Re: [PATCH v2 1/2] media: new media controller API for device resource support

[Shuah Khan <shuahkh@osg.samsung.com>]

On 06/03/2015 11:42 AM, Mauro Carvalho Chehab wrote:
> Em Wed, 03 Jun 2015 09:12:53 -0600
> Shuah Khan <shuahkh@osg.samsung.com> escreveu:
> 
>> Add new media controller API to allocate media device as a
>> device resource. When a media device is created on the main
>> struct device which is the parent device for the interface
>> device, it will be available to all drivers associated with
>> that interface. For example, if a usb media device driver
>> creates the media device on the main struct device which is
>> common for all the drivers that control the media device,
>> including the non-media ALSA driver, media controller API
>> can be used to share access to the resources on the media
>> device. This new interface provides the above described
>> feature. A second interface that finds and returns the media
>> device is added to allow drivers to find the media device
>> created by any of the drivers associated with the device.
>>
>> Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
>> ---
>>  drivers/media/media-device.c | 33 +++++++++++++++++++++++++++++++++
>>  include/media/media-device.h |  2 ++
>>  2 files changed, 35 insertions(+)
>>
>> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
>> index 7b39440..a4d5b24 100644
>> --- a/drivers/media/media-device.c
>> +++ b/drivers/media/media-device.c
>> @@ -462,3 +462,36 @@ void media_device_unregister_entity(struct media_entity *entity)
>>  	entity->parent = NULL;
>>  }
>>  EXPORT_SYMBOL_GPL(media_device_unregister_entity);
>> +
>> +static void media_device_release_devres(struct device *dev, void *res)
>> +{
>> +}
>> +
>> +/*
>> + * media_device_get_devres() -	get media device as device resource
>> + *				creates if one doesn't exist
>> +*/
>> +struct media_device *media_device_get_devres(struct device *dev)
>> +{
>> +	struct media_device *mdev;
>> +
>> +	mdev = devres_find(dev, media_device_release_devres, NULL, NULL);
>> +	if (mdev)
>> +		return mdev;
>> +
>> +	mdev = devres_alloc(media_device_release_devres,
>> +				sizeof(struct media_device), GFP_KERNEL);
>> +	if (!mdev)
>> +		return NULL;
>> +	return devres_get(dev, mdev, NULL, NULL);
>> +}
>> +EXPORT_SYMBOL_GPL(media_device_get_devres);
>> +
>> +/*
>> + * media_device_find_devres() - find media device as device resource
>> +*/
>> +struct media_device *media_device_find_devres(struct device *dev)
>> +{
>> +	return devres_find(dev, media_device_release_devres, NULL, NULL);
>> +}
>> +EXPORT_SYMBOL_GPL(media_device_find_devres);
>> diff --git a/include/media/media-device.h b/include/media/media-device.h
>> index 6e6db78..22792cd 100644
>> --- a/include/media/media-device.h
>> +++ b/include/media/media-device.h
>> @@ -95,6 +95,8 @@ void media_device_unregister(struct media_device *mdev);
>>  int __must_check media_device_register_entity(struct media_device *mdev,
>>  					      struct media_entity *entity);
>>  void media_device_unregister_entity(struct media_entity *entity);
>> +struct media_device *media_device_get_devres(struct device *dev);
>> +struct media_device *media_device_find_devres(struct device *dev);
> 
> Hmm... what happens if the Kernel is compiled without MC controller
> support?

Yeah. I noticed media controller api users have the code in ifdef
CONFIG_MEDIA_CONTROLLER.

> 
> I think that the best would be to add a #ifdef at the header file and
> provide an alternate dummy method to avoid the need of testing for it
> everywhere.
> 

I agree with you that a better way to do it would be defining media
controller api in ifdef CONFIG_MEDIA_CONTROLLER and provide stubs for
else case, similar to what I did in sound/usb/media.c

I followed the existing code to add new interfaces. Do you want to see
all media controller interfaces in ifdef clause with stubs or just the
two new interfaces I added? Or is this something that should be done as
a separate change to catch all media controller interfaces?

thanks,
-- Shuah

-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@osg.samsung.com | (970) 217-8978