Re: [PATCH v3 3/9] DocBook/v4l: Add compressed video formats used on MT8173 codec driver

[Wu-Cheng Li (æåè)]

On Wed, Jul 13, 2016 at 3:14 AM, Nicolas Dufresne
<nicolas.dufresne@xxxxxxxxx> wrote:
> Le mardi 12 juillet 2016 Ã 15:08 -0400, Nicolas Dufresne a Ãcrit :
>> Le mardi 12 juillet 2016 Ã 16:16 +0800, Wu-Cheng Li (æåè) a Ãcrit :
>> > Decoder hardware produces MT21 (compressed). Image processor can
>> > convert it to a format that can be input of display driver.
>> > Tiffany.
>> > When do you plan to upstream image processor (mtk-mdp)?
>> > >
>> > > It can be as input format for encoder, MDP and display drivers in
>> > our
>> > > platform.
>> > I remember display driver can only accept uncompressed MT21. Right?
>> > Basically V4L2_PIX_FMT_MT21 is compressed and is like an opaque
>> > format. It's not usable until it's decompressed and converted by
>> > image
>> > processor.
>>
>> Previously it was described as MediaTek block mode, and now as a
>> MediaTek compressed format. It makes me think you have no idea what
>> this pixel format really is. Is that right ?
>>
>> The main reason why I keep asking, is that we often find similarities
>> between what vendor like to call their proprietary formats. Doing the
>> proper research helps not creating a mess like in Android where you
>> have a lot of formats that all point to the same format. I believe
>> there was the same concern when Samsung wanted to introduce their Z-
>> flip-Z NV12 tile format. In the end they simply provided sufficient
>> documentation so we could document it and implement software
>> converters
>> for test and validation purpose.
>
> Here's the kind of information we want in the documentation.
>
> https://chromium.googlesource.com/chromium/src/media/+/master/base/vide
> o_types.h#40
That is the documentation of decompressed MT21. Originally MT21 was meant
to be a YUV format and we can map it in CPU to use it. The name was changed
to mean a compressed format. The current design is only MTK image processor
can convert it. Software cannot decompress it. I'm not sure if we
should document
the format inside if we cannot decompress in software. For chromium, I'll update
the code to explain MT21 is an opaque compressed format.
>
>   // MediaTek proprietary format. MT21 is similar to NV21 except the memory
>   // layout and pixel layout (swizzles). 12bpp with Y plane followed by a 2x2
>   // interleaved VU plane. Each image contains two buffers -- Y plane and VU
>   // plane. Two planes can be non-contiguous in memory. The starting addresses
>   // of Y plane and VU plane are 4KB alignment.
>   // Suppose image dimension is (width, height). For both Y plane and VU plane:
>   // Row pitch = ((width+15)/16) * 16.
>   // Plane size = Row pitch * (((height+31)/32)*32)
>
> Now obviously this is incomplete, as the swizzling need to be documented of course.
>
>>
>> regards,
>> Nicolas