Re: [PATCH 1/5] media: videodev2: add Compressed Framebuffer pixel formats

[Helen Koike]

On 6/8/20 6:26 AM, Hans Verkuil wrote:
> On 08/06/2020 10:16, Neil Armstrong wrote:
>> Hi Nicolas,
>>
>> On 05/06/2020 17:35, Nicolas Dufresne wrote:
>>> Le jeudi 04 juin 2020 Ã 15:53 +0200, Neil Armstrong a Ãcrit :
>>>> From: Maxime Jourdan <mjourdan@xxxxxxxxxxxx>
>>>>
>>>> Add two generic Compressed Framebuffer pixel formats to be used
>>>> with a modifier when imported back in another subsystem like DRM/KMS.
>>>>
>>>> These pixel formats represents generic 8bits and 10bits compressed buffers
>>>> with a vendor specific layout.
>>>>
>>>> These are aligned with the DRM_FORMAT_YUV420_8BIT and DRM_FORMAT_YUV420_10BIT
>>>> used to describe the underlying compressed buffers used for ARM Framebuffer
>>>> Compression. In the Amlogic case, the compression is different but the
>>>> underlying buffer components is the same.
>>>>
>>>> Signed-off-by: Maxime Jourdan <mjourdan@xxxxxxxxxxxx>
>>>> Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
>>>> ---
>>>>  drivers/media/v4l2-core/v4l2-ioctl.c | 2 ++
>>>>  include/uapi/linux/videodev2.h       | 9 +++++++++
>>>>  2 files changed, 11 insertions(+)
>>>>
>>>> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
>>>> index 2322f08a98be..8f14adfd5bc5 100644
>>>> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
>>>> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
>>>> @@ -1447,6 +1447,8 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
>>>>  		case V4L2_PIX_FMT_S5C_UYVY_JPG:	descr = "S5C73MX interleaved UYVY/JPEG"; break;
>>>>  		case V4L2_PIX_FMT_MT21C:	descr = "Mediatek Compressed Format"; break;
>>>>  		case V4L2_PIX_FMT_SUNXI_TILED_NV12: descr = "Sunxi Tiled NV12 Format"; break;
>>>> +		case V4L2_PIX_FMT_YUV420_8BIT:	descr = "Compressed YUV 4:2:0 8-bit Format"; break;
>>>> +		case V4L2_PIX_FMT_YUV420_10BIT:	descr = "Compressed YUV 4:2:0 10-bit Format"; break;
>>
>> Seems we are totally on-par with the following :-)
>>
>>>
>>> When I read the DRM documentation [0], I'm reading that YUV420_8BIT
>>> definition matches V4L2_PIX_FMT_YVU420 and V4L2_PIX_FMT_YVU420M fully.
>>> In fact, on DRM side, to represent that format you want to expose here,
>>> they will strictly combine this generic format (documented un-
>>> compressed) with a modifier generated with the macro
>>> DRM_FORMAT_MOD_ARM_AFBC(*). And only the combination represent a unique
>>> and share-able format.
>>
>> Yes, and this is exactly my goal here, and matches the Amlogic Framebuffer as
>> described in patch 4. The modifier patchset is at [1].
>>
>>>
>>> In absence of modifier in V4L2 API, this compressed format should be
>>> named accordingly to the compressed algorithm used (something like
>>> FMT_YUV420_8BIT_AML_FBC). 
>>
>> It's even more complex, the modifier depends on the SoC revision, so we can
>> have up to6 different unique pixel format instead of 2 with a variable
>> modifier.
>>
>>> So I believe these format name cannot be
>>> copied as-is like this, as they can only introduce more ambiguity in
>>> the already quite hard to follow naming of pixel formats. In fact, it
>>> is very common to see multiple different vendor compressions on the
>>> same SoC, so I don't really believe a "generic" compressed format make
>>> sense. To site one, the IMX8M, which got Verrisillicon/Vivante DEC400
>>> on the GPU, and the Hantro G2 compression format. Both will apply to
>>> NV12 class of format so in DRM they would be NV12 + modifier, and the
>>> combination forms the unique format. Now, in term of sharing, they must
>>> be differiented by userspace, as support for compression/decompression
>>> is heterogeneous (in that case the GPU does not support Hantro G2
>>> decompression or compression, and the VPU does not support DEC400).
>>>
>>> I'll remind that the modifier implementation has great value and is
>>> much more scalable then the current V4L2 approach. There has been some
>>> early proposal for this, maybe it's time to prioritize because this
>>> list will starts growing with hundred or even thousands or format,
>>> which is clearly indicated by the increase of modifier generator macro
>>> on the DRM side.
>>
>> Yes, but until the migration of drm_fourcc and v4l2 fourcc into a common one
>> is decided, I'm stuck and this is the only intermediate solution I found.
> 
> We can safely assume that drm fourcc and v4l2 fourcc won't be merged.
> 
> There is too much divergence and not enough interest in creating common
> fourccs.
> 
> But we *do* want to share the modifiers.
> 
>>
>> We have a working solution with Boris's patchset with ext_fmt passing the
>> modifier to user-space.
>>
>> but anyway, since the goal is to merge the fourcc between DRM & V4L2, these YUV420_*BIT
>> will still be needed if we pass the modifier with an extended format struct.
> 
> We tried merging fourccs but that ran into resistance. Frankly, I wouldn't
> bother with this, it is much easier to just create a conversion table in the
> kernel docs.
> 
> So don't block on this, I would really prefer if the ext_fmt series is picked
> up again and rebased and reposted and then worked on.

