Re: [PATCH v3 9/9] media: subdev: Support single-stream case in v4l2_subdev_enable/disable_streams()

From: Tomi Valkeinen
Date: Thu Apr 11 2024 - 07:07:51 EST


On 11/04/2024 14:02, Umang Jain wrote:
Hi Tomi,

On 10/04/24 6:05 pm, Tomi Valkeinen wrote:
At the moment the v4l2_subdev_enable/disable_streams() functions call
fallback helpers to handle the case where the subdev only implements
.s_stream(), and the main function handles the case where the subdev
implements streams (V4L2_SUBDEV_FL_STREAMS, which implies
.enable/disable_streams()).

What is missing is support for subdevs which do not implement streams
support, but do implement .enable/disable_streams(). Example cases of
these subdevices are single-stream cameras, where using
.enable/disable_streams() is not required but helps us remove the users
of the legacy .s_stream(), and subdevices with multiple source pads (but
single stream per pad), where .enable/disable_streams() allows the
subdevice to control the enable/disable state per pad.

The two single-streams cases (.s_stream() and .enable/disable_streams())
are very similar, and with small changes we can change the
v4l2_subdev_enable/disable_streams() functions to support all three
cases, without needing separate fallback functions.

A few potentially problematic details, though:

Does this mean the patch needs to be worked upon more ?

I don't see the two issues below as blockers.

I quickly tested the series by applying it locally with my use case of IMX283 .enable/disable streams and s_stream as the helper function and it seems I am still seeing the same behaviour as before (i.e. not being streamed) and have to carry the workaround as mentioned in [1] **NOTE**

Ok... Then something bugs here, as it is supposed to fix the problem. Can you trace the code a bit to see where it goes wrong?

The execution should go to the "if (!(sd->flags & V4L2_SUBDEV_FL_STREAMS))" blocks in v4l2_subdev_collect_streams() and v4l2_subdev_set_streams_enabled(),

Tomi


[1] https://lore.kernel.org/linux-media/20240313070705.91140-1-umang.jain@xxxxxxxxxxxxxxxx/


- For the single-streams cases we use sd->enabled_pads field, which
   limits the number of pads for the subdevice to 64. For simplicity I
   added the check for this limitation to the beginning of the function,
   and it also applies to the streams case.

