diff mbox

[v5,1/2] drm/dp: Add a drm_aux-dev module for reading/writing dpcd registers.

Message ID 1444427314-1807-2-git-send-email-rafael.antognolli@intel.com (mailing list archive)
State New, archived
Headers show

Commit Message

Rafael Antognolli Oct. 9, 2015, 9:48 p.m. UTC 
This module is heavily based on i2c-dev. Once loaded, it provides one
dev node per DP AUX channel, named drm_dp_auxN, where N is an integer.

It's possible to know which connector owns this aux channel by looking
at the respective sysfs /sys/class/drm_aux_dev/drm_dp_auxN/connector, if
the connector device pointer was correctly set in the aux helper struct.

Two main operations are provided on the registers read and write. The
address of the register to be read or written is given using lseek. The
seek position is updated upon read or write.

Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
---
 drivers/gpu/drm/Kconfig          |   8 +
 drivers/gpu/drm/Makefile         |   1 +
 drivers/gpu/drm/drm_dp_aux_dev.c | 373 +++++++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/drm_dp_helper.c  |   7 +
 include/drm/drm_dp_aux_dev.h     |  50 ++++++
 5 files changed, 439 insertions(+)
 create mode 100644 drivers/gpu/drm/drm_dp_aux_dev.c
 create mode 100644 include/drm/drm_dp_aux_dev.h

Comments

kernel test robot Oct. 10, 2015, 12:49 a.m. UTC | #1 
Hi Rafael,

[auto build test WARNING on drm/drm-next -- if it's inappropriate base, please ignore]

config: mn10300-allyesconfig (attached as .config)
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=mn10300 

All warnings (new ones prefixed by >>):

   In file included from include/linux/list.h:8:0,
                    from include/linux/kobject.h:20,
                    from include/linux/device.h:17,
                    from drivers/gpu/drm/drm_dp_aux_dev.c:28:
   drivers/gpu/drm/drm_dp_aux_dev.c: In function 'auxdev_read':
   include/linux/kernel.h:722:17: warning: comparison of distinct pointer types lacks a cast
     (void) (&_min1 == &_min2);  \
                    ^
>> drivers/gpu/drm/drm_dp_aux_dev.c:180:18: note: in expansion of macro 'min'
      ssize_t todo = min(bytes_pending, sizeof(localbuf));
                     ^
   drivers/gpu/drm/drm_dp_aux_dev.c: In function 'auxdev_write':
   include/linux/kernel.h:722:17: warning: comparison of distinct pointer types lacks a cast
     (void) (&_min1 == &_min2);  \
                    ^
   drivers/gpu/drm/drm_dp_aux_dev.c:220:18: note: in expansion of macro 'min'
      ssize_t todo = min(bytes_pending, sizeof(localbuf));
                     ^

