On 09/13/2018 02:46 PM, Hans Verkuil wrote:
On 09/13/18 13:29, Oleksandr Andrushchenko wrote:
Hi, all!
Is there a way in V4L2 to get number of planes from fourcc code
or specifically I need number of planes for a given pixel format
expressed as V4L2_PIX_FMT_* value.
Sadly not. It's part of the documentation for the formats, but there
is no naming scheme through which you can deduce this or even helper
functions for it.
Ok, then I'll probably try to explain what I want to do:
I am implementing a Xen frontend driver which implements
a para-virtual camera protocol [1] which can support
multiple pixel formats. Thus, the driver will support
both single and multi plane formats. For that I need to implement
both single and multi plane format enumerators:
.vidioc_enum_fmt_vid_cap
.vidioc_enum_fmt_vid_cap_mplane
and for .vidioc_enum_fmt_vid_cap I have to filter out of supported
pixel formats those which are multi-planar. So, I hoped I can
use some helper (like DRM provides) to get number of planes for
a given pixel format.
So, it seems that I'll have to code similar table as DRM does
for various V4L2 encoded pixel formats to get num_planes...
I think the main reason why this never happened is that drivers tend to
have custom code for this anyway.
I have proposed in the past that some of this information is exposed
via VIDIOC_ENUM_FMT, but it never got traction.
I know that DRM has such a helper [1], but I am not quite sure
if I can call it with V4L2_PIX_FMT_* as argument to get what I need.
I am a bit confused here because there are different definitions
for DRM [2] and V4L2 [3].
I know. Each subsystem has traditionally been assigning fourccs independently.
In all fairness, this seems to be the case for fourccs throughout the whole
industry.
Regards,
Hans
Thank you,
Oleksandr
[1]
https://elixir.bootlin.com/linux/v4.19-rc3/source/drivers/gpu/drm/drm_fourcc.c#L199
[2]
https://elixir.bootlin.com/linux/v4.19-rc3/source/include/uapi/drm/drm_fourcc.h
[3]
https://elixir.bootlin.com/linux/v4.19-rc3/source/include/uapi/linux/videodev2.h
[1] https://patchwork.kernel.org/patch/10595259/