jfyi, I picked it up, and should post a new version of the RFC soonish.

Regards,
Helen

> The stateless codec support
> is taking less time (it's shaping up well) so there is more time to work on this.
> 
> I believe we really need this since v4l2_buffer and v4l2_format are a real mess.
> 
> Regards,
> 
> 	Hans
> 
>>
>>>
>>>>  		default:
>>>>  			if (fmt->description[0])
>>>>  				return;
>>>> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
>>>> index c3a1cf1c507f..90b9949acb8a 100644
>>>> --- a/include/uapi/linux/videodev2.h
>>>> +++ b/include/uapi/linux/videodev2.h
>>>> @@ -705,6 +705,15 @@ struct v4l2_pix_format {
>>>>  #define V4L2_PIX_FMT_FWHT     v4l2_fourcc('F', 'W', 'H', 'T') /* Fast Walsh Hadamard Transform (vicodec) */
>>>>  #define V4L2_PIX_FMT_FWHT_STATELESS     v4l2_fourcc('S', 'F', 'W', 'H') /* Stateless FWHT (vicodec) */
>>>>  
>>>> +/*
>>>> + * Compressed Luminance+Chrominance meta-formats
>>>> + * In these formats, the component ordering is specified (Y, followed by U
>>>> + * then V), but the exact Linear layout is undefined.
>>>> + * These formats can only be used with a non-Linear modifier.
>>>> + */
>>>> +#define V4L2_PIX_FMT_YUV420_8BIT	v4l2_fourcc('Y', 'U', '0', '8') /* 1-plane YUV 4:2:0 8-bit */
>>>> +#define V4L2_PIX_FMT_YUV420_10BIT	v4l2_fourcc('Y', 'U', '1', '0') /* 1-plane YUV 4:2:0 10-bit */
>>>> +
>>>>  /*  Vendor-specific formats   */
>>>>  #define V4L2_PIX_FMT_CPIA1    v4l2_fourcc('C', 'P', 'I', 'A') /* cpia1 YUV */
>>>>  #define V4L2_PIX_FMT_WNVA     v4l2_fourcc('W', 'N', 'V', 'A') /* Winnov hw compress */
>>>
>>
>> [1] https://patchwork.freedesktop.org/series/73722/#rev7
>>
>