vim +/min +180 drivers/gpu/drm/drm_dp_aux_dev.c

    22	 *
    23	 * Authors:
    24	 *    Rafael Antognolli <rafael.antognolli@intel.com>
    25	 *
    26	 */
    27	
  > 28	#include <linux/device.h>
    29	#include <linux/fs.h>
    30	#include <linux/slab.h>
    31	#include <linux/init.h>
    32	#include <linux/kernel.h>
    33	#include <linux/module.h>
    34	#include <asm/uaccess.h>
    35	#include <drm/drm_dp_helper.h>
    36	#include <drm/drm_crtc.h>
    37	
    38	struct drm_dp_aux_dev {
    39		unsigned index;
    40		struct drm_dp_aux *aux;
    41		struct device *dev;
    42		struct kref refcount;
    43		bool removed;
    44		spinlock_t removed_lock;
    45	};
    46	
    47	#define DRM_AUX_MINORS	256
    48	#define AUX_MAX_OFFSET	(1 << 20)
    49	static DEFINE_IDR(aux_idr);
    50	static DEFINE_SPINLOCK(aux_idr_lock);
    51	static struct class *drm_dp_aux_dev_class;
    52	static int drm_dev_major = -1;
    53	
    54	static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_minor(unsigned index)
    55	{
    56		struct drm_dp_aux_dev *aux_dev = NULL;
    57	
    58		spin_lock(&aux_idr_lock);
    59		aux_dev = idr_find(&aux_idr, index);
    60		if (!kref_get_unless_zero(&aux_dev->refcount))
    61			aux_dev = NULL;
    62		spin_unlock(&aux_idr_lock);
    63	
    64		return aux_dev;
    65	}
    66	
    67	static struct drm_dp_aux_dev *alloc_drm_dp_aux_dev(struct drm_dp_aux *aux)
    68	{
    69		struct drm_dp_aux_dev *aux_dev;
    70		int index;
    71	
    72	
    73		aux_dev = kzalloc(sizeof(*aux_dev), GFP_KERNEL);
    74		if (!aux_dev)
    75			return ERR_PTR(-ENOMEM);
    76		aux_dev->aux = aux;
    77		aux_dev->removed = false;
    78		spin_lock_init(&aux_dev->removed_lock);
    79		kref_init(&aux_dev->refcount);
    80	
    81		idr_preload(GFP_KERNEL);
    82		spin_lock(&aux_idr_lock);
    83		index = idr_alloc_cyclic(&aux_idr, aux_dev, 0, DRM_AUX_MINORS,
    84					 GFP_NOWAIT);
    85		spin_unlock(&aux_idr_lock);
    86		idr_preload_end();
    87		if (index < 0) {
    88			kfree(aux_dev);
    89			return ERR_PTR(-ENOMEM);
    90		}
    91		aux_dev->index = index;
    92	
    93		return aux_dev;
    94	}
    95	
    96	static void free_drm_dp_aux_dev(struct drm_dp_aux_dev *aux_dev)
    97	{
    98		spin_lock(&aux_idr_lock);
    99		idr_remove(&aux_idr, aux_dev->index);
   100		spin_unlock(&aux_idr_lock);
   101		kfree(aux_dev);
   102	}
   103	
   104	static void release_drm_dp_aux_dev(struct kref *ref)
   105	{
   106		int minor;
   107		struct drm_dp_aux_dev *aux_dev =
   108			container_of(ref, struct drm_dp_aux_dev, refcount);
   109		minor = aux_dev->index;
   110		device_destroy(drm_dp_aux_dev_class, MKDEV(drm_dev_major, minor));
   111	
   112		free_drm_dp_aux_dev(aux_dev);
   113	}
   114	
   115	static ssize_t name_show(struct device *dev,
   116				 struct device_attribute *attr, char *buf)
   117	{
   118		ssize_t res;
   119		struct drm_dp_aux_dev *aux_dev =
   120			drm_dp_aux_dev_get_by_minor(MINOR(dev->devt));
   121	
   122		if (!aux_dev)
   123			return -ENODEV;
   124	
   125		res = sprintf(buf, "%s\n", aux_dev->aux->name);
   126		kref_put(&aux_dev->refcount, release_drm_dp_aux_dev);
   127	
   128		return res;
   129	}
   130	static DEVICE_ATTR_RO(name);
   131	
   132	static struct attribute *drm_dp_aux_attrs[] = {
   133		&dev_attr_name.attr,
   134		NULL,
   135	};
   136	ATTRIBUTE_GROUPS(drm_dp_aux);
   137	
   138	static int auxdev_open(struct inode *inode, struct file *file)
   139	{
   140		unsigned int minor = iminor(inode);
   141		struct drm_dp_aux_dev *aux_dev;
   142	
   143		aux_dev = drm_dp_aux_dev_get_by_minor(minor);
   144		if (!aux_dev)
   145			return -ENODEV;
   146	
   147		file->private_data = aux_dev;
   148		return 0;
   149	}
   150	
   151	static loff_t auxdev_llseek(struct file *file, loff_t offset, int whence)
   152	{
   153		return fixed_size_llseek(file, offset, whence, AUX_MAX_OFFSET);
   154	}
   155	
   156	static ssize_t auxdev_read(struct file *file, char __user *buf, size_t count,
   157				   loff_t *offset)
   158	{
   159		size_t bytes_pending, num_bytes_processed = 0;
   160		struct drm_dp_aux_dev *aux_dev = file->private_data;
   161		bool aux_removed;
   162	
   163		if (count < 0)
   164			return -EINVAL;
   165	
   166		spin_lock(&aux_dev->removed_lock);
   167		aux_removed = aux_dev->removed;
   168		spin_unlock(&aux_dev->removed_lock);
   169		if (aux_removed)
   170			return -ENODEV;
   171	
   172		bytes_pending = min((loff_t)count, AUX_MAX_OFFSET - (*offset));
   173	
   174		if (!access_ok(VERIFY_WRITE, buf, bytes_pending))
   175			return -EFAULT;
   176	
   177		while (bytes_pending > 0) {
   178			uint8_t localbuf[DP_AUX_MAX_PAYLOAD_BYTES];
   179			ssize_t res;
 > 180			ssize_t todo = min(bytes_pending, sizeof(localbuf));
   181	
   182			res = drm_dp_dpcd_read(aux_dev->aux, *offset, localbuf, todo);
   183			if (res <= 0)

