Re: Kernel error "Unknown pixelformat 0x00000000" occurs when I start capture video

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Mauro,

On Tuesday, 8 January 2019 20:49:16 EET Mauro Carvalho Chehab wrote:
> Em Tue, 8 Jan 2019 21:11:41 +0500 Mikhail Gavrilov escreveu:
> > On Tue, 8 Jan 2019 at 20:57, Laurent Pinchart wrote:
> >> Thank you.
> >> 
> >> Your device exposes five formats: YUY2 (YUYV), YV12 (YVU420), NV12, P010
> >> and BGR3 (BGR24). They are all supported by V4L2 and the uvcvideo
> >> driver except for the P010 format. This would be easy to fix in the
> >> uvcvideo driver if it wasn't for the fact that the P010 format isn't
> >> support by V4L2. Adding support for it isn't difficult, but I don't
> >> have time to do this myself at the moment. Would you consider
> >> volunteering if I guide you ? :-)
> > 
> > Sure, I'd be happy to help. What is required of me?
> 
> It shouldn't be hard.

Thank you for the detailed and clear explanation.

> First, you need to add the new format at include/uapi/linux/videodev2.h,
> like this one:
> 
> 	#define V4L2_PIX_FMT_YUV420M v4l2_fourcc('Y', 'M', '1', '2') /* 12  YUV420
> planar */
> 
> Please put it together with the other YUV formats.
> 
> As the fourcc "P010" was not used on Linux yet, you could use it,
> e. g., something like:
> 
> 	#define V4L2_PIX_FMT_YUV_P10 v4l2_fourcc('P', '0', '1', '0') /* 10  YUV420
> planar */
> 
> You need then to document it. Each V4L2 format should have a description,
> like this:
> 
> 	https://linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/pixfmt-yuv420m.html
> 
> This is generated via a text file (using ReST syntax). On the above example,
> it is produced by this file:
> 
> 	https://git.linuxtv.org/media_tree.git/tree/Documentation/media/uapi/v4l/pi
> xfmt-yuv420m.rst
> 
> Writing it would take a little more time, but, provided that you don't
> copy what's written from external docs, you could take a look at the
> Internet for the P010 descriptions, and use the pixfmt-yuy420m.rst file
> as the basis for a new pixfmt-p010.rst file.
> 
> This will produce a patch similar to this one:
> 
> 	https://git.linuxtv.org/media_tree.git/commit/?id=5df082e2312c
> 
> Finally, you need to teach the uvc driver that it should report P010
> format, instead of 0x00000000, by adding it at uvc_format_desc uvc_fmts,
> with the corresponding UVC GUID. We usually do this on a separate patch.
> Something like this:
> 
> 	https://git.linuxtv.org/media_tree.git/commit/?id=6ea0d588d35b
> 
> Once you have the patches, submit it to the ML :-)
> 
> You could take a look at the LinuxTV wiki page about how to submit,
> at the developer's section:
> 
> 	https://linuxtv.org/wiki/index.php/Developer_section
> 
> In particular, take a look at "Submitting Your Work" section there.

-- 
Regards,

Laurent Pinchart