Re: [PATCH] media: usb: uvc: fill in description for unknown pixelformats

[Hans Verkuil <hverkuil@xs4all.nl>]

On 29/03/2023 18:05, Ricardo Ribalda wrote:
> Hi Hans
> 
> Thanks for the patch.
> 
> I believe the user can fetch this info from lsusb, so this is kind of
> duplicated info, and this is why it was removed.

You got to set some description, so using the GUID this seems best.

> Is there an app that uses this unknown format code ? Or the only
> complaint is that WARN() is too loud for the user?

Normally drivers do not pass on unknown formats, but if a driver does,
then I want a WARN. If a driver does this legitimately (and I understand
that's the case for UVC), then the driver should fill in the description
to avoid this WARN.

> 
> Regards!
> 
> On Wed, 29 Mar 2023 at 14:39, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>>
>> If the fcc is 0 (indicating an unknown GUID format), then fill in the
>> description field in ENUM_FMT. Otherwise the V4L2 core will WARN.
>>
>> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
>> Fixes: 50459f103edf ("media: uvcvideo: Remove format descriptions")
>> ---
>> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
>> index 7aefa76a42b3..2f1ced1212cd 100644
>> --- a/drivers/media/usb/uvc/uvc_driver.c
>> +++ b/drivers/media/usb/uvc/uvc_driver.c
>> @@ -256,6 +256,9 @@ static int uvc_parse_format(struct uvc_device *dev,
>>                 } else {
>>                         dev_info(&streaming->intf->dev,
>>                                  "Unknown video format %pUl\n", &buffer[5]);
>> +                       snprintf(format->name, sizeof(format->name), "%pUl\n",
>> +                                &buffer[5]);
> Don't we need at least 38 chars for this?

Yes. But all we have is 31 chars, so we take what we can :-)

This is what uvc did before this was removed.

Regards,

	Hans

> 
> https://docs.kernel.org/core-api/printk-formats.html#uuid-guid-addresses
> 
> 
>> +
>>                         format->fcc = 0;
>>                 }
>>
>> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
>> index 35453f81c1d9..fc6f9e7d8506 100644
>> --- a/drivers/media/usb/uvc/uvc_v4l2.c
>> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
>> @@ -713,6 +713,10 @@ static int uvc_ioctl_enum_fmt(struct uvc_streaming *stream,
>>         if (format->flags & UVC_FMT_FLAG_COMPRESSED)
>>                 fmt->flags |= V4L2_FMT_FLAG_COMPRESSED;
>>         fmt->pixelformat = format->fcc;
>> +       if (format->name[0])
>> +               strscpy(fmt->description, format->name,
>> +                       sizeof(fmt->description));
>> +
>>         return 0;
>>  }
>>
>> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
>> index 9a596c8d894a..22656755a801 100644
>> --- a/drivers/media/usb/uvc/uvcvideo.h
>> +++ b/drivers/media/usb/uvc/uvcvideo.h
>> @@ -264,6 +264,8 @@ struct uvc_format {
>>         u32 fcc;
>>         u32 flags;
>>
>> +       char name[32];
>> +
>>         unsigned int nframes;
>>         struct uvc_frame *frame;
>>  };
>>
> 
> 
> --
> Ricardo Ribalda