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
Ville Syrjälä Oct. 20, 2015, 4:05 p.m. UTC | #2 
On Fri, Oct 09, 2015 at 02:48:33PM -0700, Rafael Antognolli wrote:
> This module is heavily based on i2c-dev. Once loaded, it provides one
> dev node per DP AUX channel, named drm_dp_auxN, where N is an integer.
> 
> It's possible to know which connector owns this aux channel by looking
> at the respective sysfs /sys/class/drm_aux_dev/drm_dp_auxN/connector, if
> the connector device pointer was correctly set in the aux helper struct.
> 
> Two main operations are provided on the registers read and write. The
> address of the register to be read or written is given using lseek. The
> seek position is updated upon read or write.
> 
> Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
> ---
>  drivers/gpu/drm/Kconfig          |   8 +
>  drivers/gpu/drm/Makefile         |   1 +
>  drivers/gpu/drm/drm_dp_aux_dev.c | 373 +++++++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_dp_helper.c  |   7 +
>  include/drm/drm_dp_aux_dev.h     |  50 ++++++
>  5 files changed, 439 insertions(+)
>  create mode 100644 drivers/gpu/drm/drm_dp_aux_dev.c
>  create mode 100644 include/drm/drm_dp_aux_dev.h
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 1a0a8df..64fa0f4 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -25,6 +25,14 @@ config DRM_MIPI_DSI
>  	bool
>  	depends on DRM
>  
> +config DRM_DP_AUX_CHARDEV
> +	bool "DRM DP AUX Interface"
> +	depends on DRM
> +	help
> +	  Choose this option to enable a /dev/drm_dp_auxN node that allows to
> +	  read and write values to arbitrary DPCD registers on the DP aux
> +	  channel.
> +
>  config DRM_KMS_HELPER
>  	tristate
>  	depends on DRM
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index e814517..e5bc0ca 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -28,6 +28,7 @@ drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_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
>  drm_kms_helper-$(CONFIG_DRM_KMS_CMA_HELPER) += drm_fb_cma_helper.o
> +drm_kms_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
>  
>  obj-$(CONFIG_DRM_KMS_HELPER) += drm_kms_helper.o
>  
> diff --git a/drivers/gpu/drm/drm_dp_aux_dev.c b/drivers/gpu/drm/drm_dp_aux_dev.c
> new file mode 100644
> index 0000000..a2861e2
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_dp_aux_dev.c
> @@ -0,0 +1,373 @@
> +/*
> + * Copyright © 2015 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 (including the next
> + * paragraph) 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 AUTHORS OR COPYRIGHT HOLDERS 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.
> + *
> + * Authors:
> + *    Rafael Antognolli <rafael.antognolli@intel.com>
> + *
> + */
> +
> +#include <linux/device.h>
> +#include <linux/fs.h>
> +#include <linux/slab.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <asm/uaccess.h>
> +#include <drm/drm_dp_helper.h>
> +#include <drm/drm_crtc.h>
> +
> +struct drm_dp_aux_dev {
> +	unsigned index;
> +	struct drm_dp_aux *aux;
> +	struct device *dev;
> +	struct kref refcount;
> +	bool removed;
> +	spinlock_t removed_lock;
> +};
> +
> +#define DRM_AUX_MINORS	256
> +#define AUX_MAX_OFFSET	(1 << 20)
> +static DEFINE_IDR(aux_idr);
> +static DEFINE_SPINLOCK(aux_idr_lock);
> +static struct class *drm_dp_aux_dev_class;
> +static int drm_dev_major = -1;
> +
> +static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_minor(unsigned index)
> +{
> +	struct drm_dp_aux_dev *aux_dev = NULL;
> +
> +	spin_lock(&aux_idr_lock);
> +	aux_dev = idr_find(&aux_idr, index);
> +	if (!kref_get_unless_zero(&aux_dev->refcount))
> +		aux_dev = NULL;
> +	spin_unlock(&aux_idr_lock);
> +
> +	return aux_dev;
> +}
> +
> +static struct drm_dp_aux_dev *alloc_drm_dp_aux_dev(struct drm_dp_aux *aux)
> +{
> +	struct drm_dp_aux_dev *aux_dev;
> +	int index;
> +
> +
> +	aux_dev = kzalloc(sizeof(*aux_dev), GFP_KERNEL);
> +	if (!aux_dev)
> +		return ERR_PTR(-ENOMEM);
> +	aux_dev->aux = aux;
> +	aux_dev->removed = false;
> +	spin_lock_init(&aux_dev->removed_lock);
> +	kref_init(&aux_dev->refcount);
> +
> +	idr_preload(GFP_KERNEL);
> +	spin_lock(&aux_idr_lock);
> +	index = idr_alloc_cyclic(&aux_idr, aux_dev, 0, DRM_AUX_MINORS,
> +				 GFP_NOWAIT);
> +	spin_unlock(&aux_idr_lock);
> +	idr_preload_end();

With a mutex things would be simpler.

> +	if (index < 0) {
> +		kfree(aux_dev);
> +		return ERR_PTR(-ENOMEM);

Can just pass the error value from idr_alloc_cyclic() upwards I think.

> +	}
> +	aux_dev->index = index;
> +
> +	return aux_dev;
> +}
> +
> +static void free_drm_dp_aux_dev(struct drm_dp_aux_dev *aux_dev)
> +{
> +	spin_lock(&aux_idr_lock);
> +	idr_remove(&aux_idr, aux_dev->index);
> +	spin_unlock(&aux_idr_lock);

I think the idr_remove should be done when unregistering the aux_dev,
that way no one can open it anymore after it's gone.

> +	kfree(aux_dev);
> +}
> +
> +static void release_drm_dp_aux_dev(struct kref *ref)
> +{
> +	int minor;
> +	struct drm_dp_aux_dev *aux_dev =
> +		container_of(ref, struct drm_dp_aux_dev, refcount);
> +	minor = aux_dev->index;
> +	device_destroy(drm_dp_aux_dev_class, MKDEV(drm_dev_major, minor));

device_destroy() should also be done when unregisteing I think.

> +
> +	free_drm_dp_aux_dev(aux_dev);
> +}
> +
> +static ssize_t name_show(struct device *dev,
> +			 struct device_attribute *attr, char *buf)
> +{
> +	ssize_t res;
> +	struct drm_dp_aux_dev *aux_dev =
> +		drm_dp_aux_dev_get_by_minor(MINOR(dev->devt));
> +
> +	if (!aux_dev)
> +		return -ENODEV;
> +
> +	res = sprintf(buf, "%s\n", aux_dev->aux->name);
> +	kref_put(&aux_dev->refcount, release_drm_dp_aux_dev);
> +
> +	return res;
> +}
> +static DEVICE_ATTR_RO(name);
> +
> +static struct attribute *drm_dp_aux_attrs[] = {
> +	&dev_attr_name.attr,
> +	NULL,
> +};
> +ATTRIBUTE_GROUPS(drm_dp_aux);
> +
> +static int auxdev_open(struct inode *inode, struct file *file)
> +{
> +	unsigned int minor = iminor(inode);
> +	struct drm_dp_aux_dev *aux_dev;
> +
> +	aux_dev = drm_dp_aux_dev_get_by_minor(minor);
> +	if (!aux_dev)
> +		return -ENODEV;
> +
> +	file->private_data = aux_dev;
> +	return 0;
> +}
> +
> +static loff_t auxdev_llseek(struct file *file, loff_t offset, int whence)
> +{
> +	return fixed_size_llseek(file, offset, whence, AUX_MAX_OFFSET);
> +}
> +
> +static ssize_t auxdev_read(struct file *file, char __user *buf, size_t count,
> +			   loff_t *offset)
> +{
> +	size_t bytes_pending, num_bytes_processed = 0;
> +	struct drm_dp_aux_dev *aux_dev = file->private_data;
> +	bool aux_removed;
> +
> +	if (count < 0)
> +		return -EINVAL;
> +
> +	spin_lock(&aux_dev->removed_lock);
> +	aux_removed = aux_dev->removed;
> +	spin_unlock(&aux_dev->removed_lock);
> +	if (aux_removed)
> +		return -ENODEV;

