kmalloc(msg.len, GFP_TEMPORARY);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	msg.buf = data;
> +
> +	memcpy(data, &offset, 1);
> +	memcpy(data + 1, buffer, size);
> +
> +	ret = i2c_transfer(adapter, &msg, 1);
> +
> +	kfree(data);
> +
> +	if (ret < 0)
> +		return ret;
> +	if (ret != 1)
> +		return -EPROTO;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_dual_mode_write);
> +
> +static bool is_hdmi_adaptor(const char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN])
> +{
> +	static const char dp_dual_mode_hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] =
> +		"DP-HDMI ADAPTOR\x04";
> +
> +	return memcmp(hdmi_id, dp_dual_mode_hdmi_id,
> +		      sizeof(dp_dual_mode_hdmi_id)) == 0;
> +}
> +
> +static bool is_type2_adaptor(uint8_t adaptor_id)
> +{
> +	return adaptor_id == (DP_DUAL_MODE_TYPE_TYPE2 |
> +			      DP_DUAL_MODE_REV_TYPE2);
> +}
> +
> +/**
> + * drm_dp_dual_mode_detect - Identify the DP dual mode adaptor
> + * adapter: I2C adapter for the DDC bus
> + *
> + * Attempt to identify the type of the DP dual mode adaptor used.
> + *
> + * Note that when the answer is @DRM_DP_DUAL_MODE_NONE it's not
> + * certain whether we're dealing with a native HDMI port or
> + * a type 1 DVI dual mode adaptor. The driver will have to use
> + * some other hardware/driver specific mechanism to make that
> + * distinction.
> + *
> + * Returns:
> + * The type of the DP dual mode adaptor used
> + */
> +enum drm_dp_dual_mode_type drm_dp_dual_mode_detect(struct i2c_adapter *adapter)
> +{
> +	char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] = {};
> +	uint8_t adaptor_id = 0x00;
> +	ssize_t ret;
> +
> +	/*
> +	 * Let's see if the adaptor is there the by reading the
> +	 * HDMI ID registers.
> +	 *
> +	 * Note that type 1 DVI adaptors are not required to implemnt
> +	 * any registers, and that presents a problem for detection.
> +	 * If the i2c transfer is nacked, we may or may not be dealing
> +	 * with a type 1 DVI adaptor. Some other mechanism of detecting
> +	 * the presence of the adaptor is required. One way would be
> +	 * to check the state of the CONFIG1 pin, Another method would
> +	 * simply require the driver to know whether the port is a DP++
> +	 * port or a native HDMI port. Both of these methods are entirely
> +	 * hardware/driver specific so we can't deal with them here.
> +	 */
> +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_HDMI_ID,
> +				    hdmi_id, sizeof(hdmi_id));
> +	if (ret)
> +		return DRM_DP_DUAL_MODE_UNKNOWN;
> +
> +	/*
> +	 * Sigh. Some (maybe all?) type 1 adaptors are broken and ack
> +	 * the offset but ignore it, and instead they just always return
> +	 * data from the start of the HDMI ID buffer. So for a broken
> +	 * type 1 HDMI adaptor a single byte read will always give us
> +	 * 0x44, and for a type 1 DVI adaptor it should give 0x00
> +	 * (assuming it implements any registers). Fortunately neither
> +	 * of those values will match the type 2 signature of the
> +	 * DP_DUAL_MODE_ADAPTOR_ID register so we can proceed with
> +	 * the type 2 adaptor detection safely even in the presence
> +	 * of broken type 1 adaptors.
> +	 */
> +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_ADAPTOR_ID,
> +				    &adaptor_id, sizeof(adaptor_id));
can we read all 16 bytes in a single read, and then split the characters 
into dongle_signature and adaptor_id ?
> +	if (ret == 0) {
> +		if (is_type2_adaptor(adaptor_id) && is_hdmi_adaptor(hdmi_id))
> +			return DRM_DP_DUAL_MODE_TYPE2_HDMI;
> +		else if (is_type2_adaptor(adaptor_id))
> +			return DRM_DP_DUAL_MODE_TYPE2_DVI;
	can we save one if, or its too late for me to work :) ?
		is_type2_adaptor() {
			is_hdmi_adaptor()
				return type2_hdmi;
			else
				return type2_dvi
		}
> +	}
> +
> +	if (is_hdmi_adaptor(hdmi_id))
> +		return DRM_DP_DUAL_MODE_TYPE1_HDMI;
> +	else
> +		return DRM_DP_DUAL_MODE_TYPE1_DVI;
> +}
> +EXPORT_SYMBOL(drm_dp_dual_mode_detect);
> +
> +/**
> + * drm_dp_dual_mode_max_tmds_clock - Max TMDS clock for DP dual mode adaptor
> + * type: DP dual mode adaptor type
> + * adapter: I2C adapter for the DDC bus
> + *
> + * Determine the max TMDS clock the adaptor supports based on the
> + * type of the dual mode adaptor and the DP_DUAL_MODE_MAX_TMDS_CLOCK
> + * register (on type2 adaptors). As some type 1 adaptors have
> + * problems with registers (see comments in drm_dp_dual_mode_detect())
> + * we don't read the register on those, instead we simply assume
> + * a 165 MHz limit based on the specification.
> + *
> + * Returns:
> + * Maximum supported TMDS clock rate for the DP dual mode adaptor in kHz.
> + */
> +int drm_dp_dual_mode_max_tmds_clock(enum drm_dp_dual_mode_type type,
> +				    struct i2c_adapter *adapter)
> +{
> +	uint8_t max_tmds_clock;
> +	ssize_t ret;
> +
> +	/* native HDMI so no limit */
> +	if (type == DRM_DP_DUAL_MODE_NONE)
> +		return 0;
> +
> +	/*
> +	 * Type 1 adaptors are limited to 165MHz
> +	 * Type 2 adaptors can tells us their limit
> +	 */
> +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
> +		return 165000;
> +
> +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_MAX_TMDS_CLOCK,
> +				    &max_tmds_clock, sizeof(max_tmds_clock));
> +	if (ret || max_tmds_clock == 0x00 || max_tmds_clock == 0xff)
> +		return 165000;
> +
> +	return max_tmds_clock * 5000 / 2;
> +}
> +EXPORT_SYMBOL(drm_dp_dual_mode_max_tmds_clock);
> +
> +/**
> + * drm_dp_dual_mode_get_tmds_output - Get the state of the TMDS output buffers in the DP dual mode adaptor
> + * type: DP dual mode adaptor type
> + * adapter: I2C adapter for the DDC bus
> + * enabled: current state of the TMDS output buffers
> + *
> + * Get the state of the TMDS output buffers in the adaptor. For
> + * type2 adaptors this is queried from the DP_DUAL_MODE_TMDS_OEN
> + * register. As some type 1 adaptors have problems with registers
