linux-kernel - Re: [PATCH v10 6/9] media: uapi: Add a control for HANTRO driver

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Date:   Wed, 05 May 2021 16:18:06 +0100
From:   John Cox <jc@...esim.co.uk>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>
Cc:     ezequiel@...labora.com, p.zabel@...gutronix.de, mchehab@...nel.org,
        robh+dt@...nel.org, shawnguo@...nel.org, s.hauer@...gutronix.de,
        festevam@...il.com, lee.jones@...aro.org,
        gregkh@...uxfoundation.org, mripard@...nel.org,
        paul.kocialkowski@...tlin.com, wens@...e.org,
        jernej.skrabec@...l.net, hverkuil-cisco@...all.nl,
        emil.l.velikov@...il.com, kernel@...gutronix.de, linux-imx@....com,
        linux-media@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
        kernel@...labora.com, cphealy@...il.com,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>
Subject: Re: [PATCH v10 6/9] media: uapi: Add a control for HANTRO driver

>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@...labora.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.
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.
> 
> 	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