Hmm. This seems racy still. aux_dev will now stay around until the file
is closed, but the actual aux helper backing it may still disappear at
any time. I don't think we want to hold a lock around the whole thing,
cause I have a feeling that way lies lockdep issues. So maybe we need
some kinda atomic use counter here, or something?

read()
{
	if (atomic_inc_unless_zero(usecount))
		return -...;

	...

	atomic_dec();
	wake_up();
}

unregister()
{
	idr_remove();
	atomic_dec(usecount);
	wait_event(usecount == 0);
	kref_put();
}

register()
{
	...
	atomic_set(usecount, 1);
	idr_alloc_cyclic();
}

I guess another option would to just wait for all fds to be closed in a
similar fashion. But that seems like a more open ended wait.

> +
> +	bytes_pending = min((loff_t)count, AUX_MAX_OFFSET - (*offset));
> +
> +	if (!access_ok(VERIFY_WRITE, buf, bytes_pending))
> +		return -EFAULT;
> +
> +	while (bytes_pending > 0) {
> +		uint8_t localbuf[DP_AUX_MAX_PAYLOAD_BYTES];
> +		ssize_t res;
> +		ssize_t todo = min(bytes_pending, sizeof(localbuf));
> +
> +		res = drm_dp_dpcd_read(aux_dev->aux, *offset, localbuf, todo);
> +		if (res <= 0)
> +			return num_bytes_processed ? num_bytes_processed : res;
> +		if (__copy_to_user(buf + num_bytes_processed, localbuf, res))
> +			return num_bytes_processed ?
> +				num_bytes_processed : -EFAULT;
> +		bytes_pending -= res;
> +		*offset += res;
> +		num_bytes_processed += res;
> +	}
> +
> +	return num_bytes_processed;
> +}
> +
> +static ssize_t auxdev_write(struct file *file, const char __user *buf,
> +			    size_t count, loff_t *offset)
> +{
> +	size_t bytes_pending, num_bytes_processed = 0;
> +	struct drm_dp_aux_dev *aux_dev = file->private_data;
> +	bool aux_removed;
> +
> +	if (count < 0)
> +		return -EINVAL;
> +
> +	spin_lock(&aux_dev->removed_lock);
> +	aux_removed = aux_dev->removed;
> +	spin_unlock(&aux_dev->removed_lock);
> +	if (aux_removed)
> +		return -ENODEV;
> +
> +	bytes_pending = min((loff_t)count, AUX_MAX_OFFSET - *offset);
> +
> +	if (!access_ok(VERIFY_READ, buf, bytes_pending))
> +		return -EFAULT;
> +
> +	while (bytes_pending > 0) {
> +		uint8_t localbuf[DP_AUX_MAX_PAYLOAD_BYTES];
> +		ssize_t res;
> +		ssize_t todo = min(bytes_pending, sizeof(localbuf));
> +
> +		if (__copy_from_user(localbuf,
> +				     buf + num_bytes_processed, todo)) {
> +			return num_bytes_processed ?
> +				num_bytes_processed : -EFAULT;
> +		}
> +
> +		res = drm_dp_dpcd_write(aux_dev->aux, *offset, localbuf, todo);
> +		if (res <= 0) {
> +			return num_bytes_processed ? num_bytes_processed : res;
> +		}
> +		bytes_pending -= res;
> +		*offset += res;
> +		num_bytes_processed += res;
> +	}
> +
> +	return num_bytes_processed;
> +}
> +
> +static int auxdev_release(struct inode *inode, struct file *file)
> +{
> +	struct drm_dp_aux_dev *aux_dev = file->private_data;
> +	kref_put(&aux_dev->refcount, release_drm_dp_aux_dev);
> +	return 0;
> +}
> +
> +static const struct file_operations auxdev_fops = {
> +	.owner		= THIS_MODULE,
> +	.llseek		= auxdev_llseek,
> +	.read		= auxdev_read,
> +	.write		= auxdev_write,
> +	.open		= auxdev_open,
> +	.release	= auxdev_release,
> +};
> +
> +#define to_auxdev(d) container_of(d, struct drm_dp_aux_dev, aux)
> +
> +/**
> + * drm_dp_aux_register_devnode() - register a devnode for this aux channel
> + * @aux: DisplayPort AUX channel
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_aux_register_devnode(struct drm_dp_aux *aux)
> +{
> +	struct drm_dp_aux_dev *aux_dev;
> +	int res;
> +
> +	aux_dev = alloc_drm_dp_aux_dev(aux);
> +	if (IS_ERR(aux_dev))
> +		return PTR_ERR(aux_dev);
> +
> +	aux_dev->dev = device_create(drm_dp_aux_dev_class, aux->dev,
> +				     MKDEV(drm_dev_major, aux_dev->index), NULL,
> +				     "drm_dp_aux%d", aux_dev->index);
> +	if (IS_ERR(aux_dev->dev)) {
> +		res = PTR_ERR(aux_dev->dev);
> +		goto error;
> +	}
> +
> +	pr_debug("drm_dp_aux_dev: aux [%s] registered as minor %d\n",
> +		 aux->name, aux_dev->index);
> +	return 0;
> +error:
> +	free_drm_dp_aux_dev(aux_dev);
> +	return res;
> +}
> +EXPORT_SYMBOL(drm_dp_aux_register_devnode);
> +
> +static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_aux(struct drm_dp_aux *aux)
> +{
> +	struct drm_dp_aux_dev *iter, *aux_dev = NULL;
> +	int id;
> +
> +	/* don't increase kref count here because this function should only be
> +	 * used by drm_dp_aux_unregister_devnode. Thus, it will always have at
> +	 * least one reference - the one that drm_dp_aux_register_devnode
> +	 * created */
> +	spin_lock(&aux_idr_lock);
> +	idr_for_each_entry(&aux_idr, iter, id) {
> +		if (iter->aux == aux) {
> +			aux_dev = iter;
> +			break;
> +		}
> +	}
> +	spin_unlock(&aux_idr_lock);
> +	return aux_dev;
> +}
> +
> +/**
> + * drm_dp_aux_unregister_devnode() - unregister a devnode for this aux channel
> + * @aux: DisplayPort AUX channel
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux)
> +{
> +	struct drm_dp_aux_dev *aux_dev;
> +
> +	aux_dev = drm_dp_aux_dev_get_by_aux(aux);
> +	if (!aux_dev) /* attach must have failed */
> +		return 0;
> +
> +	spin_lock(&aux_dev->removed_lock);
> +	aux_dev->removed = true;
> +	spin_unlock(&aux_dev->removed_lock);
> +
> +	kref_put(&aux_dev->refcount, release_drm_dp_aux_dev);
> +	pr_debug("drm_dp_aux_dev: aux [%s] unregistered\n", aux->name);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_aux_unregister_devnode);
> +
> +static int __init drm_dp_aux_dev_init(void)
> +{
> +	int res;
> +
> +	res = register_chrdev(0, "aux", &auxdev_fops);