> + * (see comments in drm_dp_dual_mode_detect()) we don't read the
> + * register on those, instead we simply assume that the buffers
> + * are always enabled.
> + *
> + * Returns:
> + * 0 on success, negative error code on failure
> + */
> +int drm_dp_dual_mode_get_tmds_output(enum drm_dp_dual_mode_type type,
> +				     struct i2c_adapter *adapter,
> +				     bool *enabled)
> +{
> +	uint8_t tmds_oen;
> +	ssize_t ret;
> +
> +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI) {
> +		*enabled = true;
> +		return 0;
> +	}
> +
> +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_TMDS_OEN,
> +				    &tmds_oen, sizeof(tmds_oen));
> +	if (ret)
debug message here might help in failure cases.
> +		return ret;
> +
> +	*enabled = !(tmds_oen & DP_DUAL_MODE_TMDS_DISABLE);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_dual_mode_get_tmds_output);
> +
> +/**
> + * drm_dp_dual_mode_set_tmds_output - Enable/disable TMDS output buffers in the DP dual mode adaptor
> + * type: DP dual mode adaptor type
> + * adapter: I2C adapter for the DDC bus
> + * enable: enable (as opposed to disable) the TMDS output buffers
> + *
> + * Set the state of the TMDS output buffers in the adaptor. For
> + * type2 this is set via the DP_DUAL_MODE_TMDS_OEN register. As
> + * some type 1 adaptors have problems with registers (see comments
> + * in drm_dp_dual_mode_detect()) we avoid touching the register,
> + * making this function a no-op on type 1 adaptors.
> + *
> + * Returns:
> + * 0 on success, negative error code on failure
> + */
> +int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type,
> +				     struct i2c_adapter *adapter, bool enable)
> +{
> +	uint8_t tmds_oen = enable ? 0 : DP_DUAL_MODE_TMDS_DISABLE;
> +	ssize_t ret;
> +
> +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
> +		return 0;
> +
> +	ret = drm_dp_dual_mode_write(adapter, DP_DUAL_MODE_TMDS_OEN,
> +				     &tmds_oen, sizeof(tmds_oen));
> +	if (ret)
debug message here might help in failure cases.
> +		return ret;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_dual_mode_set_tmds_output);
> +
> +/**
> + * drm_dp_get_dual_mode_type_name - Get the name of the DP dual mode adaptor type as a string
> + * type: DP dual mode adaptor type
> + *
> + * Returns:
> + * String representation of the DP dual mode adaptor type
> + */
> +const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type)
> +{
> +	switch (type) {
> +	case DRM_DP_DUAL_MODE_NONE:
> +		return "none";
> +	case DRM_DP_DUAL_MODE_TYPE1_DVI:
> +		return "type 1 DVI";
> +	case DRM_DP_DUAL_MODE_TYPE1_HDMI:
> +		return "type 1 HDMI";
> +	case DRM_DP_DUAL_MODE_TYPE2_DVI:
> +		return "type 2 DVI";
> +	case DRM_DP_DUAL_MODE_TYPE2_HDMI:
> +		return "type 2 HDMI";
> +	default:
> +		WARN_ON(type != DRM_DP_DUAL_MODE_UNKNOWN);
do we need a warning here, or a DRM_ERROR should work ?
I am afraid we will show a back-trace for all non-compliant adapters.
> +		return "unknown";
> +	}
> +}
> +EXPORT_SYMBOL(drm_dp_get_dual_mode_type_name);
> diff --git a/include/drm/drm_dp_dual_mode_helper.h b/include/drm/drm_dp_dual_mode_helper.h
> new file mode 100644
> index 000000000000..b4603b9fc03d
> --- /dev/null
> +++ b/include/drm/drm_dp_dual_mode_helper.h
> @@ -0,0 +1,83 @@
> +/*
> + * Copyright © 2016 Intel Corporation
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the "Software"),
> + * to deal in the Software without restriction, including without limitation
> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> + * OTHER DEALINGS IN THE SOFTWARE.
> + */
> +
> +#ifndef DRM_DP_DUAL_MODE_HELPER_H
> +#define DRM_DP_DUAL_MODE_HELPER_H
> +
> +#include <linux/types.h>
> +
> +/*
> + * Optional for type 1 DVI adaptors
> + * Mandatory for type 1 HDMI and type 2 adators
> + */
> +#define DP_DUAL_MODE_HDMI_ID 0x00 /* 00-0f */
> +#define  DP_DUAL_MODE_HDMI_ID_LEN 16
> +/*
> + * Optional for type 1 adaptors
> + * Mandatory for type 2 adators
> + */
> +#define DP_DUAL_MODE_ADAPTOR_ID 0x10
> +#define  DP_DUAL_MODE_REV_MASK 0x07
> +#define  DP_DUAL_MODE_REV_TYPE2 0x00
> +#define  DP_DUAL_MODE_TYPE_MASK 0xf0
> +#define  DP_DUAL_MODE_TYPE_TYPE2 0xa0
> +#define DP_DUAL_MODE_IEEE_OUI 0x11 /* 11-13*/
> +#define  DP_DUAL_IEEE_OUI_LEN 3
> +#define DP_DUAL_DEVICE_ID 0x14 /* 14-19 */
> +#define  DP_DUAL_DEVICE_ID_LEN 6
> +#define DP_DUAL_MODE_HARDWARE_REV 0x1a
> +#define DP_DUAL_MODE_FIRMWARE_MAJOR_REV 0x1b
> +#define DP_DUAL_MODE_FIRMWARE_MINOR_REV 0x1c
> +#define DP_DUAL_MODE_MAX_TMDS_CLOCK 0x1d
> +#define DP_DUAL_MODE_I2C_SPEED_CAP 0x1e
> +#define DP_DUAL_MODE_TMDS_OEN 0x20
> +#define  DP_DUAL_MODE_TMDS_DISABLE 0x01
> +#define DP_DUAL_MODE_HDMI_PIN_CTRL 0x21
> +#define  DP_DUAL_MODE_CEC_ENABLE 0x01
> +#define DP_DUAL_MODE_I2C_SPEED_CTRL 0x22
> +
> +struct i2c_adapter;
> +
> +ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
> +			      u8 offset, void *buffer, size_t size);
> +ssize_t drm_dp_dual_mode_write(struct i2c_adapter *adapter,
> +			       u8 offset, const void *buffer, size_t size);
> +
> +enum drm_dp_dual_mode_type {
> +	DRM_DP_DUAL_MODE_NONE,
what does dual mode none indicate (considering we have an unknown case 
below) ?
Regards
Shashank
> +	DRM_DP_DUAL_MODE_UNKNOWN,
> +	DRM_DP_DUAL_MODE_TYPE1_DVI,
> +	DRM_DP_DUAL_MODE_TYPE1_HDMI,
> +	DRM_DP_DUAL_MODE_TYPE2_DVI,
> +	DRM_DP_DUAL_MODE_TYPE2_HDMI,
> +};
> +
> +enum drm_dp_dual_mode_type drm_dp_dual_mode_detect(struct i2c_adapter *adapter);
> +int drm_dp_dual_mode_max_tmds_clock(enum drm_dp_dual_mode_type type,
> +				    struct i2c_adapter *adapter);
> +int drm_dp_dual_mode_get_tmds_output(enum drm_dp_dual_mode_type type,
> +				     struct i2c_adapter *adapter, bool *enabled);
> +int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type,
> +				     struct i2c_adapter *adapter, bool enable);
> +const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type);
> +
> +#endif
>

