diff mbox series

[v6,2/2] drm/bridge: hx8837: add a Himax HX8837 display controller driver

Message ID 20201030030800.1036888-3-lkundrak@v3.sk
State New, archived
Headers show
Series [v6,1/2] dt-bindings: display: himax, hx8837: Add Himax HX8837 bindings | expand

Commit Message

Lubomir Rintel Oct. 30, 2020, 3:08 a.m. UTC
Himax HX8837 is used to drive the LCD panel on OLPC platforms.

It controls the panel backlight and is able to refresh it when the LCD
controller (and the rest of the plaform) is powered off.

It also converts regular RGB color data from the LCDC so that it looks
reasonable on the OLPC LCD panel with a monochromatic layer on top of a
layer that can either reflect light (b/w sunlight readable mode) or light
pattern of red, green and blue pixels.

At this point, the driver is rather basic. The self-refresh mode is not
supported. There's no way of independently controlling the color swizzling,
antialiasing or b/w conversion, but it probably isn't too useful either.

There's another driver for the same hardware on OLPC XO-1.5 and XO-1.75
in drivers/staging/olpc_dcon. The display on that hardware doesn't utilize
DRM, so this driver doesn't replace the other one yet.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>

---
Changes since v5:
(All based on feedback from Sam Ravnborg)
- Fix indentation in Kconfig
- Sort #includes
- Use a constant for max brightness instead of a literal
- Remove struct drm_panel from priv data
- Use dev_err() instead of DRM_ERROR
- Replace direct use of backlight props.brightness with
  backlight_get_brightness()
- Document sentinels with { /* sentinel */ }
- Remove unsetting of panel->backlight

Changes since v3:
- Added this patch, in place of a driver derived from
  drivers/staging/olpc_dcon. Compared to the previous one this
  implements the bare minimum, without the fancy stuff such as
  self-refresh that need more work/thinking.

 drivers/gpu/drm/bridge/Kconfig        |  13 +
 drivers/gpu/drm/bridge/Makefile       |   1 +
 drivers/gpu/drm/bridge/himax-hx8837.c | 330 ++++++++++++++++++++++++++
 3 files changed, 344 insertions(+)
 create mode 100644 drivers/gpu/drm/bridge/himax-hx8837.c

Comments

Sam Ravnborg Oct. 31, 2020, 8:01 a.m. UTC | #1
Hi Lubomir.

On Fri, Oct 30, 2020 at 04:08:00AM +0100, Lubomir Rintel wrote:
> Himax HX8837 is used to drive the LCD panel on OLPC platforms.
> 
> It controls the panel backlight and is able to refresh it when the LCD
> controller (and the rest of the plaform) is powered off.
> 
> It also converts regular RGB color data from the LCDC so that it looks
> reasonable on the OLPC LCD panel with a monochromatic layer on top of a
> layer that can either reflect light (b/w sunlight readable mode) or light
> pattern of red, green and blue pixels.
> 
> At this point, the driver is rather basic. The self-refresh mode is not
> supported. There's no way of independently controlling the color swizzling,
> antialiasing or b/w conversion, but it probably isn't too useful either.
> 
> There's another driver for the same hardware on OLPC XO-1.5 and XO-1.75
> in drivers/staging/olpc_dcon. The display on that hardware doesn't utilize
> DRM, so this driver doesn't replace the other one yet.
> 
> Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
> 
> ---
> Changes since v5:
> (All based on feedback from Sam Ravnborg)
> - Fix indentation in Kconfig
> - Sort #includes
> - Use a constant for max brightness instead of a literal
> - Remove struct drm_panel from priv data
> - Use dev_err() instead of DRM_ERROR
> - Replace direct use of backlight props.brightness with
>   backlight_get_brightness()
> - Document sentinels with { /* sentinel */ }
> - Remove unsetting of panel->backlight

Thanks, I missed a few things during the last round, so here is a few
more comments. Only very trivial things but lets get them fixed before
we add the driver to drm-misc-next.

	Sam

> 
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index ef91646441b16..881780719af7c 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -48,6 +48,19 @@ config DRM_DISPLAY_CONNECTOR
>  	  on ARM-based platforms. Saying Y here when this driver is not needed
>  	  will not cause any issue.
>  
> +config DRM_HIMAX_HX8837
> +	tristate "HiMax HX8837 OLPC Display Controller"
> +	depends on OF
> +	depends on OLPC || ARCH_MMP || COMPILE_TEST
> +	select DRM_KMS_HELPER
> +	select BACKLIGHT_LCD_SUPPORT
Unknown symbol - "git grep BACKLIGHT_LCD_SUPPORT" only turned up one
unrelated hit.

> +	select BACKLIGHT_CLASS_DEVICE
Please use a depends - using select on a symbol with a prompt is always
wrong. Yeah, I know you then need to enable backlight to see this
driver. Sorry, but this is the best we can do now.
Many other drivers can cope with depends here.

> +	help
> +	  Enable support for HiMax HX8837 Display Controller as found in the
> +	  OLPC XO laptops.
> +
> +	  If your laptop doesn't have green ears, say "N"
I like this last comment :-)

> +
>  config DRM_LONTIUM_LT9611
>  	tristate "Lontium LT9611 DSI/HDMI bridge"
>  	select SND_SOC_HDMI_CODEC if SND_SOC
> diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
> index 2b3aff104e466..21f72df3260db 100644
> --- a/drivers/gpu/drm/bridge/Makefile
> +++ b/drivers/gpu/drm/bridge/Makefile
> @@ -2,6 +2,7 @@
>  obj-$(CONFIG_DRM_CDNS_DSI) += cdns-dsi.o
>  obj-$(CONFIG_DRM_CHRONTEL_CH7033) += chrontel-ch7033.o
>  obj-$(CONFIG_DRM_DISPLAY_CONNECTOR) += display-connector.o
> +obj-$(CONFIG_DRM_HIMAX_HX8837) += himax-hx8837.o
>  obj-$(CONFIG_DRM_LONTIUM_LT9611) += lontium-lt9611.o
>  obj-$(CONFIG_DRM_LVDS_CODEC) += lvds-codec.o
>  obj-$(CONFIG_DRM_MEGACHIPS_STDPXXXX_GE_B850V3_FW) += megachips-stdpxxxx-ge-b850v3-fw.o
> diff --git a/drivers/gpu/drm/bridge/himax-hx8837.c b/drivers/gpu/drm/bridge/himax-hx8837.c
> new file mode 100644
> index 0000000000000..f472e16cc331d
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/himax-hx8837.c
> @@ -0,0 +1,330 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * HiMax HX8837 Display Controller Driver
> + *
> + * Datasheet: http://wiki.laptop.org/images/0/09/DCON_datasheet_HX8837-A.pdf
> + *
> + * Copyright (C) 2020 Lubomir Rintel
> + */
> +
> +#include <drm/drm_atomic_helper.h>
> +#include <drm/drm_bridge.h>
> +#include <drm/drm_of.h>
> +#include <drm/drm_panel.h>
> +#include <drm/drm_print.h>
drm_print.h is no longer used and should be dropped.

