Date:   Tue, 9 Jun 2020 07:28:44 -0300
From:   Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     Nicolas Dufresne <nicolas@...fresne.ca>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-media <linux-media@...r.kernel.org>,
        linux-amlogic@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Maxime Jourdan <mjourdan@...libre.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Helen Koike <helen.koike@...labora.com>
Subject: Re: [PATCH 1/5] media: videodev2: add Compressed Framebuffer pixel formats

Adding Helen to the discussion.

On Tue, 9 Jun 2020 at 04:43, Neil Armstrong <narmstrong@...libre.com> wrote:
>
> Hi Nicolas,
>
> On 08/06/2020 20:59, Nicolas Dufresne wrote:
> > Le lundi 08 juin 2020 à 16:43 +0200, Hans Verkuil a écrit :
> >> On 08/06/2020 16:14, Neil Armstrong wrote:
> >>> 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@...libre.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@...libre.com>
> >>>>>>> Signed-off-by: Neil Armstrong <narmstrong@...libre.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 ?
> >>
> >> So to be clear the DRM_FORMAT_YUV420_8BIT/10BIT fourccs define that this is a
> >> buffer containing compressed YUV420 in 8 or 10 bit and the modifier tells userspace
> >> which compression is used, right?
> >>
> >> And we would add V4L2_PIX_FMT_YUV420_8BIT/_10BIT that, I assume, use the same
> >> fourcc values as the DRM variants?
> >>
> >> Since these fourccs are basically useless without V4L2 modifier support it would
> >> only make sense in combination with the ext_fmt series.
> >
> > I personally still think that adding these fourcc will just create a
> > source of confusion and that fourcc should not be tried to be matched
> > at the cost of tripling the already duplicated pixel formats. Userspace
> > already need to implement translation anyway.
>
> By using the same fourcc + modifiers, the translation table would only be needed
> for v4l2-specific fourcc, by reusing the same it's not necessary anymore.
> We have a really simple ffmpeg implementation using ext_fmt, and it makes it
> generic.
>
> >
> > On DRM side, new fourcc was not create for NV12+modifier, I don't see
> > why planar YUV420 has to be different, with or without ext_fmt.
>
> These V4L2_PIX_FMT_YUV420_8BIT/_10BIT were added because of the compressed nature
> of buffers. It's not because of the modifiers, modifiers can be used we any fourcc
> to define vendor specific layout requirements or changes, but for compressed the
> underlying YUV buffer cannot be physically described by any YUV420 fourcc, so
> ARM introduced these fourcc to describe a virtual YUV420 8 or 10bit buffer which
> physical layout is defined by the modifier.
> They could have re-used DRM_FORMAT_YUV420, but it's a 2 plane fourcc, and the other
> describe a true single or multiple plane layout which are simply not true with
> ARM AFBC or Amlogic FBC.
>
> Neil
>
> >
> > Nicolas
> >
> >>
> >> Regards,
> >>
> >>      Hans
> >>
> >>> 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
> >>>>>
> >
>

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