- The fallback functions only allowed the target pad to be a source pad.
   It is not very clear to me why this check was needed, but it was not
   needed in the streams case. However, I doubt the
   v4l2_subdev_enable/disable_streams() code has ever been tested with
   sink pads, so to be on the safe side, I added the same check
   to the v4l2_subdev_enable/disable_streams() functions.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
---
  drivers/media/v4l2-core/v4l2-subdev.c | 187 ++++++++++++++--------------------
  1 file changed, 79 insertions(+), 108 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
index 0d376d72ecc7..4a73886741f9 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -2106,6 +2106,13 @@ static void v4l2_subdev_collect_streams(struct v4l2_subdev *sd,
                      u64 *found_streams,
                      u64 *enabled_streams)
  {
+    if (!(sd->flags & V4L2_SUBDEV_FL_STREAMS)) {
+        *found_streams = BIT_ULL(0);
+        if (sd->enabled_pads & BIT_ULL(pad))
+            *enabled_streams = BIT_ULL(0);
+        return;
+    }
+
      *found_streams = 0;
      *enabled_streams = 0;
@@ -2127,6 +2134,14 @@ static void v4l2_subdev_set_streams_enabled(struct v4l2_subdev *sd,
                          u32 pad, u64 streams_mask,
                          bool enabled)
  {
+    if (!(sd->flags & V4L2_SUBDEV_FL_STREAMS)) {
+        if (enabled)
+            sd->enabled_pads |= BIT_ULL(pad);
+        else
+            sd->enabled_pads &= ~BIT_ULL(pad);
+        return;
+    }
+
      for (unsigned int i = 0; i < state->stream_configs.num_configs; ++i) {
          struct v4l2_subdev_stream_config *cfg =
              &state->stream_configs.configs[i];
@@ -2136,51 +2151,6 @@ static void v4l2_subdev_set_streams_enabled(struct v4l2_subdev *sd,
      }
  }
-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;
-    int ret;
-
-    /*
-     * The subdev doesn't implement pad-based stream enable, fall back
-     * to the .s_stream() operation.
-     */
-    if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
-        return -EOPNOTSUPP;
-
-    /*
-     * .s_stream() means there is no streams support, so only allowed stream
-     * is the implicit 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) * BITS_PER_BYTE)
-        return -EOPNOTSUPP;
-
-    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 pad is enabled. */
-    if (!sd->enabled_pads) {
-        ret = v4l2_subdev_call(sd, video, s_stream, 1);
-        if (ret)
-            return ret;
-    }
-
-    sd->enabled_pads |= BIT_ULL(pad);
-
-    return 0;
-}
-
  int v4l2_subdev_enable_streams(struct v4l2_subdev *sd, u32 pad,
                     u64 streams_mask)
  {
@@ -2189,21 +2159,33 @@ int v4l2_subdev_enable_streams(struct v4l2_subdev *sd, u32 pad,
      bool already_streaming;
      u64 enabled_streams;
      u64 found_streams;
+    bool use_s_stream;
      int ret;
      /* A few basic sanity checks first. */
      if (pad >= sd->entity.num_pads)
          return -EINVAL;
+    if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
+        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) * BITS_PER_BYTE)
+        return -EOPNOTSUPP;
+
      if (!streams_mask)
          return 0;
      /* Fallback on .s_stream() if .enable_streams() isn't available. */
-    if (!v4l2_subdev_has_op(sd, pad, enable_streams))
-        return v4l2_subdev_enable_streams_fallback(sd, pad,
-                               streams_mask);
+    use_s_stream = !v4l2_subdev_has_op(sd, pad, enable_streams);
-    state = v4l2_subdev_lock_and_get_active_state(sd);
+    if (!use_s_stream)
+        state = v4l2_subdev_lock_and_get_active_state(sd);
+    else
+        state = NULL;
      /*
       * Verify that the requested streams exist and that they are not
@@ -2231,9 +2213,18 @@ int v4l2_subdev_enable_streams(struct v4l2_subdev *sd, u32 pad,
      already_streaming = v4l2_subdev_is_streaming(sd);
-    /* Call the .enable_streams() operation. */
-    ret = v4l2_subdev_call(sd, pad, enable_streams, state, pad,
-                   streams_mask);
+    if (!use_s_stream) {
+        /* Call the .enable_streams() operation. */
+        ret = v4l2_subdev_call(sd, pad, enable_streams, state, pad,
+                       streams_mask);
+    } else {
+        /* Start streaming when the first pad is enabled. */
+        if (!already_streaming)
+            ret = v4l2_subdev_call(sd, video, s_stream, 1);
+        else
