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From:   John Cox <jc@kynesim.co.uk>
To:     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,
        Benjamin Gaignard <benjamin.gaignard@collabora.com>
Subject: Re: [PATCH v10 6/9] media: uapi: Add a control for HANTRO driver
Date:   Wed, 05 May 2021 16:18:06 +0100
Message-ID: <6bd59glrp4fq3j3ngmbl5p4u7aethvrv34@4ax.com>
References: <20210420121046.181889-1-benjamin.gaignard@collabora.com> <20210420121046.181889-7-benjamin.gaignard@collabora.com>
In-Reply-To: <20210420121046.181889-7-benjamin.gaignard@collabora.com>
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>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
>+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D
>+
>+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.
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"?

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.
>=20
> 	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;
> };
>=20
>+/*  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