linux-kernel - [PATCH v2 2/4] media: docs: dev-decoder: Trigger dynamic source change for colorspace

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Message-ID: <20250117061938.3923516-2-ming.qian@oss.nxp.com>
Date: Fri, 17 Jan 2025 15:19:36 +0900
From: Ming Qian <ming.qian@....nxp.com>
To: mchehab@...nel.org,
	hverkuil-cisco@...all.nl
Cc: nicolas@...fresne.ca,
	shawnguo@...nel.org,
	robh+dt@...nel.org,
	s.hauer@...gutronix.de,
	kernel@...gutronix.de,
	festevam@...il.com,
	linux-imx@....com,
	xiahong.bao@....com,
	eagle.zhou@....com,
	tao.jiang_2@....com,
	ming.qian@....nxp.com,
	imx@...ts.linux.dev,
	linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: [PATCH v2 2/4] media: docs: dev-decoder: Trigger dynamic source change for colorspace

If colorspace changes, the client needs to renegotiate the pipeline,
otherwise the decoded frame may not be displayed correctly.

When a colorspace change in the stream, the decoder sends a
V4L2_EVENT_SOURCE_CHANGE event with changes set to
V4L2_EVENT_SRC_CH_COLORSPACE. After client receive this source change
event, then client can switch to the correct stream setting. And each
frame can be displayed properly.

So add colorspace as a trigger parameter for dynamic resolution change.

Signed-off-by: Ming Qian <ming.qian@....nxp.com>
---
v2
- Add V4L2_EVENT_SRC_CH_COLORSPACE for colorspace source change event

 .../userspace-api/media/v4l/dev-decoder.rst     | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/Documentation/userspace-api/media/v4l/dev-decoder.rst b/Documentation/userspace-api/media/v4l/dev-decoder.rst
index ef8e8cf31f90..51d6da3eea4a 100644
--- a/Documentation/userspace-api/media/v4l/dev-decoder.rst
+++ b/Documentation/userspace-api/media/v4l/dev-decoder.rst
@@ -784,8 +784,8 @@ before the sequence started. Last of the buffers will have the
 must check if there is any pending event and:
 
 * if a ``V4L2_EVENT_SOURCE_CHANGE`` event with ``changes`` set to
-  ``V4L2_EVENT_SRC_CH_RESOLUTION`` is pending, the `Dynamic Resolution
-  Change` sequence needs to be followed,
+  ``V4L2_EVENT_SRC_CH_RESOLUTION`` or ``V4L2_EVENT_SRC_CH_COLORSPACE`` is pending,
+  the `Dynamic Resolution Change` sequence needs to be followed,
 
 * if a ``V4L2_EVENT_EOS`` event is pending, the `End of Stream` sequence needs
   to be followed.
@@ -932,13 +932,17 @@ reflected by corresponding queries):
 
 * the minimum number of buffers needed for decoding,
 
-* bit-depth of the bitstream has been changed.
+* bit-depth of the bitstream has been changed,
+
+* colorspace of the bitstream has been changed.
 
 Whenever that happens, the decoder must proceed as follows:
 
 1.  After encountering a resolution change in the stream, the decoder sends a
     ``V4L2_EVENT_SOURCE_CHANGE`` event with ``changes`` set to
-    ``V4L2_EVENT_SRC_CH_RESOLUTION``.
+    ``V4L2_EVENT_SRC_CH_RESOLUTION``, or a colorspace change in the stream, the
+    decoder sends a ``V4L2_EVENT_SOURCE_CHANGE`` event with ``changes`` set to
+    ``V4L2_EVENT_SRC_CH_COLORSPACE``.
 
     .. important::
 
@@ -946,6 +950,11 @@ Whenever that happens, the decoder must proceed as follows:
        values applying to the stream after the resolution change, including
        queue formats, selection rectangles and controls.
 
+.. note::
+        A ``V4L2_EVENT_SOURCE_CHANGE`` event with ``changes`` set to
+        ``V4L2_EVENT_SRC_CH_RESOLUTION`` will affect the allocation, but
+        ``V4L2_EVENT_SRC_CH_COLORSPACE`` won't.
+
 2.  The decoder will then process and decode all remaining buffers from before
     the resolution change point.
 
-- 
2.43.0-rc1