As soon as this returns someone can open the device, so seems like this
should be the last thing we do.

> +	if (res < 0)
> +		goto out;
> +	drm_dev_major = res;
> +
> +	drm_dp_aux_dev_class = class_create(THIS_MODULE, "drm_dp_aux_dev");
> +	if (IS_ERR(drm_dp_aux_dev_class)) {
> +		res = PTR_ERR(drm_dp_aux_dev_class);
> +		goto out_unreg_chrdev;
> +	}
> +	drm_dp_aux_dev_class->dev_groups = drm_dp_aux_groups;
> +
> +	idr_init(&aux_idr);

AFAIK no need to init it since you used DEFINE_IDR()

> +
> +	return 0;
> +
> +out_unreg_chrdev:
> +	unregister_chrdev(drm_dev_major, "aux");
> +out:
> +	printk(KERN_ERR "%s: Driver Initialisation failed\n", __FILE__);
> +	return res;
> +}
> +
> +static void __exit drm_dp_aux_dev_exit(void)
> +{
> +	class_destroy(drm_dp_aux_dev_class);
> +	unregister_chrdev(drm_dev_major, "aux");
> +}
> +
> +MODULE_AUTHOR("Rafael Antognolli <rafael.antognolli@intel.com>");
> +MODULE_DESCRIPTION("DRM DP AUX /dev entries driver");
> +MODULE_LICENSE("GPL and additional rights");
> +
> +module_init(drm_dp_aux_dev_init);
> +module_exit(drm_dp_aux_dev_exit);
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 9535c5b..e50f65d 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -28,6 +28,7 @@
>  #include <linux/sched.h>
>  #include <linux/i2c.h>
>  #include <drm/drm_dp_helper.h>
> +#include <drm/drm_dp_aux_dev.h>
>  #include <drm/drmP.h>
>  
>  /**
> @@ -768,6 +769,11 @@ int drm_dp_aux_register(struct drm_dp_aux *aux)
>  	strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(aux->dev),
>  		sizeof(aux->ddc.name));
>  
> +

Looks like an extra newline we don't need.

> +	if (drm_dp_aux_register_devnode(aux))
> +		printk(KERN_ERR "%s: Could not register drm_dp_aux_dev.\n",
> +		       __FILE__);
> +
>  	return i2c_add_adapter(&aux->ddc);
>  }
>  EXPORT_SYMBOL(drm_dp_aux_register);
> @@ -778,6 +784,7 @@ EXPORT_SYMBOL(drm_dp_aux_register);
>   */
>  void drm_dp_aux_unregister(struct drm_dp_aux *aux)
>  {
> +	drm_dp_aux_unregister_devnode(aux);
>  	i2c_del_adapter(&aux->ddc);
>  }
>  EXPORT_SYMBOL(drm_dp_aux_unregister);
> diff --git a/include/drm/drm_dp_aux_dev.h b/include/drm/drm_dp_aux_dev.h
> new file mode 100644
> index 0000000..35409a2
> --- /dev/null
> +++ b/include/drm/drm_dp_aux_dev.h
> @@ -0,0 +1,50 @@
> +/*
> + * Copyright © 2015 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 (including the next
> + * paragraph) 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 AUTHORS OR COPYRIGHT HOLDERS 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.
> + *
> + * Authors:
> + *    Rafael Antognolli <rafael.antognolli@intel.com>
> + *
> + */
> +
> +#ifndef DRM_DP_AUX_DEV
> +#define DRM_DP_AUX_DEV
> +
> +#ifdef CONFIG_DRM_DP_AUX_CHARDEV
> +
> +int drm_dp_aux_register_devnode(struct drm_dp_aux *aux);
> +int drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux);
> +
> +#else
> +
> +static inline int drm_dp_aux_register_devnode(struct drm_dp_aux *aux)
> +{
> +	return 0;
> +}
> +
> +static inline int drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux)
> +{
> +	return 0;
> +}
> +
> +#endif
> +
> +#endif
> -- 
> 2.4.3
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel
diff mbox