Ville Syrjälä May 3, 2016, 5:38 p.m. UTC | #4

On Tue, May 03, 2016 at 10:03:30PM +0530, Sharma, Shashank wrote:
> 
> 
> On 5/3/2016 12:38 AM, [e-mail] wrote:
> > From: Ville Syrjälä <[e-mail]>
> >
> > Add a helper which aids in the identification of DP dual mode
> > (aka. DP++) adaptors. There are several types of adaptors
> > specified: type 1 DVI, type 1 HDMI, type 2 DVI, type 2 HDMI
> >
> > Type 1 adaptors have a max TMDS clock limit of 165MHz, type 2 adaptors
> > may go as high as 300MHz and they provide a register informing the
> > source device what the actual limit is. Supposedly also type 1 adaptors
> > may optionally implement this register. This TMDS clock limit is the
> > main reason why we need to identify these adaptors.
> >
> > Type 1 adaptors provide access to their internal registers and the sink
> > DDC bus through I2C. Type 2 adaptors provide this access both via I2C
> > and I2C-over-AUX. A type 2 source device may choose to implement either
> > of these methods. If a source device implements the I2C-over-AUX
> > method, then the driver will obviously need specific support for such
> > adaptors since the port is driven like an HDMI port, but DDC
> > communication happes over the AUX channel.
> >
> > This helper should be enough to identify the adaptor type (some
> > type 1 DVI adaptors may be a slight exception) and the maximum TMDS
> > clock limit. Another feature that may be available is control over
> > the TMDS output buffers on the adaptor, possibly allowing for some
> > power saving when the TMDS link is down.
> >
> > Other user controllable features that may be available in the adaptors
> > are downstream i2c bus speed control when using i2c-over-aux, and
> > some control over the CEC pin. I chose not to provide any helper
> > functions for those since I have no use for them in i915 at this time.
> > The rest of the registers in the adaptor are mostly just information,
> > eg. IEEE OUI, hardware and firmware revision, etc.
> >
> > v2: Pass adaptor type to helper functions to ease driver implementation
> >      Fix a bunch of typoes (Paulo)
> >      Add DRM_DP_DUAL_MODE_UNKNOWN for the case where we don't (yet) know
> >      the type (Paulo)
> >      Reject 0x00 and 0xff DP_DUAL_MODE_MAX_TMDS_CLOCK values (Paulo)
> >      Adjust drm_dp_dual_mode_detect() type2 vs. type1 detection to
> >      ease future LSPCON enabling
> >      Remove the unused DP_DUAL_MODE_LAST_RESERVED define
> >
> > Cc: [e-mail]
> > Cc: Tore Anderson <[e-mail]>
> > Cc: Paulo Zanoni <[e-mail]>
> > Cc: Shashank Sharma <[e-mail]>
> > Cc: Daniel Vetter <[e-mail]>
> > Signed-off-by: Ville Syrjälä <[e-mail]>
> > ---
> >   drivers/gpu/drm/Makefile                  |   2 +-
> >   drivers/gpu/drm/drm_dp_dual_mode_helper.c | 356 ++++++++++++++++++++++++++++++
> >   include/drm/drm_dp_dual_mode_helper.h     |  83 +++++++
> >   3 files changed, 440 insertions(+), 1 deletion(-)
> >   create mode 100644 drivers/gpu/drm/drm_dp_dual_mode_helper.c
> >   create mode 100644 include/drm/drm_dp_dual_mode_helper.h
> >
> > diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> > index 1a26b4eb1ce0..29f2ee9b9534 100644
> > --- a/drivers/gpu/drm/Makefile
> > +++ b/drivers/gpu/drm/Makefile
> > @@ -23,7 +23,7 @@ drm-$(CONFIG_AGP) += drm_agpsupport.o
> >
> >   drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
> >   		drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o \
> > -		drm_kms_helper_common.o
> > +		drm_kms_helper_common.o drm_dp_dual_mode_helper.o
> >
> >   drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
> >   drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
> > diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> > new file mode 100644
> > index 000000000000..949c0fbeb542
> > --- /dev/null
> > +++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
> > @@ -0,0 +1,356 @@
> > +/*
> > + * Copyright © 2016 Intel Corporation
> > + *
> > + * Permission is hereby granted, free of charge, to any person obtaining a
> > + * copy of this software and associated documentation files (the "Software"),
> > + * to deal in the Software without restriction, including without limitation
> > + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> > + * and/or sell copies of the Software, and to permit persons to whom the
> > + * Software is furnished to do so, subject to the following conditions:
> > + *
> > + * The above copyright notice and this permission notice shall be included in
> > + * all copies or substantial portions of the Software.
> > + *
> > + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> > + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> > + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> > + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> > + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> > + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> > + * OTHER DEALINGS IN THE SOFTWARE.
> > + */
> > +
> > +#include <linux/errno.h>
> > +#include <linux/export.h>
> > +#include <linux/i2c.h>
> > +#include <linux/slab.h>
> > +#include <linux/string.h>
> > +#include <drm/drm_dp_dual_mode_helper.h>
> > +#include <drm/drmP.h>
> > +
> > +/**
> > + * DOC: DP dual mode (aka. DP++) adaptor helpers
> > + *
> > + * Helper functions to deal with DP dual mode adaptors.
> > + *
> > + * Type 1:
> > + * Adaptor registers (if any) and the sink DDC bus may be accessed via I2C.
> > + *
> > + * Type 2:
> > + * Adaptor registers and sink DDC bus can be accessed either via I2C or
> > + * I2C-over-AUX. Source devices may choose to implement either of these
> > + * access methods.
> > + */
> > +
> > +#define DP_DUAL_MODE_SLAVE_ADDRESS 0x40
> > +
> > +/**
> > + * drm_dp_dual_mode_read - Read from the DP dual mode adaptor register(s)
> > + * adapter: I2C adapter for the DDC bus
> > + * offset: register offset
> > + * buffer: buffer for return data
> > + * size: sizo of the buffer
> > + *
> > + * Reads @size bytes from the DP dual mode adaptor registers
> > + * starting at @offset.
> > + *
> > + * Returns:
> > + * 0 on success, negative error code on failure
> > + */
> > +ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
> > +			      u8 offset, void *buffer, size_t size)
> > +{
> > +	struct i2c_msg msgs[] = {
> > +		{
> > +			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> > +			.flags = 0,
> > +			.len = 1,
> > +			.buf = &offset,
> > +		},
> > +		{
> > +			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> > +			.flags = I2C_M_RD,
> > +			.len = size,
> > +			.buf = buffer,
> > +		},
> > +	};
> > +	int ret;
> > +
> > +	ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
> > +	if (ret < 0)
> > +		return ret;
> > +	if (ret != ARRAY_SIZE(msgs))
> > +		return -EPROTO;
> > +
> > +	return 0;
> > +}
> > +
> > +/**
> > + * drm_dp_dual_mode_write - Write to the DP dual mode adaptor register(s)
> > + * adapter: I2C adapter for the DDC bus
> > + * offset: register offset
> > + * buffer: buffer for write data
> > + * size: sizo of the buffer
> > + *
> > + * Writes @size bytes to the DP dual mode adaptor registers
> > + * starting at @offset.
> > + *
> > + * Returns:
> > + * 0 on success, negative error code on failure
> > + */
> > +ssize_t drm_dp_dual_mode_write(struct i2c_adapter *adapter,
> > +			       u8 offset, const void *buffer, size_t size)
> > +{
> > +	struct i2c_msg msg = {
> > +		.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
> > +		.flags = 0,
> > +		.len = 1 + size,
> > +		.buf = NULL,
> > +	};
> > +	void *data;
> > +	int ret;
> > +
> > +	data = kmalloc(msg.len, GFP_TEMPORARY);
> > +	if (!data)
> > +		return -ENOMEM;
> > +
> > +	msg.buf = data;
> > +
> > +	memcpy(data, &offset, 1);
> > +	memcpy(data + 1, buffer, size);
> > +
> > +	ret = i2c_transfer(adapter, &msg, 1);
> > +
> > +	kfree(data);
> > +
> > +	if (ret < 0)
> > +		return ret;
> > +	if (ret != 1)
> > +		return -EPROTO;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_dp_dual_mode_write);
> > +
> > +static bool is_hdmi_adaptor(const char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN])
> > +{
> > +	static const char dp_dual_mode_hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] =
> > +		"DP-HDMI ADAPTOR\x04";
> > +
> > +	return memcmp(hdmi_id, dp_dual_mode_hdmi_id,
> > +		      sizeof(dp_dual_mode_hdmi_id)) == 0;
> > +}
> > +
> > +static bool is_type2_adaptor(uint8_t adaptor_id)
> > +{
> > +	return adaptor_id == (DP_DUAL_MODE_TYPE_TYPE2 |
> > +			      DP_DUAL_MODE_REV_TYPE2);
> > +}
> > +
> > +/**
> > + * drm_dp_dual_mode_detect - Identify the DP dual mode adaptor
> > + * adapter: I2C adapter for the DDC bus
> > + *
> > + * Attempt to identify the type of the DP dual mode adaptor used.
> > + *
> > + * Note that when the answer is @DRM_DP_DUAL_MODE_NONE it's not
> > + * certain whether we're dealing with a native HDMI port or
> > + * a type 1 DVI dual mode adaptor. The driver will have to use
> > + * some other hardware/driver specific mechanism to make that
> > + * distinction.
> > + *
> > + * Returns:
> > + * The type of the DP dual mode adaptor used
> > + */
> > +enum drm_dp_dual_mode_type drm_dp_dual_mode_detect(struct i2c_adapter *adapter)
> > +{
> > +	char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] = {};
> > +	uint8_t adaptor_id = 0x00;
> > +	ssize_t ret;
> > +
> > +	/*
> > +	 * Let's see if the adaptor is there the by reading the
> > +	 * HDMI ID registers.
> > +	 *
> > +	 * Note that type 1 DVI adaptors are not required to implemnt
> > +	 * any registers, and that presents a problem for detection.
> > +	 * If the i2c transfer is nacked, we may or may not be dealing
> > +	 * with a type 1 DVI adaptor. Some other mechanism of detecting
> > +	 * the presence of the adaptor is required. One way would be
> > +	 * to check the state of the CONFIG1 pin, Another method would
> > +	 * simply require the driver to know whether the port is a DP++
> > +	 * port or a native HDMI port. Both of these methods are entirely
> > +	 * hardware/driver specific so we can't deal with them here.
> > +	 */
> > +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_HDMI_ID,
> > +				    hdmi_id, sizeof(hdmi_id));
> > +	if (ret)
> > +		return DRM_DP_DUAL_MODE_UNKNOWN;
> > +
> > +	/*
> > +	 * Sigh. Some (maybe all?) type 1 adaptors are broken and ack
> > +	 * the offset but ignore it, and instead they just always return
> > +	 * data from the start of the HDMI ID buffer. So for a broken
> > +	 * type 1 HDMI adaptor a single byte read will always give us
> > +	 * 0x44, and for a type 1 DVI adaptor it should give 0x00
> > +	 * (assuming it implements any registers). Fortunately neither
> > +	 * of those values will match the type 2 signature of the
> > +	 * DP_DUAL_MODE_ADAPTOR_ID register so we can proceed with
> > +	 * the type 2 adaptor detection safely even in the presence
> > +	 * of broken type 1 adaptors.
> > +	 */
> > +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_ADAPTOR_ID,
> > +				    &adaptor_id, sizeof(adaptor_id));
> can we read all 16 bytes in a single read, and then split the characters 
> into dongle_signature and adaptor_id ?

