Re: [PATCH v2 4/9] media: subdev: Fix use of sd->enabled_streams in call_s_stream()

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On 10/04/2024 13:05, Sakari Ailus wrote:

On Fri, Apr 05, 2024 at 12:14:22PM +0300, Tomi Valkeinen wrote:
call_s_stream() uses sd->enabled_streams to track whether streaming has
already been enabled. However,
v4l2_subdev_enable/disable_streams_fallback(), which was the original
user of this field, already uses it, and
v4l2_subdev_enable/disable_streams_fallback() will call call_s_stream().

This leads to a conflict as both functions set the field. Afaics, both
functions set the field to the same value, so it won't cause a runtime
bug, but it's still wrong and if we, e.g., change how
v4l2_subdev_enable/disable_streams_fallback() operates we might easily
cause bugs.

Fix this by adding a new field, 'streaming_enabled', for

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
  drivers/media/v4l2-core/v4l2-subdev.c | 8 ++------
  include/media/v4l2-subdev.h           | 3 +++
  2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
index a15a41576918..94483b238f2a 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -421,12 +421,8 @@ static int call_s_stream(struct v4l2_subdev *sd, int enable)
  	 * The .s_stream() operation must never be called to start or stop an
  	 * already started or stopped subdev. Catch offenders but don't return
  	 * an error yet to avoid regressions.
-	 *
-	 * As .s_stream() is mutually exclusive with the .enable_streams() and
-	 * .disable_streams() operation, we can use the enabled_streams field
-	 * to store the subdev streaming state.
-	if (WARN_ON(!!sd->enabled_streams == !!enable))
+	if (WARN_ON(!!sd->streaming_enabled == !!enable))

A single ! is enough on both sides.

Or perhaps (sd->streaming_enabled == !!enable).

  		return 0;
if (enable)
@@ -442,7 +438,7 @@ static int call_s_stream(struct v4l2_subdev *sd, int enable)
if (!ret)
-		sd->enabled_streams = enable ? BIT(0) : 0;
+		sd->streaming_enabled = !!enable;

No need for !! unless you think it needs to be very loud. Casting a
non-boolean value to boolean results in true if it's non-zero.

Indeed. My coding style for booleans seems to be from times long past.


return ret;
diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
index a9e6b8146279..f55d03e0acc1 100644
--- a/include/media/v4l2-subdev.h
+++ b/include/media/v4l2-subdev.h
@@ -1043,6 +1043,8 @@ struct v4l2_subdev_platform_data {
   *		     v4l2_subdev_enable_streams() and
   *		     v4l2_subdev_disable_streams() helper functions for fallback
   *		     cases.
+ * @streaming_enabled: Tracks whether streaming has been enabled with s_stream.
+ *                     This is only for call_s_stream() internal use.
   * Each instance of a subdev driver should create this struct, either
   * stand-alone or embedded in a larger struct.
@@ -1091,6 +1093,7 @@ struct v4l2_subdev {
  	struct v4l2_subdev_state *active_state;
  	u64 enabled_streams;
+	bool streaming_enabled;

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