Patch

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 1a0a8df..64fa0f4 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -25,6 +25,14 @@  config DRM_MIPI_DSI
 	bool
 	depends on DRM
 
+config DRM_DP_AUX_CHARDEV
+	bool "DRM DP AUX Interface"
+	depends on DRM
+	help
+	  Choose this option to enable a /dev/drm_dp_auxN node that allows to
+	  read and write values to arbitrary DPCD registers on the DP aux
+	  channel.
+
 config DRM_KMS_HELPER
 	tristate
 	depends on DRM
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index e814517..e5bc0ca 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -28,6 +28,7 @@  drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_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
 drm_kms_helper-$(CONFIG_DRM_KMS_CMA_HELPER) += drm_fb_cma_helper.o
+drm_kms_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
 
 obj-$(CONFIG_DRM_KMS_HELPER) += drm_kms_helper.o
 
diff --git a/drivers/gpu/drm/drm_dp_aux_dev.c b/drivers/gpu/drm/drm_dp_aux_dev.c
new file mode 100644
index 0000000..a2861e2
--- /dev/null
+++ b/drivers/gpu/drm/drm_dp_aux_dev.c
@@ -0,0 +1,373 @@ 
+/*
+ * Copyright © 2015 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 (including the next
+ * paragraph) 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 AUTHORS OR COPYRIGHT HOLDERS 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.
+ *
+ * Authors:
+ *    Rafael Antognolli <rafael.antognolli@intel.com>
+ *
+ */
+
+#include <linux/device.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <asm/uaccess.h>
+#include <drm/drm_dp_helper.h>
+#include <drm/drm_crtc.h>
+
+struct drm_dp_aux_dev {
+	unsigned index;
+	struct drm_dp_aux *aux;
+	struct device *dev;
+	struct kref refcount;
+	bool removed;
+	spinlock_t removed_lock;
+};
+
+#define DRM_AUX_MINORS	256
+#define AUX_MAX_OFFSET	(1 << 20)
+static DEFINE_IDR(aux_idr);
+static DEFINE_SPINLOCK(aux_idr_lock);
+static struct class *drm_dp_aux_dev_class;
+static int drm_dev_major = -1;
+
+static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_minor(unsigned index)
+{
+	struct drm_dp_aux_dev *aux_dev = NULL;
+
+	spin_lock(&aux_idr_lock);
+	aux_dev = idr_find(&aux_idr, index);
+	if (!kref_get_unless_zero(&aux_dev->refcount))
+		aux_dev = NULL;
+	spin_unlock(&aux_idr_lock);
+
+	return aux_dev;
+}
+
+static struct drm_dp_aux_dev *alloc_drm_dp_aux_dev(struct drm_dp_aux *aux)
+{
+	struct drm_dp_aux_dev *aux_dev;
+	int index;
+
+
+	aux_dev = kzalloc(sizeof(*aux_dev), GFP_KERNEL);
+	if (!aux_dev)
+		return ERR_PTR(-ENOMEM);
+	aux_dev->aux = aux;
+	aux_dev->removed = false;
+	spin_lock_init(&aux_dev->removed_lock);
+	kref_init(&aux_dev->refcount);
+
+	idr_preload(GFP_KERNEL);
+	spin_lock(&aux_idr_lock);
+	index = idr_alloc_cyclic(&aux_idr, aux_dev, 0, DRM_AUX_MINORS,
+				 GFP_NOWAIT);
+	spin_unlock(&aux_idr_lock);
+	idr_preload_end();
+	if (index < 0) {
+		kfree(aux_dev);
+		return ERR_PTR(-ENOMEM);
+	}
+	aux_dev->index = index;
+
+	return aux_dev;
+}
+
+static void free_drm_dp_aux_dev(struct drm_dp_aux_dev *aux_dev)
+{
+	spin_lock(&aux_idr_lock);
+	idr_remove(&aux_idr, aux_dev->index);
+	spin_unlock(&aux_idr_lock);
+	kfree(aux_dev);
+}
+
+static void release_drm_dp_aux_dev(struct kref *ref)
+{
+	int minor;
+	struct drm_dp_aux_dev *aux_dev =
+		container_of(ref, struct drm_dp_aux_dev, refcount);
+	minor = aux_dev->index;
+	device_destroy(drm_dp_aux_dev_class, MKDEV(drm_dev_major, minor));
+
+	free_drm_dp_aux_dev(aux_dev);
+}
+
+static ssize_t name_show(struct device *dev,
+			 struct device_attribute *attr, char *buf)
+{
+	ssize_t res;
+	struct drm_dp_aux_dev *aux_dev =
+		drm_dp_aux_dev_get_by_minor(MINOR(dev->devt));
+
+	if (!aux_dev)
+		return -ENODEV;
+
+	res = sprintf(buf, "%s\n", aux_dev->aux->name);
+	kref_put(&aux_dev->refcount, release_drm_dp_aux_dev);
+
+	return res;
+}
+static DEVICE_ATTR_RO(name);
+
+static struct attribute *drm_dp_aux_attrs[] = {
+	&dev_attr_name.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(drm_dp_aux);
+
+static int auxdev_open(struct inode *inode, struct file *file)
+{
+	unsigned int minor = iminor(inode);
+	struct drm_dp_aux_dev *aux_dev;
+
+	aux_dev = drm_dp_aux_dev_get_by_minor(minor);
+	if (!aux_dev)
+		return -ENODEV;
+
+	file->private_data = aux_dev;
+	return 0;
+}
+
+static loff_t auxdev_llseek(struct file *file, loff_t offset, int whence)
+{
+	return fixed_size_llseek(file, offset, whence, AUX_MAX_OFFSET);
+}
+
+static ssize_t auxdev_read(struct file *file, char __user *buf, size_t count,
+			   loff_t *offset)
+{
+	size_t bytes_pending, num_bytes_processed = 0;
+	struct drm_dp_aux_dev *aux_dev = file->private_data;
+	bool aux_removed;
+
+	if (count < 0)
+		return -EINVAL;
+
+	spin_lock(&aux_dev->removed_lock);
+	aux_removed = aux_dev->removed;
+	spin_unlock(&aux_dev->removed_lock);
+	if (aux_removed)
+		return -ENODEV;
+
+	bytes_pending = min((loff_t)count, AUX_MAX_OFFSET - (*offset));
+
+	if (!access_ok(VERIFY_WRITE, buf, bytes_pending))
+		return -EFAULT;
+
+	while (bytes_pending > 0) {
+		uint8_t localbuf[DP_AUX_MAX_PAYLOAD_BYTES];
+		ssize_t res;
+		ssize_t todo = min(bytes_pending, sizeof(localbuf));
+
+		res = drm_dp_dpcd_read(aux_dev->aux, *offset, localbuf, todo);
+		if (res <= 0)