I think Paulo suggested the same thing more or less. Hmm. Let me think.
I'm not sure we want to do that because IIRC the spec says that type 1
HDMI adaptors aren't required to support any registers beyond the HDMI
ID, so I'm not sure some of them might not return an error if we try to
read more than that, and that could then cause the HDMI ID read fail as
well even if it's indeed present. I don't think any of the adaptors I
tested behaved that way, but I don't have that many of them here.

It's a bit of a shame the i2c subsystem doesn't report the number of 
bytes succesfully transferred. It just returns the number of messages
succesfully transferred. And if a message is only partially
transferred, I think we'd just get a negative error code back.

> > +	if (ret == 0) {
> > +		if (is_type2_adaptor(adaptor_id) && is_hdmi_adaptor(hdmi_id))
> > +			return DRM_DP_DUAL_MODE_TYPE2_HDMI;
> > +		else if (is_type2_adaptor(adaptor_id))
> > +			return DRM_DP_DUAL_MODE_TYPE2_DVI;
> 	can we save one if, or its too late for me to work :) ?
> 		is_type2_adaptor() {
> 			is_hdmi_adaptor()
> 				return type2_hdmi;
> 			else
> 				return type2_dvi
> 		}

I wanted to avoid nesting too deeply here. But the line ended up quite
long anyway, so I guess the extra indent wouldn't really look any
worse than this.