> +#include <drm/drm_probe_helper.h>
> +
> +#include <linux/gpio/consumer.h>
> +#include <linux/module.h>
> +#include <linux/regmap.h>
> +
> +#define bridge_to_hx8837_priv(x) \
> +	container_of(x, struct hx8837_priv, bridge)
> +
> +/* DCON registers */
> +enum {
> +	DCON_REG_ID		= 0x00,
> +	DCON_REG_MODE		= 0x01,
> +	DCON_REG_HRES		= 0x02,
> +	DCON_REG_HTOTAL		= 0x03,
> +	DCON_REG_HSYNC_WIDTH	= 0x04,
> +	DCON_REG_VRES		= 0x05,
> +	DCON_REG_VTOTAL		= 0x06,
> +	DCON_REG_VSYNC_WIDTH	= 0x07,
> +	DCON_REG_TIMEOUT	= 0x08,
> +	DCON_REG_SCAN_INT	= 0x09,
> +	DCON_REG_BRIGHT		= 0x0a,
> +	DCON_REG_MEM_OPT_A	= 0x41,
> +	DCON_REG_MEM_OPT_B	= 0x42,
> +};
> +
> +/* DCON_REG_MODE */
> +enum {
> +	MODE_PASSTHRU		= BIT(0),
> +	MODE_SLEEP		= BIT(1),
> +	MODE_SLEEP_AUTO		= BIT(2),
> +	MODE_BL_ENABLE		= BIT(3),
> +	MODE_BLANK		= BIT(4),
> +	MODE_CSWIZZLE		= BIT(5),
> +	MODE_COL_AA		= BIT(6),
> +	MODE_MONO_LUMA		= BIT(7),
> +	MODE_SCAN_INT		= BIT(8),
> +	MODE_CLOCKDIV		= BIT(9),
> +	MODE_DEBUG		= BIT(14),
> +	MODE_SELFTEST		= BIT(15),
> +};
> +
> +/* DCON_REG_BRIGHT */
> +enum {
> +	BRIGHT_MASK		= GENMASK(7, 0),
> +};
> +
> +struct hx8837_priv {
> +	struct device *dev;
> +	struct regmap *regmap;
> +	struct gpio_desc *load_gpio;
> +
> +	struct drm_bridge *panel_bridge;
> +	struct drm_bridge bridge;
> +};
> +
> +static int hx8837_bridge_attach(struct drm_bridge *bridge,
> +				enum drm_bridge_attach_flags flags)
> +{
> +	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
> +
> +	return drm_bridge_attach(bridge->encoder, priv->panel_bridge,
> +				 bridge, flags);
> +}
> +
> +static enum drm_mode_status hx8837_bridge_mode_valid(
> +				struct drm_bridge *bridge,
> +				const struct drm_display_info *info,
> +				const struct drm_display_mode *mode)
> +{
> +	if (mode->hdisplay > 0xffff)
> +		return MODE_BAD_HVALUE;
> +	if (mode->htotal > 0xffff)
> +		return MODE_BAD_HVALUE;
> +	if (mode->hsync_start - mode->hdisplay > 0xff)
> +		return MODE_HBLANK_WIDE;
> +	if (mode->hsync_end - mode->hsync_start > 0xff)
> +		return MODE_HSYNC_WIDE;
> +	if (mode->vdisplay > 0xffff)
> +		return MODE_BAD_VVALUE;
> +	if (mode->vtotal > 0xffff)
> +		return MODE_BAD_VVALUE;
> +	if (mode->vsync_start - mode->vdisplay > 0xff)
> +		return MODE_VBLANK_WIDE;
> +	if (mode->vsync_end - mode->vsync_start > 0xff)
> +		return MODE_VSYNC_WIDE;
> +
> +	return MODE_OK;
> +}
> +
> +static void hx8837_bridge_disable(struct drm_bridge *bridge)
> +{
> +	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
> +	int ret;
> +
> +	ret = gpiod_direction_output(priv->load_gpio, 0);
> +	if (ret)
> +		dev_err(priv->dev, "error enabling the dcon load: %d\n", ret);
I assume this is disabling the dcon load - so text needs an update

> +
> +	ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,
> +					       MODE_PASSTHRU |
> +					       MODE_SLEEP,
> +					       MODE_PASSTHRU |
> +					       MODE_SLEEP);
> +	if (ret)
> +		dev_err(priv->dev, "error disabling the dcon: %d\n", ret);
> +}
> +
> +static void hx8837_bridge_enable(struct drm_bridge *bridge)
> +{
> +	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
> +	int ret;
> +
> +	ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,
> +					       MODE_PASSTHRU |
> +					       MODE_SLEEP |
> +					       MODE_SLEEP_AUTO |
> +					       MODE_BLANK |
> +					       MODE_SCAN_INT |
> +					       MODE_CLOCKDIV |
> +					       MODE_DEBUG |
> +					       MODE_SELFTEST,
> +					       MODE_PASSTHRU);
> +	if (ret)
> +		dev_err(priv->dev, "error enabling the dcon: %d\n", ret);
> +
> +	ret = gpiod_direction_output(priv->load_gpio, 1);
> +	if (ret)
> +		dev_err(priv->dev, "error enabling the dcon load: %d\n", ret);
> +}
> +
> +static void hx8837_bridge_mode_set(struct drm_bridge *bridge,
> +			   const struct drm_display_mode *mode,
> +			   const struct drm_display_mode *adjusted_mode)
> +{
> +	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
> +
> +	regmap_write(priv->regmap, DCON_REG_HRES, mode->hdisplay);
> +	regmap_write(priv->regmap, DCON_REG_HTOTAL, mode->htotal);
> +	regmap_write(priv->regmap, DCON_REG_HSYNC_WIDTH,
> +			(mode->hsync_start - mode->hdisplay) << 8 |
> +			(mode->hsync_end - mode->hsync_start));
> +	regmap_write(priv->regmap, DCON_REG_VRES, mode->vdisplay);
> +	regmap_write(priv->regmap, DCON_REG_VTOTAL, mode->vtotal);
> +	regmap_write(priv->regmap, DCON_REG_VSYNC_WIDTH,
> +			(mode->vsync_start - mode->vdisplay) << 8 |
> +			(mode->vsync_end - mode->vsync_start));
> +}
> +
> +static const struct drm_bridge_funcs hx8837_bridge_funcs = {
> +	.attach = hx8837_bridge_attach,
> +	.mode_valid = hx8837_bridge_mode_valid,
> +	.disable = hx8837_bridge_disable,
> +	.enable = hx8837_bridge_enable,
> +	.mode_set = hx8837_bridge_mode_set,
> +};
> +
> +static int hx8837_bl_update_status(struct backlight_device *bl)
> +{
> +	struct hx8837_priv *priv = bl_get_data(bl);
> +	unsigned int val;
> +	int ret;
> +
> +	ret = regmap_update_bits(priv->regmap, DCON_REG_BRIGHT,
> +					       BRIGHT_MASK,
> +					       backlight_get_brightness(bl));
> +	if (ret) {
> +		dev_err(&bl->dev, "error setting the backlight: %d\n", ret);
> +		return ret;
> +	}
> +
> +	if (backlight_get_brightness(bl))
> +		val = MODE_CSWIZZLE | MODE_COL_AA;
> +	else
> +		val = MODE_MONO_LUMA;
> +
> +	ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,
> +					       MODE_CSWIZZLE |
> +					       MODE_COL_AA |
> +					       MODE_MONO_LUMA,
> +					       val);
> +	if (ret) {
> +		dev_err(&bl->dev, "error setting color mode: %d\n", ret);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct backlight_ops hx8837_bl_ops = {
> +	.update_status = hx8837_bl_update_status,
> +};
> +
> +static const struct regmap_config hx8837_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 16,
> +	.max_register = 0x4c,
> +	.val_format_endian = REGMAP_ENDIAN_LITTLE,
> +};
> +
> +static int hx8837_probe(struct i2c_client *client,
> +			const struct i2c_device_id *id)
> +{
> +	struct backlight_properties bl_props = {
> +		.type = BACKLIGHT_RAW,
> +		.max_brightness = BRIGHT_MASK,
> +	};
I have recently learned we shall also always set the scale.
This is missing in many drivers - but please do it here.

