[FFmpeg-devel] [EXT] [PATCH 2/2] avcodec/v4l2_context: Log warning when all capture buffers are in userspace

[Ming Qian]

Lgtm,

But if don't prevent enqueue frame buffer of capture port, unlikely to happen this case.
And I think we can get a proper num_frame_buffers by g_ctrl V4L2_CID_MIN_BUFFERS_FOR_CAPTURE and V4L2_CID_MIN_BUFFERS_FOR_OUTPUT.



Best regards,
Ming Qian
Tel#:86-512-6805-6630


-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Andriy Gelman
Sent: Monday, April 6, 2020 12:22 PM
To: ffmpeg-devel at ffmpeg.org
Cc: Andriy Gelman <andriy.gelman at gmail.com>
Subject: [EXT] [FFmpeg-devel] [PATCH 2/2] avcodec/v4l2_context: Log warning when all capture buffers are in userspace

Caution: EXT Email

From: Andriy Gelman <andriy.gelman at gmail.com>

v4l2_m2m uses device memory mapped buffers to store dequeued frames/packets (reference counted by AVBufferRef). When the reference count drops to zero, the buffer ownership is returned back to the device, so that they can re-filled with frames/packets.

There are some cases when all the buffers are in userspace (i.e. due to internal buffering in ffmpeg). On the s5p-mfc this causes an infinite wait when polling to dequeue the buffers, which can be prevented by increasing the total number of capture buffers. This commit adds a warning when this occurs.

Signed-off-by: Andriy Gelman <andriy.gelman at gmail.com>
---
 libavcodec/v4l2_context.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/libavcodec/v4l2_context.c b/libavcodec/v4l2_context.c index 31af10d28e..5145772c45 100644
--- a/libavcodec/v4l2_context.c
+++ b/libavcodec/v4l2_context.c
@@ -285,6 +285,18 @@ static V4L2Buffer* v4l2_dequeue_v4l2buf(V4L2Context *ctx, int timeout)
     };
     int i, ret;

+    if (!V4L2_TYPE_IS_OUTPUT(ctx->type) && ctx->buffers) {
+        for (i = 0; i < ctx->num_buffers; i++) {
+            if (ctx->buffers[i].status == V4L2BUF_IN_DRIVER)
+                break;
+        }
+        if (i == ctx->num_buffers)
+            av_log(logger(ctx), AV_LOG_WARNING, "All capture buffers returned to "
+                                                "userspace. Increase num_capture_buffers "
+                                                "to prevent device deadlock or dropped "
+                                                "packets/frames.\n");
+    }
+
     /* if we are draining and there are no more capture buffers queued in the driver we are done */
     if (!V4L2_TYPE_IS_OUTPUT(ctx->type) && ctx_to_m2mctx(ctx)->draining) {
         for (i = 0; i < ctx->num_buffers; i++) {
--
2.25.1

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