> > +	}
> > +
> > +	if (is_hdmi_adaptor(hdmi_id))
> > +		return DRM_DP_DUAL_MODE_TYPE1_HDMI;
> > +	else
> > +		return DRM_DP_DUAL_MODE_TYPE1_DVI;
> > +}
> > +EXPORT_SYMBOL(drm_dp_dual_mode_detect);
> > +
> > +/**
> > + * drm_dp_dual_mode_max_tmds_clock - Max TMDS clock for DP dual mode adaptor
> > + * type: DP dual mode adaptor type
> > + * adapter: I2C adapter for the DDC bus
> > + *
> > + * Determine the max TMDS clock the adaptor supports based on the
> > + * type of the dual mode adaptor and the DP_DUAL_MODE_MAX_TMDS_CLOCK
> > + * register (on type2 adaptors). As some type 1 adaptors have
> > + * problems with registers (see comments in drm_dp_dual_mode_detect())
> > + * we don't read the register on those, instead we simply assume
> > + * a 165 MHz limit based on the specification.
> > + *
> > + * Returns:
> > + * Maximum supported TMDS clock rate for the DP dual mode adaptor in kHz.
> > + */
> > +int drm_dp_dual_mode_max_tmds_clock(enum drm_dp_dual_mode_type type,
> > +				    struct i2c_adapter *adapter)
> > +{
> > +	uint8_t max_tmds_clock;
> > +	ssize_t ret;
> > +
> > +	/* native HDMI so no limit */
> > +	if (type == DRM_DP_DUAL_MODE_NONE)
> > +		return 0;
> > +
> > +	/*
> > +	 * Type 1 adaptors are limited to 165MHz
> > +	 * Type 2 adaptors can tells us their limit
> > +	 */
> > +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
> > +		return 165000;
> > +
> > +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_MAX_TMDS_CLOCK,
> > +				    &max_tmds_clock, sizeof(max_tmds_clock));
> > +	if (ret || max_tmds_clock == 0x00 || max_tmds_clock == 0xff)
> > +		return 165000;
> > +
> > +	return max_tmds_clock * 5000 / 2;
> > +}
> > +EXPORT_SYMBOL(drm_dp_dual_mode_max_tmds_clock);
> > +
> > +/**
> > + * drm_dp_dual_mode_get_tmds_output - Get the state of the TMDS output buffers in the DP dual mode adaptor
> > + * type: DP dual mode adaptor type
> > + * adapter: I2C adapter for the DDC bus
> > + * enabled: current state of the TMDS output buffers
> > + *
> > + * Get the state of the TMDS output buffers in the adaptor. For
> > + * type2 adaptors this is queried from the DP_DUAL_MODE_TMDS_OEN
> > + * register. As some type 1 adaptors have problems with registers
> > + * (see comments in drm_dp_dual_mode_detect()) we don't read the
> > + * register on those, instead we simply assume that the buffers
> > + * are always enabled.
> > + *
> > + * Returns:
> > + * 0 on success, negative error code on failure
> > + */
> > +int drm_dp_dual_mode_get_tmds_output(enum drm_dp_dual_mode_type type,
> > +				     struct i2c_adapter *adapter,
> > +				     bool *enabled)
> > +{
> > +	uint8_t tmds_oen;
> > +	ssize_t ret;
> > +
> > +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI) {
> > +		*enabled = true;
> > +		return 0;
> > +	}
> > +
> > +	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_TMDS_OEN,
> > +				    &tmds_oen, sizeof(tmds_oen));
> > +	if (ret)
> debug message here might help in failure cases.

Sure, I can add it.

> > +		return ret;
> > +
> > +	*enabled = !(tmds_oen & DP_DUAL_MODE_TMDS_DISABLE);
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_dp_dual_mode_get_tmds_output);
> > +
> > +/**
> > + * drm_dp_dual_mode_set_tmds_output - Enable/disable TMDS output buffers in the DP dual mode adaptor
> > + * type: DP dual mode adaptor type
> > + * adapter: I2C adapter for the DDC bus
> > + * enable: enable (as opposed to disable) the TMDS output buffers
> > + *
> > + * Set the state of the TMDS output buffers in the adaptor. For
> > + * type2 this is set via the DP_DUAL_MODE_TMDS_OEN register. As
> > + * some type 1 adaptors have problems with registers (see comments
> > + * in drm_dp_dual_mode_detect()) we avoid touching the register,
> > + * making this function a no-op on type 1 adaptors.
> > + *
> > + * Returns:
> > + * 0 on success, negative error code on failure
> > + */
> > +int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type,
> > +				     struct i2c_adapter *adapter, bool enable)
> > +{
> > +	uint8_t tmds_oen = enable ? 0 : DP_DUAL_MODE_TMDS_DISABLE;
> > +	ssize_t ret;
> > +
> > +	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
> > +		return 0;
> > +
> > +	ret = drm_dp_dual_mode_write(adapter, DP_DUAL_MODE_TMDS_OEN,
> > +				     &tmds_oen, sizeof(tmds_oen));
> > +	if (ret)
> debug message here might help in failure cases.

can do.

> > +		return ret;
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_dp_dual_mode_set_tmds_output);
> > +
> > +/**
> > + * drm_dp_get_dual_mode_type_name - Get the name of the DP dual mode adaptor type as a string
> > + * type: DP dual mode adaptor type
> > + *
> > + * Returns:
> > + * String representation of the DP dual mode adaptor type
> > + */
> > +const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type)
> > +{
> > +	switch (type) {
> > +	case DRM_DP_DUAL_MODE_NONE:
> > +		return "none";
> > +	case DRM_DP_DUAL_MODE_TYPE1_DVI:
> > +		return "type 1 DVI";
> > +	case DRM_DP_DUAL_MODE_TYPE1_HDMI:
> > +		return "type 1 HDMI";
> > +	case DRM_DP_DUAL_MODE_TYPE2_DVI:
> > +		return "type 2 DVI";
> > +	case DRM_DP_DUAL_MODE_TYPE2_HDMI:
> > +		return "type 2 HDMI";
> > +	default:
> > +		WARN_ON(type != DRM_DP_DUAL_MODE_UNKNOWN);
> do we need a warning here, or a DRM_ERROR should work ?
> I am afraid we will show a back-trace for all non-compliant adapters.

If someone passes in an invalid type, that's a bug in the caller. So
this should never happen.