> +	struct device *dev = &client->dev;
> +	struct backlight_device *bl;
> +	struct hx8837_priv *priv;
> +	struct drm_panel *panel;
> +	unsigned int val;
> +	int ret;
> +
> +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	dev_set_drvdata(dev, priv);
> +	priv->dev = dev;
> +
> +	priv->load_gpio = devm_gpiod_get(dev, "load", GPIOD_ASIS);
> +	if (IS_ERR(priv->load_gpio))
> +		return PTR_ERR(priv->load_gpio);
> +
> +	ret = drm_of_find_panel_or_bridge(dev->of_node, 1, -1, &panel, NULL);
> +	if (ret)
> +		return ret;
> +
> +	if (panel->backlight) {
> +		dev_err(dev, "the panel already has a backlight controller\n");
> +		return -ENODEV;
> +	}
> +
> +	priv->panel_bridge = devm_drm_panel_bridge_add(dev, panel);
> +	if (IS_ERR(priv->panel_bridge))
> +		return PTR_ERR(priv->panel_bridge);
> +
> +	priv->regmap = devm_regmap_init_i2c(client, &hx8837_regmap_config);
> +	if (IS_ERR(priv->regmap)) {
> +		dev_err(dev, "regmap init failed\n");
regmap_init_i2c failed?

> +		return PTR_ERR(priv->regmap);
> +	}
> +
> +	ret = regmap_read(priv->regmap, DCON_REG_ID, &val);
> +	if (ret < 0) {
> +		dev_err(dev, "error reading the model id: %d\n", ret);
> +		return ret;
> +	}
> +	if ((val & 0xff00) != 0xdc00) {
> +		dev_err(dev, "the device is not a hx8837\n");
> +		return -ENODEV;
> +	}
> +
> +	ret = regmap_read(priv->regmap, DCON_REG_BRIGHT, &val);
> +	if (ret < 0) {
> +		dev_err(&bl->dev, "error getting the backlight: %d\n", ret);
> +		return ret;
> +	}
> +	bl_props.brightness = val & 0xf;
> +
> +	bl = devm_backlight_device_register(dev, dev_name(dev), dev, priv,
> +					    &hx8837_bl_ops, &bl_props);
> +	if (IS_ERR(bl)) {
> +		dev_err(dev, "failed to register backlight\n");
> +		return PTR_ERR(bl);
> +	}
> +
> +	panel->backlight = bl;
> +
> +	INIT_LIST_HEAD(&priv->bridge.list);
> +	priv->bridge.funcs = &hx8837_bridge_funcs;
> +	priv->bridge.of_node = dev->of_node;
> +	drm_bridge_add(&priv->bridge);
> +
> +	dev_info(dev, "HiMax HX8837 Display Controller Driver\n");
Debug - not needed
> +	return 0;
> +}
> +
> +static int hx8837_remove(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct hx8837_priv *priv = dev_get_drvdata(dev);
> +
> +	drm_bridge_remove(&priv->bridge);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id hx8837_dt_ids[] = {
> +	{ .compatible = "himax,hx8837", },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, hx8837_dt_ids);
> +
> +static const struct i2c_device_id hx8837_ids[] = {
> +	{ "hx8837", 0 },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(i2c, hx8837_ids);
> +
> +static struct i2c_driver hx8837_driver = {
> +	.probe = hx8837_probe,
> +	.remove = hx8837_remove,
> +	.driver = {
> +		.name = "hx8837",
> +		.of_match_table = of_match_ptr(hx8837_dt_ids),
> +	},
> +	.id_table = hx8837_ids,
> +};
> +
> +module_i2c_driver(hx8837_driver);
> +
> +MODULE_AUTHOR("Lubomir Rintel <lkundrak@v3.sk>");
> +MODULE_DESCRIPTION("HiMax HX8837 Display Controller Driver");
> +MODULE_LICENSE("GPL");
> -- 
> 2.28.0
Lubomir Rintel Oct. 31, 2020, 8:12 p.m. UTC | #2
Hello Sam,

thanks for your response.