+			return num_bytes_processed ? num_bytes_processed : res;
+		if (__copy_to_user(buf + num_bytes_processed, localbuf, res))
+			return num_bytes_processed ?
+				num_bytes_processed : -EFAULT;
+		bytes_pending -= res;
+		*offset += res;
+		num_bytes_processed += res;
+	}
+
+	return num_bytes_processed;
+}
+
+static ssize_t auxdev_write(struct file *file, const char __user *buf,
+			    size_t count, loff_t *offset)
+{
+	size_t bytes_pending, num_bytes_processed = 0;
+	struct drm_dp_aux_dev *aux_dev = file->private_data;
+	bool aux_removed;
+
+	if (count < 0)
+		return -EINVAL;
+
+	spin_lock(&aux_dev->removed_lock);
+	aux_removed = aux_dev->removed;
+	spin_unlock(&aux_dev->removed_lock);
+	if (aux_removed)
+		return -ENODEV;
+
+	bytes_pending = min((loff_t)count, AUX_MAX_OFFSET - *offset);
+
+	if (!access_ok(VERIFY_READ, buf, bytes_pending))
+		return -EFAULT;
+
+	while (bytes_pending > 0) {
+		uint8_t localbuf[DP_AUX_MAX_PAYLOAD_BYTES];
+		ssize_t res;
+		ssize_t todo = min(bytes_pending, sizeof(localbuf));
+
+		if (__copy_from_user(localbuf,
+				     buf + num_bytes_processed, todo)) {
+			return num_bytes_processed ?
+				num_bytes_processed : -EFAULT;
+		}
+
+		res = drm_dp_dpcd_write(aux_dev->aux, *offset, localbuf, todo);
+		if (res <= 0) {
+			return num_bytes_processed ? num_bytes_processed : res;
+		}
+		bytes_pending -= res;
+		*offset += res;
+		num_bytes_processed += res;
+	}
+
+	return num_bytes_processed;
+}
+
+static int auxdev_release(struct inode *inode, struct file *file)
+{
+	struct drm_dp_aux_dev *aux_dev = file->private_data;
+	kref_put(&aux_dev->refcount, release_drm_dp_aux_dev);
+	return 0;
+}
+
+static const struct file_operations auxdev_fops = {
+	.owner		= THIS_MODULE,
+	.llseek		= auxdev_llseek,
+	.read		= auxdev_read,
+	.write		= auxdev_write,
+	.open		= auxdev_open,
+	.release	= auxdev_release,
+};
+
+#define to_auxdev(d) container_of(d, struct drm_dp_aux_dev, aux)
+
+/**
+ * drm_dp_aux_register_devnode() - register a devnode for this aux channel
+ * @aux: DisplayPort AUX channel
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_aux_register_devnode(struct drm_dp_aux *aux)
+{
+	struct drm_dp_aux_dev *aux_dev;
+	int res;
+
+	aux_dev = alloc_drm_dp_aux_dev(aux);
+	if (IS_ERR(aux_dev))
+		return PTR_ERR(aux_dev);
+
+	aux_dev->dev = device_create(drm_dp_aux_dev_class, aux->dev,
+				     MKDEV(drm_dev_major, aux_dev->index), NULL,
+				     "drm_dp_aux%d", aux_dev->index);
+	if (IS_ERR(aux_dev->dev)) {
+		res = PTR_ERR(aux_dev->dev);
+		goto error;
+	}
+
+	pr_debug("drm_dp_aux_dev: aux [%s] registered as minor %d\n",
+		 aux->name, aux_dev->index);
+	return 0;
+error:
+	free_drm_dp_aux_dev(aux_dev);
+	return res;
+}
+EXPORT_SYMBOL(drm_dp_aux_register_devnode);
+
+static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_aux(struct drm_dp_aux *aux)
+{
+	struct drm_dp_aux_dev *iter, *aux_dev = NULL;
+	int id;
+
+	/* don't increase kref count here because this function should only be
+	 * used by drm_dp_aux_unregister_devnode. Thus, it will always have at
+	 * least one reference - the one that drm_dp_aux_register_devnode
+	 * created */
+	spin_lock(&aux_idr_lock);
+	idr_for_each_entry(&aux_idr, iter, id) {
+		if (iter->aux == aux) {
+			aux_dev = iter;
+			break;
+		}
+	}
+	spin_unlock(&aux_idr_lock);
+	return aux_dev;
+}
+
+/**
+ * drm_dp_aux_unregister_devnode() - unregister a devnode for this aux channel
+ * @aux: DisplayPort AUX channel
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux)
+{
+	struct drm_dp_aux_dev *aux_dev;
+
+	aux_dev = drm_dp_aux_dev_get_by_aux(aux);
+	if (!aux_dev) /* attach must have failed */
+		return 0;
+
+	spin_lock(&aux_dev->removed_lock);
+	aux_dev->removed = true;
+	spin_unlock(&aux_dev->removed_lock);
+
+	kref_put(&aux_dev->refcount, release_drm_dp_aux_dev);
+	pr_debug("drm_dp_aux_dev: aux [%s] unregistered\n", aux->name);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_aux_unregister_devnode);
+
+static int __init drm_dp_aux_dev_init(void)
+{
+	int res;
+
+	res = register_chrdev(0, "aux", &auxdev_fops);
+	if (res < 0)
+		goto out;
+	drm_dev_major = res;
+
+	drm_dp_aux_dev_class = class_create(THIS_MODULE, "drm_dp_aux_dev");
+	if (IS_ERR(drm_dp_aux_dev_class)) {
+		res = PTR_ERR(drm_dp_aux_dev_class);
+		goto out_unreg_chrdev;
+	}
+	drm_dp_aux_dev_class->dev_groups = drm_dp_aux_groups;
+
+	idr_init(&aux_idr);
+
+	return 0;
+
+out_unreg_chrdev:
+	unregister_chrdev(drm_dev_major, "aux");
+out:
+	printk(KERN_ERR "%s: Driver Initialisation failed\n", __FILE__);
+	return res;
+}
+
+static void __exit drm_dp_aux_dev_exit(void)
+{
+	class_destroy(drm_dp_aux_dev_class);
+	unregister_chrdev(drm_dev_major, "aux");
+}
+
+MODULE_AUTHOR("Rafael Antognolli <rafael.antognolli@intel.com>");
+MODULE_DESCRIPTION("DRM DP AUX /dev entries driver");
+MODULE_LICENSE("GPL and additional rights");
+
+module_init(drm_dp_aux_dev_init);
+module_exit(drm_dp_aux_dev_exit);
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 9535c5b..e50f65d 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -28,6 +28,7 @@ 
 #include <linux/sched.h>
 #include <linux/i2c.h>
 #include <drm/drm_dp_helper.h>
+#include <drm/drm_dp_aux_dev.h>
 #include <drm/drmP.h>
 
