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Subject: Re: [PATCH v10 6/9] media: uapi: Add a control for HANTRO driver
From:   Nicolas Dufresne <nicolas@ndufresne.ca>
To:     John Cox <jc@kynesim.co.uk>,
        Benjamin Gaignard <benjamin.gaignard@collabora.com>
Cc:     ezequiel@collabora.com, p.zabel@pengutronix.de, mchehab@kernel.org,
        robh+dt@kernel.org, shawnguo@kernel.org, s.hauer@pengutronix.de,
        festevam@gmail.com, lee.jones@linaro.org,
        gregkh@linuxfoundation.org, mripard@kernel.org,
        paul.kocialkowski@bootlin.com, wens@csie.org,
        jernej.skrabec@siol.net, hverkuil-cisco@xs4all.nl,
        emil.l.velikov@gmail.com, kernel@pengutronix.de, linux-imx@nxp.com,
        linux-media@vger.kernel.org, linux-rockchip@lists.infradead.org,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org,
        kernel@collabora.com, cphealy@gmail.com
Date:   Wed, 05 May 2021 11:33:24 -0400
In-Reply-To: <6bd59glrp4fq3j3ngmbl5p4u7aethvrv34@4ax.com>
References: <20210420121046.181889-1-benjamin.gaignard@collabora.com>
         <20210420121046.181889-7-benjamin.gaignard@collabora.com>
         <6bd59glrp4fq3j3ngmbl5p4u7aethvrv34@4ax.com>
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Le mercredi 05 mai 2021 à 16:18 +0100, John Cox a écrit :
> > The HEVC HANTRO driver needs to know the number of bits to skip at
> > the beginning of the slice header.
> > That is a hardware specific requirement so create a dedicated control
> > for this purpose.
> > 
> > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
> > ---
> > .../userspace-api/media/drivers/hantro.rst    | 19 +++++++++++++++++++
> > .../userspace-api/media/drivers/index.rst     |  1 +
> > include/media/hevc-ctrls.h                    | 13 +++++++++++++
> > 3 files changed, 33 insertions(+)
> > create mode 100644 Documentation/userspace-api/media/drivers/hantro.rst
> > 
> > diff --git a/Documentation/userspace-api/media/drivers/hantro.rst
> > b/Documentation/userspace-api/media/drivers/hantro.rst
> > new file mode 100644
> > index 000000000000..cd9754b4e005
> > --- /dev/null
> > +++ b/Documentation/userspace-api/media/drivers/hantro.rst
> > @@ -0,0 +1,19 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +Hantro video decoder driver
> > +===========================
> > +
> > +The Hantro video decoder driver implements the following driver-specific
> > controls:
> > +
> > +``V4L2_CID_HANTRO_HEVC_SLICE_HEADER_SKIP (integer)``
> > +    Specifies to Hantro HEVC video decoder driver the number of data (in
> > bits) to
> > +    skip in the slice segment header.
> > +    If non-IDR, the bits to be skipped go from syntax element
> > "pic_output_flag"
> > +    to before syntax element "slice_temporal_mvp_enabled_flag".
> > +    If IDR, the skipped bits are just "pic_output_flag"
> > +    (separate_colour_plane_flag is not supported).
> 
> What happens if it is a dependant_slice_segement or
> output_flag_present_flag?  Those flags are all dependant on
> dependant_slice_segement being false.  I'm guessing 0 but it maybe
> should be documented.

Zero indeed.

> Likewise if output_flag_present_flag is false pic_output_flag will not
> be coded, so maybe express it as "after slice_type" rather than "before
> pic_output_flag"?

Should work too.

> 
> Regards
> 
> John Cox
> 
> > +.. note::
> > +
> > +        This control is not yet part of the public kernel API and
> > +        it is expected to change.
> > diff --git a/Documentation/userspace-api/media/drivers/index.rst
> > b/Documentation/userspace-api/media/drivers/index.rst
> > index 1a9038f5f9fa..12e3c512d718 100644
> > --- a/Documentation/userspace-api/media/drivers/index.rst
> > +++ b/Documentation/userspace-api/media/drivers/index.rst
> > @@ -33,6 +33,7 @@ For more details see the file COPYING in the source
> > distribution of Linux.
> > 
> > 	ccs
> > 	cx2341x-uapi
> > +        hantro
> > 	imx-uapi
> > 	max2175
> > 	meye-uapi
> > diff --git a/include/media/hevc-ctrls.h b/include/media/hevc-ctrls.h
> > index 8e0109eea454..b713eeed1915 100644
> > --- a/include/media/hevc-ctrls.h
> > +++ b/include/media/hevc-ctrls.h
> > @@ -224,4 +224,17 @@ struct v4l2_ctrl_hevc_decode_params {
> > 	__u64	flags;
> > };
> > 
> > +/*  MPEG-class control IDs specific to the Hantro driver as defined by V4L2
> > */
> > +#define
> > V4L2_CID_CODEC_HANTRO_BASE				(V4L2_CTRL_CLASS_CODEC | 0x1200)
> > +/*
> > + * V4L2_CID_HANTRO_HEVC_SLICE_HEADER_SKIP -
> > + * the number of data (in bits) to skip in the
> > + * slice segment header.
> > + * If non-IDR, the bits to be skipped go from syntax element
> > "pic_output_flag"
> > + * to before syntax element "slice_temporal_mvp_enabled_flag".
> > + * If IDR, the skipped bits are just "pic_output_flag"
> > + * (separate_colour_plane_flag is not supported).
> > + */
> > +#define V4L2_CID_HANTRO_HEVC_SLICE_HEADER_SKIP	(V4L2_CID_CODEC_HANTRO_BASE
> > + 0)
> > +
> > #endif