On Sat, Oct 31, 2020 at 09:01:37AM +0100, Sam Ravnborg wrote:
> Hi Lubomir.
> 
> On Fri, Oct 30, 2020 at 04:08:00AM +0100, Lubomir Rintel wrote:
> > Himax HX8837 is used to drive the LCD panel on OLPC platforms.
> > 
> > It controls the panel backlight and is able to refresh it when the LCD
> > controller (and the rest of the plaform) is powered off.
> > 
> > It also converts regular RGB color data from the LCDC so that it looks
> > reasonable on the OLPC LCD panel with a monochromatic layer on top of a
> > layer that can either reflect light (b/w sunlight readable mode) or light
> > pattern of red, green and blue pixels.
> > 
> > At this point, the driver is rather basic. The self-refresh mode is not
> > supported. There's no way of independently controlling the color swizzling,
> > antialiasing or b/w conversion, but it probably isn't too useful either.
> > 
> > There's another driver for the same hardware on OLPC XO-1.5 and XO-1.75
> > in drivers/staging/olpc_dcon. The display on that hardware doesn't utilize
> > DRM, so this driver doesn't replace the other one yet.
> > 
> > Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
> > 
> > ---
> > Changes since v5:
> > (All based on feedback from Sam Ravnborg)
> > - Fix indentation in Kconfig
> > - Sort #includes
> > - Use a constant for max brightness instead of a literal
> > - Remove struct drm_panel from priv data
> > - Use dev_err() instead of DRM_ERROR
> > - Replace direct use of backlight props.brightness with
> >   backlight_get_brightness()
> > - Document sentinels with { /* sentinel */ }
> > - Remove unsetting of panel->backlight
> 
> Thanks, I missed a few things during the last round, so here is a few
> more comments. Only very trivial things but lets get them fixed before
> we add the driver to drm-misc-next.
> 
> 	Sam
> 
> > 
> > diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> > index ef91646441b16..881780719af7c 100644
> > --- a/drivers/gpu/drm/bridge/Kconfig
> > +++ b/drivers/gpu/drm/bridge/Kconfig
> > @@ -48,6 +48,19 @@ config DRM_DISPLAY_CONNECTOR
> >  	  on ARM-based platforms. Saying Y here when this driver is not needed
> >  	  will not cause any issue.
> >  
> > +config DRM_HIMAX_HX8837
> > +	tristate "HiMax HX8837 OLPC Display Controller"
> > +	depends on OF
> > +	depends on OLPC || ARCH_MMP || COMPILE_TEST
> > +	select DRM_KMS_HELPER
> > +	select BACKLIGHT_LCD_SUPPORT
> Unknown symbol - "git grep BACKLIGHT_LCD_SUPPORT" only turned up one
> unrelated hit.
> 
> > +	select BACKLIGHT_CLASS_DEVICE
> Please use a depends - using select on a symbol with a prompt is always
> wrong. Yeah, I know you then need to enable backlight to see this
> driver. Sorry, but this is the best we can do now.
> Many other drivers can cope with depends here.

This results in a dependency loop:

  drivers/video/fbdev/Kconfig:12:error: recursive dependency detected!
  drivers/video/fbdev/Kconfig:12: symbol FB is selected by DRM_KMS_FB_HELPER
  drivers/gpu/drm/Kconfig:80:     symbol DRM_KMS_FB_HELPER depends on DRM_KMS_HELPER
  drivers/gpu/drm/Kconfig:74:     symbol DRM_KMS_HELPER is selected by DRM_HIMAX_HX8837
  drivers/gpu/drm/bridge/Kconfig:51:      symbol DRM_HIMAX_HX8837 depends on BACKLIGHT_CLASS_DEVICE
  drivers/video/backlight/Kconfig:143:    symbol BACKLIGHT_CLASS_DEVICE is selected by FB_BACKLIGHT
  drivers/video/fbdev/Kconfig:187:        symbol FB_BACKLIGHT depends on FB

Unfortunately I have no idea how to resolve it at the moment.

I suppose I can look further into it if necessary. Or is it okay if I
leave it at select BACKLIGHT_CLASS_DEVICE for now?
 
