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Subject: Re: [PATCH 1/5] media: videodev2: add Compressed Framebuffer pixel
 formats
To:     Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Nicolas Dufresne <nicolas@ndufresne.ca>
Cc:     linux-media@vger.kernel.org, linux-amlogic@lists.infradead.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Maxime Jourdan <mjourdan@baylibre.com>,
        Tomasz Figa <tfiga@chromium.org>
References: <20200604135317.9235-1-narmstrong@baylibre.com>
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 <a15dea55-3ca4-2a65-5c56-6c1edd2de405@xs4all.nl>
From:   Neil Armstrong <narmstrong@baylibre.com>
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Date:   Mon, 8 Jun 2020 16:14:39 +0200
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On 08/06/2020 11:26, 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 à 15:53 +0200, Neil Armstrong a écrit :
>>>> From: Maxime Jourdan <mjourdan@baylibre.com>
>>>>
>>>> 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@baylibre.com>
>>>> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
>>>> ---
>>>>  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;

[..]

>>>
>>> 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. The stateless codec support
> is taking less time (it's shaping up well) so there is more time to work on this.

Ok, I already starting discussing with Helen Koike about the ext_fnt re-spin.

Should I re-introduce different v4l2 pixfmt for these DRM YUV420_*BIT or I can keep this
patch along the new ext_fmt and shared modifiers ?

Neil

> 
> 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
>>
>