> > +		return "unknown";
> > +	}
> > +}
> > +EXPORT_SYMBOL(drm_dp_get_dual_mode_type_name);
> > diff --git a/include/drm/drm_dp_dual_mode_helper.h b/include/drm/drm_dp_dual_mode_helper.h
> > new file mode 100644
> > index 000000000000..b4603b9fc03d
> > --- /dev/null
> > +++ b/include/drm/drm_dp_dual_mode_helper.h
> > @@ -0,0 +1,83 @@
> > +/*
> > + * Copyright © 2016 Intel Corporation
> > + *
> > + * Permission is hereby granted, free of charge, to any person obtaining a
> > + * copy of this software and associated documentation files (the "Software"),
> > + * to deal in the Software without restriction, including without limitation
> > + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> > + * and/or sell copies of the Software, and to permit persons to whom the
> > + * Software is furnished to do so, subject to the following conditions:
> > + *
> > + * The above copyright notice and this permission notice shall be included in
> > + * all copies or substantial portions of the Software.
> > + *
> > + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> > + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> > + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> > + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> > + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> > + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> > + * OTHER DEALINGS IN THE SOFTWARE.
> > + */
> > +
> > +#ifndef DRM_DP_DUAL_MODE_HELPER_H
> > +#define DRM_DP_DUAL_MODE_HELPER_H
> > +
> > +#include <linux/types.h>
> > +
> > +/*
> > + * Optional for type 1 DVI adaptors
> > + * Mandatory for type 1 HDMI and type 2 adators
> > + */
> > +#define DP_DUAL_MODE_HDMI_ID 0x00 /* 00-0f */
> > +#define  DP_DUAL_MODE_HDMI_ID_LEN 16
> > +/*
> > + * Optional for type 1 adaptors
> > + * Mandatory for type 2 adators
> > + */
> > +#define DP_DUAL_MODE_ADAPTOR_ID 0x10
> > +#define  DP_DUAL_MODE_REV_MASK 0x07
> > +#define  DP_DUAL_MODE_REV_TYPE2 0x00
> > +#define  DP_DUAL_MODE_TYPE_MASK 0xf0
> > +#define  DP_DUAL_MODE_TYPE_TYPE2 0xa0
> > +#define DP_DUAL_MODE_IEEE_OUI 0x11 /* 11-13*/
> > +#define  DP_DUAL_IEEE_OUI_LEN 3
> > +#define DP_DUAL_DEVICE_ID 0x14 /* 14-19 */
> > +#define  DP_DUAL_DEVICE_ID_LEN 6
> > +#define DP_DUAL_MODE_HARDWARE_REV 0x1a
> > +#define DP_DUAL_MODE_FIRMWARE_MAJOR_REV 0x1b
> > +#define DP_DUAL_MODE_FIRMWARE_MINOR_REV 0x1c
> > +#define DP_DUAL_MODE_MAX_TMDS_CLOCK 0x1d
> > +#define DP_DUAL_MODE_I2C_SPEED_CAP 0x1e
> > +#define DP_DUAL_MODE_TMDS_OEN 0x20
> > +#define  DP_DUAL_MODE_TMDS_DISABLE 0x01
> > +#define DP_DUAL_MODE_HDMI_PIN_CTRL 0x21
> > +#define  DP_DUAL_MODE_CEC_ENABLE 0x01
> > +#define DP_DUAL_MODE_I2C_SPEED_CTRL 0x22
> > +
> > +struct i2c_adapter;
> > +
> > +ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
> > +			      u8 offset, void *buffer, size_t size);
> > +ssize_t drm_dp_dual_mode_write(struct i2c_adapter *adapter,
> > +			       u8 offset, const void *buffer, size_t size);
> > +
> > +enum drm_dp_dual_mode_type {
> > +	DRM_DP_DUAL_MODE_NONE,
> what does dual mode none indicate (considering we have an unknown case 
> below) ?

It mean we know that there is no dual mode adaptor, meaning we're
dealing with a native HDMI port. Originally I had just the NONE, but
Paulo requested that we make the UNKNOWN case more explicit so I split
it into two. It's always the driver's responsibility to refine the
detection result to NONE or TYPE1_DVI if drm_dp_dual_mode_detect()
returns UNKNOWN.

> Regards
> Shashank
> > +	DRM_DP_DUAL_MODE_UNKNOWN,
> > +	DRM_DP_DUAL_MODE_TYPE1_DVI,
> > +	DRM_DP_DUAL_MODE_TYPE1_HDMI,
> > +	DRM_DP_DUAL_MODE_TYPE2_DVI,
> > +	DRM_DP_DUAL_MODE_TYPE2_HDMI,
> > +};
> > +
> > +enum drm_dp_dual_mode_type drm_dp_dual_mode_detect(struct i2c_adapter *adapter);
> > +int drm_dp_dual_mode_max_tmds_clock(enum drm_dp_dual_mode_type type,
> > +				    struct i2c_adapter *adapter);
> > +int drm_dp_dual_mode_get_tmds_output(enum drm_dp_dual_mode_type type,
> > +				     struct i2c_adapter *adapter, bool *enabled);
> > +int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type,
> > +				     struct i2c_adapter *adapter, bool enable);
> > +const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type);
> > +
> > +#endif
> >

Patch

diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 1a26b4eb1ce0..29f2ee9b9534 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -23,7 +23,7 @@  drm-$(CONFIG_AGP) += drm_agpsupport.o
 
 drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
 		drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o \
-		drm_kms_helper_common.o
+		drm_kms_helper_common.o drm_dp_dual_mode_helper.o
 
 drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
 drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
new file mode 100644
index 000000000000..949c0fbeb542
--- /dev/null
+++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
@@ -0,0 +1,356 @@ 
+/*
+ * Copyright © 2016 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <linux/errno.h>
+#include <linux/export.h>
+#include <linux/i2c.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <drm/drm_dp_dual_mode_helper.h>
+#include <drm/drmP.h>
+
+/**
+ * DOC: DP dual mode (aka. DP++) adaptor helpers
+ *
+ * Helper functions to deal with DP dual mode adaptors.
+ *
+ * Type 1:
+ * Adaptor registers (if any) and the sink DDC bus may be accessed via I2C.
+ *
+ * Type 2:
+ * Adaptor registers and sink DDC bus can be accessed either via I2C or
+ * I2C-over-AUX. Source devices may choose to implement either of these
+ * access methods.
+ */
+
+#define DP_DUAL_MODE_SLAVE_ADDRESS 0x40
+
+/**
+ * drm_dp_dual_mode_read - Read from the DP dual mode adaptor register(s)
+ * adapter: I2C adapter for the DDC bus
+ * offset: register offset
+ * buffer: buffer for return data
+ * size: sizo of the buffer
+ *
+ * Reads @size bytes from the DP dual mode adaptor registers
+ * starting at @offset.
+ *
+ * Returns:
+ * 0 on success, negative error code on failure
+ */
+ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
+			      u8 offset, void *buffer, size_t size)
+{
+	struct i2c_msg msgs[] = {
+		{
+			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
+			.flags = 0,
+			.len = 1,
+			.buf = &offset,
+		},
+		{
+			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
+			.flags = I2C_M_RD,
+			.len = size,
+			.buf = buffer,
+		},
+	};
+	int ret;
+
+	ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
+	if (ret < 0)
+		return ret;
+	if (ret != ARRAY_SIZE(msgs))
+		return -EPROTO;
+
+	return 0;
+}
+
+/**
+ * drm_dp_dual_mode_write - Write to the DP dual mode adaptor register(s)
+ * adapter: I2C adapter for the DDC bus
+ * offset: register offset
+ * buffer: buffer for write data
+ * size: sizo of the buffer
+ *
+ * Writes @size bytes to the DP dual mode adaptor registers
+ * starting at @offset.
+ *
+ * Returns:
+ * 0 on success, negative error code on failure
+ */
+ssize_t drm_dp_dual_mode_write(struct i2c_adapter *adapter,
+			       u8 offset, const void *buffer, size_t size)
+{
+	struct i2c_msg msg = {
+		.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
+		.flags = 0,
+		.len = 1 + size,
+		.buf = NULL,
+	};
+	void *data;
+	int ret;
+
+	data = kmalloc(msg.len, GFP_TEMPORARY);
+	if (!data)
+		return -ENOMEM;
+
+	msg.buf = data;
+
+	memcpy(data, &offset, 1);
+	memcpy(data + 1, buffer, size);
+
+	ret = i2c_transfer(adapter, &msg, 1);
+
+	kfree(data);
+
+	if (ret < 0)
+		return ret;
+	if (ret != 1)
+		return -EPROTO;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_dual_mode_write);
+
+static bool is_hdmi_adaptor(const char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN])
+{
+	static const char dp_dual_mode_hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] =
+		"DP-HDMI ADAPTOR\x04";
+
+	return memcmp(hdmi_id, dp_dual_mode_hdmi_id,
+		      sizeof(dp_dual_mode_hdmi_id)) == 0;
+}
+
+static bool is_type2_adaptor(uint8_t adaptor_id)
+{
+	return adaptor_id == (DP_DUAL_MODE_TYPE_TYPE2 |
+			      DP_DUAL_MODE_REV_TYPE2);
+}
+
+/**
+ * drm_dp_dual_mode_detect - Identify the DP dual mode adaptor
+ * adapter: I2C adapter for the DDC bus
+ *
+ * Attempt to identify the type of the DP dual mode adaptor used.
+ *
+ * Note that when the answer is @DRM_DP_DUAL_MODE_NONE it's not
+ * certain whether we're dealing with a native HDMI port or
+ * a type 1 DVI dual mode adaptor. The driver will have to use
+ * some other hardware/driver specific mechanism to make that
+ * distinction.
+ *
+ * Returns:
+ * The type of the DP dual mode adaptor used
+ */
+enum drm_dp_dual_mode_type drm_dp_dual_mode_detect(struct i2c_adapter *adapter)
+{
+	char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] = {};
+	uint8_t adaptor_id = 0x00;
+	ssize_t ret;
+
+	/*
+	 * Let's see if the adaptor is there the by reading the
+	 * HDMI ID registers.
+	 *
+	 * Note that type 1 DVI adaptors are not required to implemnt
+	 * any registers, and that presents a problem for detection.
+	 * If the i2c transfer is nacked, we may or may not be dealing
+	 * with a type 1 DVI adaptor. Some other mechanism of detecting
+	 * the presence of the adaptor is required. One way would be
+	 * to check the state of the CONFIG1 pin, Another method would
+	 * simply require the driver to know whether the port is a DP++
+	 * port or a native HDMI port. Both of these methods are entirely
+	 * hardware/driver specific so we can't deal with them here.
+	 */
+	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_HDMI_ID,
+				    hdmi_id, sizeof(hdmi_id));
+	if (ret)
+		return DRM_DP_DUAL_MODE_UNKNOWN;
+
+	/*
+	 * Sigh. Some (maybe all?) type 1 adaptors are broken and ack
+	 * the offset but ignore it, and instead they just always return
+	 * data from the start of the HDMI ID buffer. So for a broken
+	 * type 1 HDMI adaptor a single byte read will always give us
+	 * 0x44, and for a type 1 DVI adaptor it should give 0x00
+	 * (assuming it implements any registers). Fortunately neither
+	 * of those values will match the type 2 signature of the
+	 * DP_DUAL_MODE_ADAPTOR_ID register so we can proceed with
+	 * the type 2 adaptor detection safely even in the presence
+	 * of broken type 1 adaptors.
+	 */
+	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_ADAPTOR_ID,
+				    &adaptor_id, sizeof(adaptor_id));
+	if (ret == 0) {
+		if (is_type2_adaptor(adaptor_id) && is_hdmi_adaptor(hdmi_id))
+			return DRM_DP_DUAL_MODE_TYPE2_HDMI;
+		else if (is_type2_adaptor(adaptor_id))
+			return DRM_DP_DUAL_MODE_TYPE2_DVI;
+	}
+
+	if (is_hdmi_adaptor(hdmi_id))
+		return DRM_DP_DUAL_MODE_TYPE1_HDMI;
+	else
+		return DRM_DP_DUAL_MODE_TYPE1_DVI;
+}
+EXPORT_SYMBOL(drm_dp_dual_mode_detect);
+
+/**
+ * drm_dp_dual_mode_max_tmds_clock - Max TMDS clock for DP dual mode adaptor
+ * type: DP dual mode adaptor type
+ * adapter: I2C adapter for the DDC bus
+ *
+ * Determine the max TMDS clock the adaptor supports based on the
+ * type of the dual mode adaptor and the DP_DUAL_MODE_MAX_TMDS_CLOCK
+ * register (on type2 adaptors). As some type 1 adaptors have
