Re: [PATCH RFC 1/2] [media] v4l2: add V4L2_INPUT_TYPE_DEFAULT

[Hans Verkuil <hverkuil@xs4all.nl>]

On 31/03/17 10:41, Laurent Pinchart wrote:
> Hi Hans,
> 
> On Friday 31 Mar 2017 10:29:04 Hans Verkuil wrote:
>> On 30/03/17 18:02, Helen Koike wrote:
>>> Add V4L2_INPUT_TYPE_DEFAULT and helpers functions for input ioctls to be
>>> used when no inputs are available in the device
>>>
>>> Signed-off-by: Helen Koike <helen.koike@collabora.com>
>>> ---
>>>
>>>  drivers/media/v4l2-core/v4l2-ioctl.c | 27 +++++++++++++++++++++++++++
>>>  include/media/v4l2-ioctl.h           | 26 ++++++++++++++++++++++++++
>>>  include/uapi/linux/videodev2.h       |  1 +
>>>  3 files changed, 54 insertions(+)
>>>
>>> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c
>>> b/drivers/media/v4l2-core/v4l2-ioctl.c index 0c3f238..ccaf04b 100644
>>> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
>>> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
>>> @@ -2573,6 +2573,33 @@ struct mutex *v4l2_ioctl_get_lock(struct
>>> video_device *vdev, unsigned cmd)> 
>>>  	return vdev->lock;
>>>  
>>>  }
>>>
>>> +int v4l2_ioctl_enum_input_default(struct file *file, void *priv,
>>> +				  struct v4l2_input *i)
>>> +{
>>> +	if (i->index > 0)
>>> +		return -EINVAL;
>>> +
>>> +	memset(i, 0, sizeof(*i));
>>> +	i->type = V4L2_INPUT_TYPE_DEFAULT;
>>> +	strlcpy(i->name, "Default", sizeof(i->name));
>>> +
>>> +	return 0;
>>> +}
>>> +EXPORT_SYMBOL(v4l2_ioctl_enum_input_default);
>>> +
>>> +int v4l2_ioctl_g_input_default(struct file *file, void *priv, unsigned
>>> int *i)
>>> +{
>>> +	*i = 0;
>>> +	return 0;
>>> +}
>>> +EXPORT_SYMBOL(v4l2_ioctl_g_input_default);
>>> +
>>> +int v4l2_ioctl_s_input_default(struct file *file, void *priv, unsigned
>>> int i)
>>> +{
>>> +	return i ? -EINVAL : 0;
>>> +}
>>> +EXPORT_SYMBOL(v4l2_ioctl_s_input_default);
>>> +
>>>  /* Common ioctl debug function. This function can be used by
>>>     external ioctl messages as well as internal V4L ioctl */
>>>  void v4l_printk_ioctl(const char *prefix, unsigned int cmd)
>>> diff --git a/include/media/v4l2-ioctl.h b/include/media/v4l2-ioctl.h
>>> index 6cd94e5..accc470 100644
>>> --- a/include/media/v4l2-ioctl.h
>>> +++ b/include/media/v4l2-ioctl.h
>>> @@ -652,6 +652,32 @@ struct video_device;
>>>   */
>>>  
>>>  struct mutex *v4l2_ioctl_get_lock(struct video_device *vdev, unsigned int
>>>  cmd);
>>> +
>>> +/**
>>> + * v4l2_ioctl_enum_input_default - v4l2 ioctl helper for
>>> VIDIOC_ENUM_INPUT ioctl + *
>>> + * Plug this function in vidioc_enum_input field of the struct
>>> v4l2_ioctl_ops to + * enumerate a single input as V4L2_INPUT_TYPE_DEFAULT
>>> + */
>>> +int v4l2_ioctl_enum_input_default(struct file *file, void *priv,
>>> +				  struct v4l2_input *i);
>>> +
>>> +/**
>>> + * v4l2_ioctl_g_input_default - v4l2 ioctl helper for VIDIOC_G_INPUT
>>> ioctl
>>> + *
>>> + * Plug this function in vidioc_g_input field of the struct
>>> v4l2_ioctl_ops
>>> + * when using v4l2_ioctl_enum_input_default
>>> + */
>>> +int v4l2_ioctl_g_input_default(struct file *file, void *priv, unsigned
>>> int *i); +
>>> +/**
>>> + * v4l2_ioctl_s_input_default - v4l2 ioctl helper for VIDIOC_S_INPUT
>>> ioctl
>>> + *
>>> + * Plug this function in vidioc_s_input field of the struct
>>> v4l2_ioctl_ops
>>> + * when using v4l2_ioctl_enum_input_default
>>> + */
>>> +int v4l2_ioctl_s_input_default(struct file *file, void *priv, unsigned
>>> int i); +
>>>
>>>  /* names for fancy debug output */
>>>  extern const char *v4l2_field_names[];
>>>  extern const char *v4l2_type_names[];
>>>
>>> diff --git a/include/uapi/linux/videodev2.h
>>> b/include/uapi/linux/videodev2.h index 316be62..c10bbde 100644
>>> --- a/include/uapi/linux/videodev2.h
>>> +++ b/include/uapi/linux/videodev2.h
>>> @@ -1477,6 +1477,7 @@ struct v4l2_input {
>>>
>>>  };
>>>  
>>>  /*  Values for the 'type' field */
>>>
>>> +#define V4L2_INPUT_TYPE_DEFAULT		0
>>
>> I don't think we should add a new type here. The whole point of this
>> exercise is to allow existing apps to work, and existing apps expect a
>> TYPE_CAMERA.
>>
>> BTW, don't read to much in the term 'CAMERA': it's really a catch all for
>> any video stream, whether it is from a sensor, composite input, HDMI, etc.
>>
>> The description for V4L2_INPUT_TYPE_CAMERA in the spec is hopelessly out of
>> date :-(
>>
>> Rather than creating a new type I would add a new V4L2_IN_CAP_MC capability
>> that indicates that this input is controlled via the media controller. That
>> makes much more sense and it wouldn't potentially break applications.
>>
>> Exactly the same can be done for outputs as well: add V4L2_OUT_CAP_MC and
>> use V4L2_OUTPUT_TYPE_ANALOG as the output type (again, a horrible outdated
>> name and the spec is again out of date).
> 
> What would those capabilities be used for ? Applications can already know 
> whether the MC API is used by a driver. Furthermore, if we really need such a 
> flag, I wouldn't add it at the input/output level but as a video node 
> capability flag.

I have no objection to adding a V4L2_CAP_MC capability instead. In fact, I
think that would be a good idea and better than adding IN/OUT_CAP_MC.

>> Regarding the name: should we use the name stored in struct video_device
>> instead? That might be more descriptive. Alternatively use something like
>> "Media Controller Input".
>>
>> More helpful (perhaps) than just "Default" or "Unknown".
> 
> If the purpose of the name field is to be displayed as-is to the end-user, 
> then "Media Controller Input" is as useless as "Unknown". "Default" would be 
> slightly better.

I would like to have something that indicates to the user that this input is
controlled via the MC. "Default" doesn't do that. I'm honestly not certain
what would be a good description. Frankly, I think that copying the video_device
name might be the better solution here. At least that way the name can actually
map to something sensible.

Regards,

	Hans

> 
>> I'll make a patch to update the input/output type description in the spec.
>>
>>>  #define V4L2_INPUT_TYPE_TUNER		1
>>>  #define V4L2_INPUT_TYPE_CAMERA		2
>>>  #define V4L2_INPUT_TYPE_TOUCH		3
>