+            ret = 0;
+    }
+
      if (ret) {
          dev_dbg(dev, "enable streams %u:%#llx failed: %d\n", pad,
              streams_mask, ret);
@@ -2243,34 +2234,32 @@ int v4l2_subdev_enable_streams(struct v4l2_subdev *sd, u32 pad,
      /* Mark the streams as enabled. */
      v4l2_subdev_set_streams_enabled(sd, state, pad, streams_mask, true);
-    if (!already_streaming)
+    if (!use_s_stream && !already_streaming)
          v4l2_subdev_enable_privacy_led(sd);
  done:
-    v4l2_subdev_unlock_state(state);
+    if (!use_s_stream)
+        v4l2_subdev_unlock_state(state);
      return ret;
  }
  EXPORT_SYMBOL_GPL(v4l2_subdev_enable_streams);
-static int v4l2_subdev_disable_streams_fallback(struct v4l2_subdev *sd, u32 pad,
-                        u64 streams_mask)
+int v4l2_subdev_disable_streams(struct v4l2_subdev *sd, u32 pad,
+                u64 streams_mask)
  {
      struct device *dev = sd->entity.graph_obj.mdev->dev;
+    struct v4l2_subdev_state *state;
+    u64 enabled_streams;
+    u64 found_streams;
+    bool use_s_stream;
      int ret;
-    /*
-     * If the subdev doesn't implement pad-based stream enable, fall back
-     * to the .s_stream() operation.
-     */
-    if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
-        return -EOPNOTSUPP;
+    /* A few basic sanity checks first. */
+    if (pad >= sd->entity.num_pads)
+        return -EINVAL;
-    /*
-     * .s_stream() means there is no streams support, so only allowed stream
-     * is the implicit stream 0.
-     */
-    if (streams_mask != BIT_ULL(0))
+    if (!(sd->entity.pads[pad].flags & MEDIA_PAD_FL_SOURCE))
          return -EOPNOTSUPP;
      /*
@@ -2280,46 +2269,16 @@ static int v4l2_subdev_disable_streams_fallback(struct v4l2_subdev *sd, u32 pad,
      if (pad >= sizeof(sd->enabled_pads) * BITS_PER_BYTE)
          return -EOPNOTSUPP;
-    if (!(sd->enabled_pads & 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_pads & ~BIT_ULL(pad))) {
-        ret = v4l2_subdev_call(sd, video, s_stream, 0);
-        if (ret)
-            return ret;
-    }
-
-    sd->enabled_pads &= ~BIT_ULL(pad);
-
-    return 0;
-}
-
-int v4l2_subdev_disable_streams(struct v4l2_subdev *sd, u32 pad,
-                u64 streams_mask)
-{
-    struct device *dev = sd->entity.graph_obj.mdev->dev;
-    struct v4l2_subdev_state *state;
-    u64 enabled_streams;
-    u64 found_streams;
-    int ret;
-
-    /* A few basic sanity checks first. */
-    if (pad >= sd->entity.num_pads)
-        return -EINVAL;
-
      if (!streams_mask)
          return 0;
      /* Fallback on .s_stream() if .disable_streams() isn't available. */
-    if (!v4l2_subdev_has_op(sd, pad, disable_streams))
-        return v4l2_subdev_disable_streams_fallback(sd, pad,
-                                streams_mask);
+    use_s_stream = !v4l2_subdev_has_op(sd, pad, disable_streams);
-    state = v4l2_subdev_lock_and_get_active_state(sd);
+    if (!use_s_stream)
+        state = v4l2_subdev_lock_and_get_active_state(sd);
+    else
+        state = NULL;
      /*
       * Verify that the requested streams exist and that they are not
@@ -2345,9 +2304,19 @@ int v4l2_subdev_disable_streams(struct v4l2_subdev *sd, u32 pad,
      dev_dbg(dev, "disable streams %u:%#llx\n", pad, streams_mask);
-    /* Call the .disable_streams() operation. */
-    ret = v4l2_subdev_call(sd, pad, disable_streams, state, pad,
-                   streams_mask);
+    if (!use_s_stream) {
+        /* Call the .disable_streams() operation. */
+        ret = v4l2_subdev_call(sd, pad, disable_streams, state, pad,
+                       streams_mask);
+    } else {
+        /* Stop streaming when the last streams are disabled. */
+
+        if (!(sd->enabled_pads & ~BIT_ULL(pad)))
+            ret = v4l2_subdev_call(sd, video, s_stream, 0);
+        else
+            ret = 0;
+    }
+
      if (ret) {
          dev_dbg(dev, "disable streams %u:%#llx failed: %d\n", pad,
              streams_mask, ret);
@@ -2357,10 +2326,12 @@ int v4l2_subdev_disable_streams(struct v4l2_subdev *sd, u32 pad,
      v4l2_subdev_set_streams_enabled(sd, state, pad, streams_mask, false);
  done:
-    if (!v4l2_subdev_is_streaming(sd))
-        v4l2_subdev_disable_privacy_led(sd);
+    if (!use_s_stream) {
+        if (!v4l2_subdev_is_streaming(sd))
+            v4l2_subdev_disable_privacy_led(sd);
-    v4l2_subdev_unlock_state(state);
+        v4l2_subdev_unlock_state(state);
+    }
      return ret;
  }