+ * problems with registers (see comments in drm_dp_dual_mode_detect())
+ * we don't read the register on those, instead we simply assume
+ * a 165 MHz limit based on the specification.
+ *
+ * Returns:
+ * Maximum supported TMDS clock rate for the DP dual mode adaptor in kHz.
+ */
+int drm_dp_dual_mode_max_tmds_clock(enum drm_dp_dual_mode_type type,
+				    struct i2c_adapter *adapter)
+{
+	uint8_t max_tmds_clock;
+	ssize_t ret;
+
+	/* native HDMI so no limit */
+	if (type == DRM_DP_DUAL_MODE_NONE)
+		return 0;
+
+	/*
+	 * Type 1 adaptors are limited to 165MHz
+	 * Type 2 adaptors can tells us their limit
+	 */
+	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
+		return 165000;
+
+	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_MAX_TMDS_CLOCK,
+				    &max_tmds_clock, sizeof(max_tmds_clock));
+	if (ret || max_tmds_clock == 0x00 || max_tmds_clock == 0xff)
+		return 165000;
+
+	return max_tmds_clock * 5000 / 2;
+}
+EXPORT_SYMBOL(drm_dp_dual_mode_max_tmds_clock);
+
+/**
+ * drm_dp_dual_mode_get_tmds_output - Get the state of the TMDS output buffers in the DP dual mode adaptor
+ * type: DP dual mode adaptor type
+ * adapter: I2C adapter for the DDC bus
+ * enabled: current state of the TMDS output buffers
+ *
+ * Get the state of the TMDS output buffers in the adaptor. For
+ * type2 adaptors this is queried from the DP_DUAL_MODE_TMDS_OEN
+ * register. As some type 1 adaptors have problems with registers
+ * (see comments in drm_dp_dual_mode_detect()) we don't read the
+ * register on those, instead we simply assume that the buffers
+ * are always enabled.
+ *
+ * Returns:
+ * 0 on success, negative error code on failure
+ */
+int drm_dp_dual_mode_get_tmds_output(enum drm_dp_dual_mode_type type,
+				     struct i2c_adapter *adapter,
+				     bool *enabled)
+{
+	uint8_t tmds_oen;
+	ssize_t ret;
+
+	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI) {
+		*enabled = true;
+		return 0;
+	}
+
+	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_TMDS_OEN,
+				    &tmds_oen, sizeof(tmds_oen));
+	if (ret)
+		return ret;
+
+	*enabled = !(tmds_oen & DP_DUAL_MODE_TMDS_DISABLE);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_dual_mode_get_tmds_output);
+
+/**
+ * drm_dp_dual_mode_set_tmds_output - Enable/disable TMDS output buffers in the DP dual mode adaptor
+ * type: DP dual mode adaptor type
+ * adapter: I2C adapter for the DDC bus
+ * enable: enable (as opposed to disable) the TMDS output buffers
+ *
+ * Set the state of the TMDS output buffers in the adaptor. For
+ * type2 this is set via the DP_DUAL_MODE_TMDS_OEN register. As
+ * some type 1 adaptors have problems with registers (see comments
+ * in drm_dp_dual_mode_detect()) we avoid touching the register,
+ * making this function a no-op on type 1 adaptors.
+ *
+ * Returns:
+ * 0 on success, negative error code on failure
+ */
+int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type,
+				     struct i2c_adapter *adapter, bool enable)
+{
+	uint8_t tmds_oen = enable ? 0 : DP_DUAL_MODE_TMDS_DISABLE;
+	ssize_t ret;
+
+	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
+		return 0;
+
+	ret = drm_dp_dual_mode_write(adapter, DP_DUAL_MODE_TMDS_OEN,
+				     &tmds_oen, sizeof(tmds_oen));
+	if (ret)
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_dual_mode_set_tmds_output);
+
+/**
+ * drm_dp_get_dual_mode_type_name - Get the name of the DP dual mode adaptor type as a string
+ * type: DP dual mode adaptor type
+ *
+ * Returns:
+ * String representation of the DP dual mode adaptor type
+ */
+const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type)
+{
+	switch (type) {
+	case DRM_DP_DUAL_MODE_NONE:
+		return "none";
+	case DRM_DP_DUAL_MODE_TYPE1_DVI:
+		return "type 1 DVI";
+	case DRM_DP_DUAL_MODE_TYPE1_HDMI:
+		return "type 1 HDMI";
+	case DRM_DP_DUAL_MODE_TYPE2_DVI:
+		return "type 2 DVI";
+	case DRM_DP_DUAL_MODE_TYPE2_HDMI:
+		return "type 2 HDMI";
+	default:
+		WARN_ON(type != DRM_DP_DUAL_MODE_UNKNOWN);
+		return "unknown";
+	}
+}
+EXPORT_SYMBOL(drm_dp_get_dual_mode_type_name);
diff --git a/include/drm/drm_dp_dual_mode_helper.h b/include/drm/drm_dp_dual_mode_helper.h
new file mode 100644
index 000000000000..b4603b9fc03d
--- /dev/null
+++ b/include/drm/drm_dp_dual_mode_helper.h
@@ -0,0 +1,83 @@ 
+/*
+ * Copyright © 2016 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef DRM_DP_DUAL_MODE_HELPER_H
+#define DRM_DP_DUAL_MODE_HELPER_H
+
+#include <linux/types.h>
+
+/*
+ * Optional for type 1 DVI adaptors
+ * Mandatory for type 1 HDMI and type 2 adators
+ */
+#define DP_DUAL_MODE_HDMI_ID 0x00 /* 00-0f */
+#define  DP_DUAL_MODE_HDMI_ID_LEN 16
+/*
+ * Optional for type 1 adaptors
+ * Mandatory for type 2 adators
+ */
+#define DP_DUAL_MODE_ADAPTOR_ID 0x10
+#define  DP_DUAL_MODE_REV_MASK 0x07
+#define  DP_DUAL_MODE_REV_TYPE2 0x00
+#define  DP_DUAL_MODE_TYPE_MASK 0xf0
+#define  DP_DUAL_MODE_TYPE_TYPE2 0xa0
+#define DP_DUAL_MODE_IEEE_OUI 0x11 /* 11-13*/
+#define  DP_DUAL_IEEE_OUI_LEN 3
+#define DP_DUAL_DEVICE_ID 0x14 /* 14-19 */
+#define  DP_DUAL_DEVICE_ID_LEN 6
+#define DP_DUAL_MODE_HARDWARE_REV 0x1a
+#define DP_DUAL_MODE_FIRMWARE_MAJOR_REV 0x1b
+#define DP_DUAL_MODE_FIRMWARE_MINOR_REV 0x1c
+#define DP_DUAL_MODE_MAX_TMDS_CLOCK 0x1d
+#define DP_DUAL_MODE_I2C_SPEED_CAP 0x1e
+#define DP_DUAL_MODE_TMDS_OEN 0x20
+#define  DP_DUAL_MODE_TMDS_DISABLE 0x01
+#define DP_DUAL_MODE_HDMI_PIN_CTRL 0x21
+#define  DP_DUAL_MODE_CEC_ENABLE 0x01
+#define DP_DUAL_MODE_I2C_SPEED_CTRL 0x22
+
+struct i2c_adapter;
+
+ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
+			      u8 offset, void *buffer, size_t size);
+ssize_t drm_dp_dual_mode_write(struct i2c_adapter *adapter,
+			       u8 offset, const void *buffer, size_t size);
+
+enum drm_dp_dual_mode_type {
+	DRM_DP_DUAL_MODE_NONE,
+	DRM_DP_DUAL_MODE_UNKNOWN,
+	DRM_DP_DUAL_MODE_TYPE1_DVI,
+	DRM_DP_DUAL_MODE_TYPE1_HDMI,
+	DRM_DP_DUAL_MODE_TYPE2_DVI,
+	DRM_DP_DUAL_MODE_TYPE2_HDMI,
+};
+
+enum drm_dp_dual_mode_type drm_dp_dual_mode_detect(struct i2c_adapter *adapter);
+int drm_dp_dual_mode_max_tmds_clock(enum drm_dp_dual_mode_type type,
+				    struct i2c_adapter *adapter);
+int drm_dp_dual_mode_get_tmds_output(enum drm_dp_dual_mode_type type,
+				     struct i2c_adapter *adapter, bool *enabled);
+int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type,
+				     struct i2c_adapter *adapter, bool enable);
+const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type);
+
+#endif