 /**
@@ -768,6 +769,11 @@  int drm_dp_aux_register(struct drm_dp_aux *aux)
 	strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(aux->dev),
 		sizeof(aux->ddc.name));
 
+
+	if (drm_dp_aux_register_devnode(aux))
+		printk(KERN_ERR "%s: Could not register drm_dp_aux_dev.\n",
+		       __FILE__);
+
 	return i2c_add_adapter(&aux->ddc);
 }
 EXPORT_SYMBOL(drm_dp_aux_register);
@@ -778,6 +784,7 @@  EXPORT_SYMBOL(drm_dp_aux_register);
  */
 void drm_dp_aux_unregister(struct drm_dp_aux *aux)
 {
+	drm_dp_aux_unregister_devnode(aux);
 	i2c_del_adapter(&aux->ddc);
 }
 EXPORT_SYMBOL(drm_dp_aux_unregister);
diff --git a/include/drm/drm_dp_aux_dev.h b/include/drm/drm_dp_aux_dev.h
new file mode 100644
index 0000000..35409a2
--- /dev/null
+++ b/include/drm/drm_dp_aux_dev.h
@@ -0,0 +1,50 @@ 
+/*
+ * Copyright © 2015 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 (including the next
+ * paragraph) 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 AUTHORS OR COPYRIGHT HOLDERS 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.
+ *
+ * Authors:
+ *    Rafael Antognolli <rafael.antognolli@intel.com>
+ *
+ */
+
+#ifndef DRM_DP_AUX_DEV
+#define DRM_DP_AUX_DEV
+
+#ifdef CONFIG_DRM_DP_AUX_CHARDEV
+
+int drm_dp_aux_register_devnode(struct drm_dp_aux *aux);
+int drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux);
+
+#else
+
+static inline int drm_dp_aux_register_devnode(struct drm_dp_aux *aux)
+{
+	return 0;
+}
+
+static inline int drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux)
+{
+	return 0;
+}
+
+#endif
+
+#endif