> > +	help
> > +	  Enable support for HiMax HX8837 Display Controller as found in the
> > +	  OLPC XO laptops.
> > +
> > +	  If your laptop doesn't have green ears, say "N"
> I like this last comment :-)
> 
> > +
> >  config DRM_LONTIUM_LT9611
> >  	tristate "Lontium LT9611 DSI/HDMI bridge"
> >  	select SND_SOC_HDMI_CODEC if SND_SOC
> > diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
> > index 2b3aff104e466..21f72df3260db 100644
> > --- a/drivers/gpu/drm/bridge/Makefile
> > +++ b/drivers/gpu/drm/bridge/Makefile
> > @@ -2,6 +2,7 @@
> >  obj-$(CONFIG_DRM_CDNS_DSI) += cdns-dsi.o
> >  obj-$(CONFIG_DRM_CHRONTEL_CH7033) += chrontel-ch7033.o
> >  obj-$(CONFIG_DRM_DISPLAY_CONNECTOR) += display-connector.o
> > +obj-$(CONFIG_DRM_HIMAX_HX8837) += himax-hx8837.o
> >  obj-$(CONFIG_DRM_LONTIUM_LT9611) += lontium-lt9611.o
> >  obj-$(CONFIG_DRM_LVDS_CODEC) += lvds-codec.o
> >  obj-$(CONFIG_DRM_MEGACHIPS_STDPXXXX_GE_B850V3_FW) += megachips-stdpxxxx-ge-b850v3-fw.o
> > diff --git a/drivers/gpu/drm/bridge/himax-hx8837.c b/drivers/gpu/drm/bridge/himax-hx8837.c
> > new file mode 100644
> > index 0000000000000..f472e16cc331d
> > --- /dev/null
> > +++ b/drivers/gpu/drm/bridge/himax-hx8837.c
> > @@ -0,0 +1,330 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * HiMax HX8837 Display Controller Driver
> > + *
> > + * Datasheet: http://wiki.laptop.org/images/0/09/DCON_datasheet_HX8837-A.pdf
> > + *
> > + * Copyright (C) 2020 Lubomir Rintel
> > + */
> > +
> > +#include <drm/drm_atomic_helper.h>
> > +#include <drm/drm_bridge.h>
> > +#include <drm/drm_of.h>
> > +#include <drm/drm_panel.h>
> > +#include <drm/drm_print.h>
> drm_print.h is no longer used and should be dropped.
> 
> > +#include <drm/drm_probe_helper.h>
> > +
> > +#include <linux/gpio/consumer.h>
> > +#include <linux/module.h>
> > +#include <linux/regmap.h>
> > +
> > +#define bridge_to_hx8837_priv(x) \
> > +	container_of(x, struct hx8837_priv, bridge)
> > +
> > +/* DCON registers */
> > +enum {
> > +	DCON_REG_ID		= 0x00,
> > +	DCON_REG_MODE		= 0x01,
> > +	DCON_REG_HRES		= 0x02,
> > +	DCON_REG_HTOTAL		= 0x03,
> > +	DCON_REG_HSYNC_WIDTH	= 0x04,
> > +	DCON_REG_VRES		= 0x05,
> > +	DCON_REG_VTOTAL		= 0x06,
> > +	DCON_REG_VSYNC_WIDTH	= 0x07,
> > +	DCON_REG_TIMEOUT	= 0x08,
> > +	DCON_REG_SCAN_INT	= 0x09,
> > +	DCON_REG_BRIGHT		= 0x0a,
> > +	DCON_REG_MEM_OPT_A	= 0x41,
> > +	DCON_REG_MEM_OPT_B	= 0x42,
> > +};
> > +
> > +/* DCON_REG_MODE */
> > +enum {
> > +	MODE_PASSTHRU		= BIT(0),
> > +	MODE_SLEEP		= BIT(1),
> > +	MODE_SLEEP_AUTO		= BIT(2),
> > +	MODE_BL_ENABLE		= BIT(3),
> > +	MODE_BLANK		= BIT(4),
> > +	MODE_CSWIZZLE		= BIT(5),
> > +	MODE_COL_AA		= BIT(6),
> > +	MODE_MONO_LUMA		= BIT(7),
> > +	MODE_SCAN_INT		= BIT(8),
> > +	MODE_CLOCKDIV		= BIT(9),
> > +	MODE_DEBUG		= BIT(14),
> > +	MODE_SELFTEST		= BIT(15),
> > +};
> > +
> > +/* DCON_REG_BRIGHT */
> > +enum {
> > +	BRIGHT_MASK		= GENMASK(7, 0),
> > +};
> > +
> > +struct hx8837_priv {
> > +	struct device *dev;
> > +	struct regmap *regmap;
> > +	struct gpio_desc *load_gpio;
> > +
> > +	struct drm_bridge *panel_bridge;
> > +	struct drm_bridge bridge;
> > +};
> > +
> > +static int hx8837_bridge_attach(struct drm_bridge *bridge,
> > +				enum drm_bridge_attach_flags flags)
> > +{
> > +	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
> > +
> > +	return drm_bridge_attach(bridge->encoder, priv->panel_bridge,
> > +				 bridge, flags);
> > +}
> > +
> > +static enum drm_mode_status hx8837_bridge_mode_valid(
> > +				struct drm_bridge *bridge,
> > +				const struct drm_display_info *info,
> > +				const struct drm_display_mode *mode)
> > +{
> > +	if (mode->hdisplay > 0xffff)
> > +		return MODE_BAD_HVALUE;
> > +	if (mode->htotal > 0xffff)
> > +		return MODE_BAD_HVALUE;
> > +	if (mode->hsync_start - mode->hdisplay > 0xff)
> > +		return MODE_HBLANK_WIDE;
> > +	if (mode->hsync_end - mode->hsync_start > 0xff)
> > +		return MODE_HSYNC_WIDE;
> > +	if (mode->vdisplay > 0xffff)
> > +		return MODE_BAD_VVALUE;
> > +	if (mode->vtotal > 0xffff)
> > +		return MODE_BAD_VVALUE;
> > +	if (mode->vsync_start - mode->vdisplay > 0xff)
> > +		return MODE_VBLANK_WIDE;
> > +	if (mode->vsync_end - mode->vsync_start > 0xff)
> > +		return MODE_VSYNC_WIDE;
> > +
> > +	return MODE_OK;
> > +}
> > +
> > +static void hx8837_bridge_disable(struct drm_bridge *bridge)
> > +{
> > +	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
> > +	int ret;
> > +
> > +	ret = gpiod_direction_output(priv->load_gpio, 0);
> > +	if (ret)
> > +		dev_err(priv->dev, "error enabling the dcon load: %d\n", ret);
> I assume this is disabling the dcon load - so text needs an update
> 
> > +
> > +	ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,
> > +					       MODE_PASSTHRU |
> > +					       MODE_SLEEP,
> > +					       MODE_PASSTHRU |
> > +					       MODE_SLEEP);
> > +	if (ret)
> > +		dev_err(priv->dev, "error disabling the dcon: %d\n", ret);
> > +}
> > +
> > +static void hx8837_bridge_enable(struct drm_bridge *bridge)
> > +{
> > +	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
> > +	int ret;
> > +
> > +	ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,
> > +					       MODE_PASSTHRU |
> > +					       MODE_SLEEP |
> > +					       MODE_SLEEP_AUTO |
> > +					       MODE_BLANK |
> > +					       MODE_SCAN_INT |
> > +					       MODE_CLOCKDIV |
> > +					       MODE_DEBUG |
> > +					       MODE_SELFTEST,
> > +					       MODE_PASSTHRU);
> > +	if (ret)
> > +		dev_err(priv->dev, "error enabling the dcon: %d\n", ret);
> > +
> > +	ret = gpiod_direction_output(priv->load_gpio, 1);
> > +	if (ret)
> > +		dev_err(priv->dev, "error enabling the dcon load: %d\n", ret);
> > +}
> > +
> > +static void hx8837_bridge_mode_set(struct drm_bridge *bridge,
> > +			   const struct drm_display_mode *mode,
> > +			   const struct drm_display_mode *adjusted_mode)
