Re: [PATCH v3 4/9] media: subdev: Fix use of sd->enabled_streams in call_s_stream()

From: Tomi Valkeinen
Date: Thu Apr 11 2024 - 02:19:19 EST


On 11/04/2024 08:16, Umang Jain wrote:
Hi Tomi,

Thank you for the patch

On 10/04/24 6:05 pm, 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
call_s_stream().

Just a suggestion, as this is only used in call_s_stream(), maybe naming this field 's_stream_enabled' ?

Yes, I think that's a good idea.

Tomi

Rest looks good to me,

Reviewed-by: Umang Jain <umang.jain@xxxxxxxxxxxxxxxx>


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 606a909cd778..6cd353d83dfc 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))
          return 0;
      ret = sd->ops->video->s_stream(sd, enable);
@@ -437,7 +433,7 @@ static int call_s_stream(struct v4l2_subdev *sd, int enable)
      }
      if (!ret) {
-        sd->enabled_streams = enable ? BIT(0) : 0;
+        sd->streaming_enabled = enable;
          if (enable)
              v4l2_subdev_enable_privacy_led(sd);
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;
  };