On 11/11/22 01:06, Nicolas Dufresne wrote:
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Le samedi 05 novembre 2022 à 23:19 +0800, Hsia-Jun Li a écrit :
VIDIOC_ENUM_EXT_PIX_FMT would report NV12 and NV12M, while
VIDIOC_ENUM_FMT
would just report NV12M.
If NV12 and NV12M are equivalent in Ext API, I don't see why we would
report both (unless I'm missing something, which is probably the case).
The idea was to deprecate the M-variants one day.
I was thinking the way in DRM API is better, always assuming it would
always in a multiple planes. The only problem is we don't have a way to
let the allocator that allocate contiguous memory for planes when we
need to do that.
Its not too late to allow this to be negotiated, but I would move this out of
the pixel format definition to stop the explosion of duplicate pixel formats,
which is a nightmare to deal with.
I wonder whether we need to keep the pixel formats in videodev2.h
anymore. If we would like to use the modifiers from drm_fourcc.h, why
don't we use their pixel formats, they should be the same values of
non-M variant pixel formats of v4l2.
Let videodev2.h only maintain the those codecs or motion based
compressed (pixel) formats.
If I simplify the discussion, we want to
negotiate contiguity with the driver. The new FMT structure should have a
CONTIGUOUS flag. So if userpace sets:
S_FMT(NV12, CONTIGUOUS)
I wonder whether we would allow some planes being contiguous while some
would not. For example, the graphics planes could be in a contiguous
memory address while its compression metadata are not.
Although that is not the case of our platform. I believe it sounds like
reasonable case for improving the performance, two meta planes could
resident in a different memory bank.
That lead to another question which I forgot whether I mention it before.
There are four modifiers in DRM while we would only one in these patches.
From the EGL
https://registry.khronos.org/EGL/extensions/EXT/EGL_EXT_image_dma_buf_import_modifiers.txt
The modifier for echo plane could be different. I wish it would be
better to create a framebuffer being aware of which planes are graphics
or metadata.
I wonder whether it would be better that convincing the DRM maintainer
adding a non vendor flag for contiguous memory allocation here(DRM
itself don't need it).
While whether the memory could be contiguous for these vendor pixel
formats, it is complex vendor defined.
The driver can accepts, and return the unmodified structure, or may drop the
CONTIGUOUS flag, which would mean its not supported. Could be the other way
around too. As for allocation, if you have CONTIGUOUS flag set, userspace does
not have to export or map memory for each planes, as they are the same. We
simply need to define the offset as relative to their allocation, which I think
is the most sensible thing.
Nicolas
--
Hsia-Jun(Randy) Li