> > +{
> > +	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
> > +
> > +	regmap_write(priv->regmap, DCON_REG_HRES, mode->hdisplay);
> > +	regmap_write(priv->regmap, DCON_REG_HTOTAL, mode->htotal);
> > +	regmap_write(priv->regmap, DCON_REG_HSYNC_WIDTH,
> > +			(mode->hsync_start - mode->hdisplay) << 8 |
> > +			(mode->hsync_end - mode->hsync_start));
> > +	regmap_write(priv->regmap, DCON_REG_VRES, mode->vdisplay);
> > +	regmap_write(priv->regmap, DCON_REG_VTOTAL, mode->vtotal);
> > +	regmap_write(priv->regmap, DCON_REG_VSYNC_WIDTH,
> > +			(mode->vsync_start - mode->vdisplay) << 8 |
> > +			(mode->vsync_end - mode->vsync_start));
> > +}
> > +
> > +static const struct drm_bridge_funcs hx8837_bridge_funcs = {
> > +	.attach = hx8837_bridge_attach,
> > +	.mode_valid = hx8837_bridge_mode_valid,
> > +	.disable = hx8837_bridge_disable,
> > +	.enable = hx8837_bridge_enable,
> > +	.mode_set = hx8837_bridge_mode_set,
> > +};
> > +
> > +static int hx8837_bl_update_status(struct backlight_device *bl)
> > +{
> > +	struct hx8837_priv *priv = bl_get_data(bl);
> > +	unsigned int val;
> > +	int ret;
> > +
> > +	ret = regmap_update_bits(priv->regmap, DCON_REG_BRIGHT,
> > +					       BRIGHT_MASK,
> > +					       backlight_get_brightness(bl));
> > +	if (ret) {
> > +		dev_err(&bl->dev, "error setting the backlight: %d\n", ret);
> > +		return ret;
> > +	}
> > +
> > +	if (backlight_get_brightness(bl))
> > +		val = MODE_CSWIZZLE | MODE_COL_AA;
> > +	else
> > +		val = MODE_MONO_LUMA;
> > +
> > +	ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,
> > +					       MODE_CSWIZZLE |
> > +					       MODE_COL_AA |
> > +					       MODE_MONO_LUMA,
> > +					       val);
> > +	if (ret) {
> > +		dev_err(&bl->dev, "error setting color mode: %d\n", ret);
> > +		return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct backlight_ops hx8837_bl_ops = {
> > +	.update_status = hx8837_bl_update_status,
> > +};
> > +
> > +static const struct regmap_config hx8837_regmap_config = {
> > +	.reg_bits = 8,
> > +	.val_bits = 16,
> > +	.max_register = 0x4c,
> > +	.val_format_endian = REGMAP_ENDIAN_LITTLE,
> > +};
> > +
> > +static int hx8837_probe(struct i2c_client *client,
> > +			const struct i2c_device_id *id)
> > +{
> > +	struct backlight_properties bl_props = {
> > +		.type = BACKLIGHT_RAW,
> > +		.max_brightness = BRIGHT_MASK,
> > +	};
> I have recently learned we shall also always set the scale.
> This is missing in many drivers - but please do it here.
> 
> > +	struct device *dev = &client->dev;
> > +	struct backlight_device *bl;
> > +	struct hx8837_priv *priv;
> > +	struct drm_panel *panel;
> > +	unsigned int val;
> > +	int ret;
> > +
> > +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> > +	if (!priv)
> > +		return -ENOMEM;
> > +
> > +	dev_set_drvdata(dev, priv);
> > +	priv->dev = dev;
> > +
> > +	priv->load_gpio = devm_gpiod_get(dev, "load", GPIOD_ASIS);
> > +	if (IS_ERR(priv->load_gpio))
> > +		return PTR_ERR(priv->load_gpio);
> > +
> > +	ret = drm_of_find_panel_or_bridge(dev->of_node, 1, -1, &panel, NULL);
> > +	if (ret)
> > +		return ret;
> > +
> > +	if (panel->backlight) {
> > +		dev_err(dev, "the panel already has a backlight controller\n");
> > +		return -ENODEV;
> > +	}
> > +
> > +	priv->panel_bridge = devm_drm_panel_bridge_add(dev, panel);
> > +	if (IS_ERR(priv->panel_bridge))
> > +		return PTR_ERR(priv->panel_bridge);
> > +
> > +	priv->regmap = devm_regmap_init_i2c(client, &hx8837_regmap_config);
> > +	if (IS_ERR(priv->regmap)) {
> > +		dev_err(dev, "regmap init failed\n");
> regmap_init_i2c failed?
> 
> > +		return PTR_ERR(priv->regmap);
> > +	}
> > +
> > +	ret = regmap_read(priv->regmap, DCON_REG_ID, &val);
> > +	if (ret < 0) {
> > +		dev_err(dev, "error reading the model id: %d\n", ret);
> > +		return ret;
> > +	}
> > +	if ((val & 0xff00) != 0xdc00) {
> > +		dev_err(dev, "the device is not a hx8837\n");
> > +		return -ENODEV;
> > +	}
> > +
> > +	ret = regmap_read(priv->regmap, DCON_REG_BRIGHT, &val);
> > +	if (ret < 0) {
> > +		dev_err(&bl->dev, "error getting the backlight: %d\n", ret);
> > +		return ret;
> > +	}
> > +	bl_props.brightness = val & 0xf;
> > +
> > +	bl = devm_backlight_device_register(dev, dev_name(dev), dev, priv,
> > +					    &hx8837_bl_ops, &bl_props);
> > +	if (IS_ERR(bl)) {
> > +		dev_err(dev, "failed to register backlight\n");
> > +		return PTR_ERR(bl);
> > +	}
> > +
> > +	panel->backlight = bl;
> > +
> > +	INIT_LIST_HEAD(&priv->bridge.list);
> > +	priv->bridge.funcs = &hx8837_bridge_funcs;
> > +	priv->bridge.of_node = dev->of_node;
> > +	drm_bridge_add(&priv->bridge);
> > +
> > +	dev_info(dev, "HiMax HX8837 Display Controller Driver\n");
> Debug - not needed
> > +	return 0;
> > +}
> > +
> > +static int hx8837_remove(struct i2c_client *client)
> > +{
> > +	struct device *dev = &client->dev;
> > +	struct hx8837_priv *priv = dev_get_drvdata(dev);
> > +
> > +	drm_bridge_remove(&priv->bridge);
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id hx8837_dt_ids[] = {
> > +	{ .compatible = "himax,hx8837", },
> > +	{ /* sentinel */ }
> > +};
> > +MODULE_DEVICE_TABLE(of, hx8837_dt_ids);
> > +
> > +static const struct i2c_device_id hx8837_ids[] = {
> > +	{ "hx8837", 0 },
> > +	{ /* sentinel */ }
> > +};
> > +MODULE_DEVICE_TABLE(i2c, hx8837_ids);
> > +
> > +static struct i2c_driver hx8837_driver = {
> > +	.probe = hx8837_probe,
> > +	.remove = hx8837_remove,
> > +	.driver = {
> > +		.name = "hx8837",
> > +		.of_match_table = of_match_ptr(hx8837_dt_ids),
> > +	},
> > +	.id_table = hx8837_ids,
> > +};
> > +
> > +module_i2c_driver(hx8837_driver);
> > +
> > +MODULE_AUTHOR("Lubomir Rintel <lkundrak@v3.sk>");
> > +MODULE_DESCRIPTION("HiMax HX8837 Display Controller Driver");
> > +MODULE_LICENSE("GPL");
> > -- 
> > 2.28.0
Sam Ravnborg Oct. 31, 2020, 8:56 p.m. UTC | #3
Hi Lubomir.

