Date:   Fri, 11 Nov 2022 17:13:50 +0800
From:   Hsia-Jun Li <Randy.Li@...aptics.com>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Nicolas Dufresne <nicolas@...fresne.ca>, mchehab@...nel.org,
        hans.verkuil@...co.com, laurent.pinchart@...asonboard.com,
        sakari.ailus@....fi, boris.brezillon@...labora.com,
        hiroh@...omium.org, Brian.Starkey@....com, kernel@...labora.com,
        narmstrong@...libre.com, linux-kernel@...r.kernel.org,
        frkoenig@...omium.org, stanimir.varbanov@...aro.org,
        Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org
Subject: Re: [RFC PATCH v6 02/11] media: v4l2: Extend pixel formats to unify
 single/multi-planar handling (and more)



On 11/11/22 16:52, Tomasz Figa wrote:
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> 
> On Fri, Nov 11, 2022 at 3:31 PM Hsia-Jun Li <Randy.Li@...aptics.com> wrote:
>>
>>
>>
>> On 11/11/22 13:48, Tomasz Figa wrote:
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>>>
>>> On Fri, Nov 11, 2022 at 12:04 PM Hsia-Jun Li <Randy.Li@...aptics.com> wrote:
>>>>
>>>>
>>>>
>>>> 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.
>>>
>>> I feel like this would be only useful in the MMAP mode. Looking at how
>>> the other UAPIs are evolving, things are going towards
>>> userspace-managed allocations, using, for example, DMA-buf heaps. I
>>> think we should follow the trend and keep the MMAP mode just at the
>>> same level of functionality as is today and focus on improvements and
>>> new functionality for the DMABUF mode.
>>>
>> I know there are still some devices(encoder) which only have one
>> register for storing the address of a graphics buffer.
> 
> For those, the legacy MMAP mode (with existing functionality) can be
> successfully used, we wouldn't be removing it any time soon. Just
> don't want to design new functionality specifically for the legacy
> mode.
> 
But it prevents the encoder using the buffer from the outside.
For example, there was an PCI-e interface camera which would write to 
the system memory where is configured to its register, then we would 
like to encode those buffers.
>>>>
>>>> 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://urldefense.proofpoint.com/v2/url?u=https-3A__registry.khronos.org_EGL_extensions_EXT_EGL-5FEXT-5Fimage-5Fdma-5Fbuf-5Fimport-5Fmodifiers.txt&d=DwIFaQ&c=7dfBJ8cXbWjhc0BhImu8wVIoUFmBzj1s88r8EGyM0UY&r=P4xb2_7biqBxD4LGGPrSV6j-jf3C3xlR7PXU-mLTeZE&m=mCebYOAiZK6pbpH1MrZGq-ZkDW-OqORCSwsCEX9ScgdXk_yfWZFJPC5aC93CUg5F&s=rtmW_t2LYoJ6g3Y5wgyICmABu-2Npw3JCOlvUVIYH2o&e=
>>>>
>>>> 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.
>>>
>>> What's an echo plane?
>>>
>> They could be
>> DRM_FORMAT_MOD_SYNA_V4H1_128L128_COMPRESSED
>> DRM_FORMAT_MOD_SYNA_V4H1_128L128_COMPRESSED
>> DRM_FORMAT_MOD_SYNA_MTR
>> DRM_FORMAT_MOD_SYNA_MTR
>> Or
>> DRM_FORMAT_MOD_SYNA_V4H3P8_64L4
>> DRM_FORMAT_MOD_SYNA_V4H3P8_64L4
>>
>> in our platform. It could give a better idea on what is stored in a plane.
> 
> Yes, that's what I was thinking, but my question is more about what
> those planes hold.
DRM_FORMAT_MOD_SYNA_V4H1* or DRM_FORMAT_MOD_SYNA_V4H3P8*
would be the luma and chroma (un)compressed data here. They are 
modifiers to NV12 and NV15.
  Are you sure that they should be planes of the same
> buffer rather than separate buffers?
I am not sure about your question here. I prefer they are in a different 
memory plane. But not all Android APIs support that. If I just think 
about our platform and GNU Linux, I won't care about those limitations.
> 
>>> That said, it indeed looks like we may want to be consistent with DRM
>>> here and allow per-plane modifiers.
>>>
>>>>
>>>> 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.
>>>
>>> Memory allocation doesn't sound to me like it is related to formats or
>>> modifiers in any way. I agree with Nicolas that if we want to allow
>>> the userspace to specify if the memory should be contiguous or not,
>>> that should be a separate flag and actually I'd probably see it in
>>> REQBUF_EXT and CREATE_BUFS_EXT, rather than as a part of the format.
>>>
>> I agree with that. But here is a problem, if there was a display
>> device(DRM) that only supports contiguous planes in a frame buffer.
>> How do we be aware of that?
> 
> That's why I think the MMAP mode is not scalable and shouldn't be
> expanded anymore. Both V4L2 and DRM devices should describe their
> constraints to the userspace and then the userspace should allocate
> accordingly from the right DMA-buf heap. (Or as Android and ChromeOS
> do, just have a central allocator library that understands the
> constraints, so there is no need to query the drivers.)
> 
Because we are working for embedded platforms which don't have memory 
beyond the system memory. I believe those GPU vendors would hate idea of 
DMAheap only.
>>>>
>>>>>
>>>>> 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
>>
>> --
>> Hsia-Jun(Randy) Li

-- 
Hsia-Jun(Randy) Li

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