linux-kernel - Re: [PATCH v5 1/8] drm/fourcc: Add modifier definitions for describing Amlogic Video Framebuffer Compression

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Date:   Fri, 17 Apr 2020 18:11:52 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     dri-devel@...ts.freedesktop.org, linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Kevin Hilman <khilman@...libre.com>
Subject: Re: [PATCH v5 1/8] drm/fourcc: Add modifier definitions for
 describing Amlogic Video Framebuffer Compression

On 17/04/2020 18:05, Neil Armstrong wrote:
> On 17/04/2020 17:07, Daniel Vetter wrote:
>> On Thu, Apr 16, 2020 at 05:24:53PM +0200, Neil Armstrong wrote:
>>> Amlogic uses a proprietary lossless image compression protocol and format
>>> for their hardware video codec accelerators, either video decoders or
>>> video input encoders.
>>>
>>> It considerably reduces memory bandwidth while writing and reading
>>> frames in memory.
>>>
>>> The underlying storage is considered to be 3 components, 8bit or 10-bit
>>> per component, YCbCr 420, single plane :
>>> - DRM_FORMAT_YUV420_8BIT
>>> - DRM_FORMAT_YUV420_10BIT
>>>
>>> This modifier will be notably added to DMA-BUF frames imported from the V4L2
>>> Amlogic VDEC decoder.
>>>
>>> This introduces the basic layout composed of:
>>> - a body content organized in 64x32 superblocks with 4096 bytes per
>>>   superblock in default mode.
>>> - a 32 bytes per 128x64 header block
>>>
>>> This layout is tranferrable between Amlogic SoCs supporting this modifier.
>>>
>>> Tested-by: Kevin Hilman <khilman@...libre.com>
>>> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
>>> ---
>>>  include/uapi/drm/drm_fourcc.h | 39 +++++++++++++++++++++++++++++++++++
>>>  1 file changed, 39 insertions(+)
>>>
>>> diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
>>> index 8bc0b31597d8..a1b163a5641f 100644
>>> --- a/include/uapi/drm/drm_fourcc.h
>>> +++ b/include/uapi/drm/drm_fourcc.h
>>> @@ -309,6 +309,7 @@ extern "C" {
>>>  #define DRM_FORMAT_MOD_VENDOR_BROADCOM 0x07
>>>  #define DRM_FORMAT_MOD_VENDOR_ARM     0x08
>>>  #define DRM_FORMAT_MOD_VENDOR_ALLWINNER 0x09
>>> +#define DRM_FORMAT_MOD_VENDOR_AMLOGIC 0x0a
>>>  
>>>  /* add more to the end as needed */
>>>  
>>> @@ -804,6 +805,44 @@ extern "C" {
>>>   */
>>>  #define DRM_FORMAT_MOD_ALLWINNER_TILED fourcc_mod_code(ALLWINNER, 1)
>>>  
>>> +/*
>>> + * Amlogic Video Framebuffer Compression modifiers
>>> + *
>>> + * Amlogic uses a proprietary lossless image compression protocol and format
>>> + * for their hardware video codec accelerators, either video decoders or
>>> + * video input encoders.
>>> + *
>>> + * It considerably reduces memory bandwidth while writing and reading
>>> + * frames in memory.
>>> + *
>>> + * The underlying storage is considered to be 3 components, 8bit or 10-bit
>>> + * per component YCbCr 420, single plane :
>>> + * - DRM_FORMAT_YUV420_8BIT
>>> + * - DRM_FORMAT_YUV420_10BIT
>>> + *
>>> + * The first 8 bits of the mode defines the layout, then the following 8 bits
>>> + * defines the options changing the layout.
>>
>> None of the modifiers you're doing seem to have these other 8 bits
>> defined anywhere. And it's not encoded in your modifiers. Can't we just
>> enumerate the ones we have/need and done?
> 
> It's introduced in patch 5

I did slit the options/layout for the last one: SCATTER so I could apply the BASIC and the option
first then continue the discussion on the second SCATTER layout.

So maybe I should add the option in the first patch.

Neil