> > 
> > > +	select BACKLIGHT_CLASS_DEVICE
> > Please use a depends - using select on a symbol with a prompt is always
> > wrong. Yeah, I know you then need to enable backlight to see this
> > driver. Sorry, but this is the best we can do now.
> > Many other drivers can cope with depends here.
> 
> This results in a dependency loop:
> 
>   drivers/video/fbdev/Kconfig:12:error: recursive dependency detected!
>   drivers/video/fbdev/Kconfig:12: symbol FB is selected by DRM_KMS_FB_HELPER
>   drivers/gpu/drm/Kconfig:80:     symbol DRM_KMS_FB_HELPER depends on DRM_KMS_HELPER
>   drivers/gpu/drm/Kconfig:74:     symbol DRM_KMS_HELPER is selected by DRM_HIMAX_HX8837
>   drivers/gpu/drm/bridge/Kconfig:51:      symbol DRM_HIMAX_HX8837 depends on BACKLIGHT_CLASS_DEVICE
>   drivers/video/backlight/Kconfig:143:    symbol BACKLIGHT_CLASS_DEVICE is selected by FB_BACKLIGHT
>   drivers/video/fbdev/Kconfig:187:        symbol FB_BACKLIGHT depends on FB
> 
> Unfortunately I have no idea how to resolve it at the moment.
> 
> I suppose I can look further into it if necessary. Or is it okay if I
> leave it at select BACKLIGHT_CLASS_DEVICE for now?

Sigh, leave it as a select then :-(
The "sigh" is not directed at you but the mess this
BACKLIGHT_CLASS_DEVICE is and the limitations of Kconfig.

	Sam
diff mbox series

Patch

diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
index ef91646441b16..881780719af7c 100644
--- a/drivers/gpu/drm/bridge/Kconfig
+++ b/drivers/gpu/drm/bridge/Kconfig
@@ -48,6 +48,19 @@  config DRM_DISPLAY_CONNECTOR
 	  on ARM-based platforms. Saying Y here when this driver is not needed
 	  will not cause any issue.
 
