Re: [PATCH 3/4] media: subdev: Improve v4l2_subdev_enable/disable_streams_fallback

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On 04/04/2024 15:18, Sakari Ailus wrote:
Moi,

Thanks for the patch.

On Thu, Apr 04, 2024 at 01:50:02PM +0300, Tomi Valkeinen wrote:
v4l2_subdev_enable/disable_streams_fallback() supports falling back to
.s_stream() for subdevs with a single source pad. It also tracks the
enabled streams for that one pad in the sd->enabled_streams field.

Tracking the enabled streams with sd->enabled_streams does not make
sense, as with .s_stream() there can only be a single stream per pad.
Thus, as the v4l2_subdev_enable/disable_streams_fallback() only supports
a single source pad, all we really need is a boolean which tells whether
streaming has been enabled on this pad or not.

However, as we only need a true/false state for a pad (instead of
tracking which streams have been enabled for a pad), we can easily
extend the fallback mechanism to support multiple source pads as we only
need to keep track of which pads have been enabled.

Change the sd->enabled_streams field to sd->enabled_pads, which is a
64-bit bitmask tracking the enabled source pads. With this change we can
remove the restriction that
v4l2_subdev_enable/disable_streams_fallback() only supports a single
soruce pad.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
---
  drivers/media/v4l2-core/v4l2-subdev.c | 68 ++++++++++++++++++++---------------
  include/media/v4l2-subdev.h           |  9 +++--
  2 files changed, 44 insertions(+), 33 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
index 3b3310bce5d4..91298bb84e6b 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -2090,37 +2090,43 @@ static int v4l2_subdev_enable_streams_fallback(struct v4l2_subdev *sd, u32 pad,
  					       u64 streams_mask)
  {
  	struct device *dev = sd->entity.graph_obj.mdev->dev;
-	unsigned int i;
  	int ret;
/*
  	 * The subdev doesn't implement pad-based stream enable, fall back
-	 * on the .s_stream() operation. This can only be done for subdevs that
-	 * have a single source pad, as sd->enabled_streams is global to the
-	 * subdev.
+	 * on the .s_stream() operation.
  	 */
  	if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
  		return -EOPNOTSUPP;
- for (i = 0; i < sd->entity.num_pads; ++i) {
-		if (i != pad && sd->entity.pads[i].flags & MEDIA_PAD_FL_SOURCE)
-			return -EOPNOTSUPP;
-	}
+	/*
+	 * .s_stream() means there is no streams support, so only allowed stream
+	 * is the imlicit stream 0.
+	 */
+	if (streams_mask != BIT_ULL(0))
+		return -EOPNOTSUPP;
+
+	/*
+	 * We use a 64-bit bitmask for tracking enabled pads, so only subdevices
+	 * with 64 pads or less can be supported.
+	 */
+	if (pad >= sizeof(sd->enabled_pads) * 8)

s/8/BITS_PER_BYTE/

+		return -EOPNOTSUPP;
- if (sd->enabled_streams & streams_mask) {
-		dev_dbg(dev, "set of streams %#llx already enabled on %s:%u\n",
-			streams_mask, sd->entity.name, pad);
+	if (sd->enabled_pads & BIT_ULL(pad)) {
+		dev_dbg(dev, "pad %u already enabled on %s\n",
+			pad, sd->entity.name);
  		return -EALREADY;
  	}
- /* Start streaming when the first streams are enabled. */
-	if (!sd->enabled_streams) {
+	/* Start streaming when the first pad is enabled. */
+	if (!sd->enabled_pads) {
  		ret = v4l2_subdev_call(sd, video, s_stream, 1);
  		if (ret)
  			return ret;
  	}
- sd->enabled_streams |= streams_mask;
+	sd->enabled_pads |= BIT_ULL(pad);
return 0;
  }
@@ -2207,37 +2213,43 @@ static int v4l2_subdev_disable_streams_fallback(struct v4l2_subdev *sd, u32 pad,
  						u64 streams_mask)
  {
  	struct device *dev = sd->entity.graph_obj.mdev->dev;
-	unsigned int i;
  	int ret;
/*
-	 * If the subdev doesn't implement pad-based stream enable, fall  back
-	 * on the .s_stream() operation. This can only be done for subdevs that
-	 * have a single source pad, as sd->enabled_streams is global to the
-	 * subdev.
+	 * If the subdev doesn't implement pad-based stream enable, fall back
+	 * on the .s_stream() operation.
  	 */
  	if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
  		return -EOPNOTSUPP;
- for (i = 0; i < sd->entity.num_pads; ++i) {
-		if (i != pad && sd->entity.pads[i].flags & MEDIA_PAD_FL_SOURCE)
-			return -EOPNOTSUPP;
-	}
+	/*
+	 * .s_stream() means there is no streams support, so only allowed stream
+	 * is the imlicit stream 0.
+	 */
+	if (streams_mask != BIT_ULL(0))
+		return -EOPNOTSUPP;
+
+	/*
+	 * We use a 64-bit bitmask for tracking enabled pads, so only subdevices
+	 * with 64 pads or less can be supported.
+	 */
+	if (pad >= sizeof(sd->enabled_pads) * 8)

Ditto.

How much of the code of the two functions is the same? Could some of this
be put to a common function both would call? They look (almost) exactly the
same.

v4l2_subdev_enable_streams_fallback and v4l2_subdev_enable_streams? They have similar parts, but I don't right away see how combining them or making some common functions would help.

 Tomi


+		return -EOPNOTSUPP;
- if ((sd->enabled_streams & streams_mask) != streams_mask) {
-		dev_dbg(dev, "set of streams %#llx already disabled on %s:%u\n",
-			streams_mask, sd->entity.name, pad);
+	if ((sd->enabled_pads & BIT_ULL(pad)) != BIT_ULL(pad)) {
+		dev_dbg(dev, "pad %u already disabled on %s\n",
+			pad, sd->entity.name);
  		return -EALREADY;
  	}
/* Stop streaming when the last streams are disabled. */
-	if (!(sd->enabled_streams & ~streams_mask)) {
+	if (!(sd->enabled_pads & ~BIT_ULL(pad))) {
  		ret = v4l2_subdev_call(sd, video, s_stream, 0);
  		if (ret)
  			return ret;
  	}
- sd->enabled_streams &= ~streams_mask;
+	sd->enabled_pads &= ~BIT_ULL(pad);
return 0;
  }
diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
index 8bd1e3c96d2b..7077aec3176c 100644
--- a/include/media/v4l2-subdev.h
+++ b/include/media/v4l2-subdev.h
@@ -1039,10 +1039,9 @@ struct v4l2_subdev_platform_data {
   * @active_state: Active state for the subdev (NULL for subdevs tracking the
   *		  state internally). Initialized by calling
   *		  v4l2_subdev_init_finalize().
- * @enabled_streams: Bitmask of enabled streams used by
- *		     v4l2_subdev_enable_streams() and
- *		     v4l2_subdev_disable_streams() helper functions for fallback
- *		     cases.
+ * @enabled_pads: Bitmask of enabled pads used by 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.
   *
   * Each instance of a subdev driver should create this struct, either
@@ -1091,7 +1090,7 @@ struct v4l2_subdev {
  	 * doesn't support it.
  	 */
  	struct v4l2_subdev_state *active_state;
-	u64 enabled_streams;
+	u64 enabled_pads;
  	bool streaming_enabled;
  };






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