+config DRM_HIMAX_HX8837
+	tristate "HiMax HX8837 OLPC Display Controller"
+	depends on OF
+	depends on OLPC || ARCH_MMP || COMPILE_TEST
+	select DRM_KMS_HELPER
+	select BACKLIGHT_LCD_SUPPORT
+	select BACKLIGHT_CLASS_DEVICE
+	help
+	  Enable support for HiMax HX8837 Display Controller as found in the
+	  OLPC XO laptops.
+
+	  If your laptop doesn't have green ears, say "N"
+
 config DRM_LONTIUM_LT9611
 	tristate "Lontium LT9611 DSI/HDMI bridge"
 	select SND_SOC_HDMI_CODEC if SND_SOC
diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
index 2b3aff104e466..21f72df3260db 100644
--- a/drivers/gpu/drm/bridge/Makefile
+++ b/drivers/gpu/drm/bridge/Makefile
@@ -2,6 +2,7 @@ 
 obj-$(CONFIG_DRM_CDNS_DSI) += cdns-dsi.o
 obj-$(CONFIG_DRM_CHRONTEL_CH7033) += chrontel-ch7033.o
 obj-$(CONFIG_DRM_DISPLAY_CONNECTOR) += display-connector.o
+obj-$(CONFIG_DRM_HIMAX_HX8837) += himax-hx8837.o
 obj-$(CONFIG_DRM_LONTIUM_LT9611) += lontium-lt9611.o
 obj-$(CONFIG_DRM_LVDS_CODEC) += lvds-codec.o
 obj-$(CONFIG_DRM_MEGACHIPS_STDPXXXX_GE_B850V3_FW) += megachips-stdpxxxx-ge-b850v3-fw.o
diff --git a/drivers/gpu/drm/bridge/himax-hx8837.c b/drivers/gpu/drm/bridge/himax-hx8837.c
new file mode 100644
index 0000000000000..f472e16cc331d
--- /dev/null
+++ b/drivers/gpu/drm/bridge/himax-hx8837.c
@@ -0,0 +1,330 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * HiMax HX8837 Display Controller Driver
+ *
+ * Datasheet: http://wiki.laptop.org/images/0/09/DCON_datasheet_HX8837-A.pdf
+ *
+ * Copyright (C) 2020 Lubomir Rintel
+ */
+
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_bridge.h>
+#include <drm/drm_of.h>
+#include <drm/drm_panel.h>
+#include <drm/drm_print.h>
+#include <drm/drm_probe_helper.h>
+
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+
+#define bridge_to_hx8837_priv(x) \
+	container_of(x, struct hx8837_priv, bridge)
+
+/* DCON registers */
+enum {
+	DCON_REG_ID		= 0x00,
+	DCON_REG_MODE		= 0x01,
+	DCON_REG_HRES		= 0x02,
+	DCON_REG_HTOTAL		= 0x03,
+	DCON_REG_HSYNC_WIDTH	= 0x04,
+	DCON_REG_VRES		= 0x05,
+	DCON_REG_VTOTAL		= 0x06,
+	DCON_REG_VSYNC_WIDTH	= 0x07,
+	DCON_REG_TIMEOUT	= 0x08,
+	DCON_REG_SCAN_INT	= 0x09,
+	DCON_REG_BRIGHT		= 0x0a,
+	DCON_REG_MEM_OPT_A	= 0x41,
+	DCON_REG_MEM_OPT_B	= 0x42,
+};
+
+/* DCON_REG_MODE */
+enum {
+	MODE_PASSTHRU		= BIT(0),
+	MODE_SLEEP		= BIT(1),
+	MODE_SLEEP_AUTO		= BIT(2),
+	MODE_BL_ENABLE		= BIT(3),
+	MODE_BLANK		= BIT(4),
+	MODE_CSWIZZLE		= BIT(5),
+	MODE_COL_AA		= BIT(6),
+	MODE_MONO_LUMA		= BIT(7),
+	MODE_SCAN_INT		= BIT(8),
+	MODE_CLOCKDIV		= BIT(9),
+	MODE_DEBUG		= BIT(14),
+	MODE_SELFTEST		= BIT(15),
+};
+
+/* DCON_REG_BRIGHT */
+enum {
+	BRIGHT_MASK		= GENMASK(7, 0),
+};
+
+struct hx8837_priv {
+	struct device *dev;
+	struct regmap *regmap;
+	struct gpio_desc *load_gpio;
+
+	struct drm_bridge *panel_bridge;
+	struct drm_bridge bridge;
+};
+
+static int hx8837_bridge_attach(struct drm_bridge *bridge,
+				enum drm_bridge_attach_flags flags)
+{
+	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
+
+	return drm_bridge_attach(bridge->encoder, priv->panel_bridge,
+				 bridge, flags);
+}
+
+static enum drm_mode_status hx8837_bridge_mode_valid(
+				struct drm_bridge *bridge,
+				const struct drm_display_info *info,
+				const struct drm_display_mode *mode)
+{
+	if (mode->hdisplay > 0xffff)
+		return MODE_BAD_HVALUE;
+	if (mode->htotal > 0xffff)
+		return MODE_BAD_HVALUE;
+	if (mode->hsync_start - mode->hdisplay > 0xff)
+		return MODE_HBLANK_WIDE;
+	if (mode->hsync_end - mode->hsync_start > 0xff)
+		return MODE_HSYNC_WIDE;
+	if (mode->vdisplay > 0xffff)
+		return MODE_BAD_VVALUE;
+	if (mode->vtotal > 0xffff)
+		return MODE_BAD_VVALUE;
+	if (mode->vsync_start - mode->vdisplay > 0xff)
+		return MODE_VBLANK_WIDE;
+	if (mode->vsync_end - mode->vsync_start > 0xff)
+		return MODE_VSYNC_WIDE;
+
+	return MODE_OK;
+}
+
+static void hx8837_bridge_disable(struct drm_bridge *bridge)
+{
+	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
+	int ret;
+
+	ret = gpiod_direction_output(priv->load_gpio, 0);
+	if (ret)
+		dev_err(priv->dev, "error enabling the dcon load: %d\n", ret);
+
+	ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,
+					       MODE_PASSTHRU |
+					       MODE_SLEEP,
+					       MODE_PASSTHRU |
+					       MODE_SLEEP);
+	if (ret)
+		dev_err(priv->dev, "error disabling the dcon: %d\n", ret);
+}
+
+static void hx8837_bridge_enable(struct drm_bridge *bridge)
+{
+	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
+	int ret;
+
+	ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,
+					       MODE_PASSTHRU |
+					       MODE_SLEEP |
+					       MODE_SLEEP_AUTO |
+					       MODE_BLANK |
+					       MODE_SCAN_INT |
+					       MODE_CLOCKDIV |
+					       MODE_DEBUG |
+					       MODE_SELFTEST,
+					       MODE_PASSTHRU);
+	if (ret)
+		dev_err(priv->dev, "error enabling the dcon: %d\n", ret);
+
+	ret = gpiod_direction_output(priv->load_gpio, 1);
+	if (ret)
+		dev_err(priv->dev, "error enabling the dcon load: %d\n", ret);
+}
+
+static void hx8837_bridge_mode_set(struct drm_bridge *bridge,
+			   const struct drm_display_mode *mode,
+			   const struct drm_display_mode *adjusted_mode)
+{
+	struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
+
+	regmap_write(priv->regmap, DCON_REG_HRES, mode->hdisplay);
+	regmap_write(priv->regmap, DCON_REG_HTOTAL, mode->htotal);
+	regmap_write(priv->regmap, DCON_REG_HSYNC_WIDTH,
+			(mode->hsync_start - mode->hdisplay) << 8 |
+			(mode->hsync_end - mode->hsync_start));
+	regmap_write(priv->regmap, DCON_REG_VRES, mode->vdisplay);
+	regmap_write(priv->regmap, DCON_REG_VTOTAL, mode->vtotal);
+	regmap_write(priv->regmap, DCON_REG_VSYNC_WIDTH,
+			(mode->vsync_start - mode->vdisplay) << 8 |
+			(mode->vsync_end - mode->vsync_start));
+}
+
+static const struct drm_bridge_funcs hx8837_bridge_funcs = {
+	.attach = hx8837_bridge_attach,
+	.mode_valid = hx8837_bridge_mode_valid,
+	.disable = hx8837_bridge_disable,
+	.enable = hx8837_bridge_enable,
+	.mode_set = hx8837_bridge_mode_set,
+};
+
+static int hx8837_bl_update_status(struct backlight_device *bl)
+{
+	struct hx8837_priv *priv = bl_get_data(bl);
+	unsigned int val;
+	int ret;
+
+	ret = regmap_update_bits(priv->regmap, DCON_REG_BRIGHT,
+					       BRIGHT_MASK,
+					       backlight_get_brightness(bl));
+	if (ret) {
+		dev_err(&bl->dev, "error setting the backlight: %d\n", ret);
+		return ret;
+	}
+
+	if (backlight_get_brightness(bl))
+		val = MODE_CSWIZZLE | MODE_COL_AA;
+	else
+		val = MODE_MONO_LUMA;
+
+	ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,
+					       MODE_CSWIZZLE |
+					       MODE_COL_AA |
+					       MODE_MONO_LUMA,
+					       val);
+	if (ret) {
+		dev_err(&bl->dev, "error setting color mode: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static const struct backlight_ops hx8837_bl_ops = {
+	.update_status = hx8837_bl_update_status,
+};
+
+static const struct regmap_config hx8837_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 16,
+	.max_register = 0x4c,
+	.val_format_endian = REGMAP_ENDIAN_LITTLE,
+};
+
+static int hx8837_probe(struct i2c_client *client,
+			const struct i2c_device_id *id)
+{
+	struct backlight_properties bl_props = {
+		.type = BACKLIGHT_RAW,
+		.max_brightness = BRIGHT_MASK,
+	};
+	struct device *dev = &client->dev;
+	struct backlight_device *bl;
+	struct hx8837_priv *priv;
+	struct drm_panel *panel;
+	unsigned int val;
+	int ret;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	dev_set_drvdata(dev, priv);
+	priv->dev = dev;
+
+	priv->load_gpio = devm_gpiod_get(dev, "load", GPIOD_ASIS);
+	if (IS_ERR(priv->load_gpio))
+		return PTR_ERR(priv->load_gpio);
+
+	ret = drm_of_find_panel_or_bridge(dev->of_node, 1, -1, &panel, NULL);
+	if (ret)
+		return ret;
+
+	if (panel->backlight) {
+		dev_err(dev, "the panel already has a backlight controller\n");
+		return -ENODEV;
+	}
+
+	priv->panel_bridge = devm_drm_panel_bridge_add(dev, panel);
+	if (IS_ERR(priv->panel_bridge))
+		return PTR_ERR(priv->panel_bridge);
+
+	priv->regmap = devm_regmap_init_i2c(client, &hx8837_regmap_config);
+	if (IS_ERR(priv->regmap)) {
+		dev_err(dev, "regmap init failed\n");
+		return PTR_ERR(priv->regmap);
+	}
+
+	ret = regmap_read(priv->regmap, DCON_REG_ID, &val);
+	if (ret < 0) {
+		dev_err(dev, "error reading the model id: %d\n", ret);
+		return ret;
+	}
+	if ((val & 0xff00) != 0xdc00) {
+		dev_err(dev, "the device is not a hx8837\n");
+		return -ENODEV;
+	}
+
+	ret = regmap_read(priv->regmap, DCON_REG_BRIGHT, &val);
+	if (ret < 0) {
+		dev_err(&bl->dev, "error getting the backlight: %d\n", ret);
+		return ret;
+	}
+	bl_props.brightness = val & 0xf;
+
+	bl = devm_backlight_device_register(dev, dev_name(dev), dev, priv,
+					    &hx8837_bl_ops, &bl_props);
+	if (IS_ERR(bl)) {
+		dev_err(dev, "failed to register backlight\n");
+		return PTR_ERR(bl);
+	}
+
+	panel->backlight = bl;
+
+	INIT_LIST_HEAD(&priv->bridge.list);
+	priv->bridge.funcs = &hx8837_bridge_funcs;
+	priv->bridge.of_node = dev->of_node;
+	drm_bridge_add(&priv->bridge);
+
+	dev_info(dev, "HiMax HX8837 Display Controller Driver\n");
+	return 0;
+}
+
+static int hx8837_remove(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct hx8837_priv *priv = dev_get_drvdata(dev);
+
+	drm_bridge_remove(&priv->bridge);
+
+	return 0;
+}
+
+static const struct of_device_id hx8837_dt_ids[] = {
+	{ .compatible = "himax,hx8837", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, hx8837_dt_ids);
+
+static const struct i2c_device_id hx8837_ids[] = {
+	{ "hx8837", 0 },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(i2c, hx8837_ids);
+
+static struct i2c_driver hx8837_driver = {
+	.probe = hx8837_probe,
+	.remove = hx8837_remove,
+	.driver = {
+		.name = "hx8837",
+		.of_match_table = of_match_ptr(hx8837_dt_ids),
+	},
+	.id_table = hx8837_ids,
+};
+
+module_i2c_driver(hx8837_driver);
+
+MODULE_AUTHOR("Lubomir Rintel <lkundrak@v3.sk>");
+MODULE_DESCRIPTION("HiMax HX8837 Display Controller Driver");
+MODULE_LICENSE("GPL");