The single frame_sequence counter in struct mali_c55_isp is incremented in mali_c55_set_plane_done(), which runs once per completed buffer per capture device rather than once per frame. Hardware fitted with the downscale pipe always hits this: mali_c55_pipeline_ready() refuses to start the ISP unless both the full-resolution and the downscale queues are streaming, so the counter advances twice per frame. Each video node then reports sequence numbers 0, 2, 4, ..., which userspace reads as a dropped frame between every pair of frames, and the two pipes never number the same frame alike, contrary to Documentation/admin-guide/media/mali-c55.rst. The V4L2_EVENT_FRAME_SYNC event and the statistics and parameters buffers only read the counter, so their sequence numbers stop identifying a frame too. Increment the counter once per frame, when the ISP start interrupt is handled, and stamp each capture buffer when mali_c55_set_next_buffer() programs it, as it is written out during the following frame. Stamping at completion would be off by one whenever DONE(n) and START(n+1) are handled in the same interrupt, since ISP_START is processed first. Hold the counter at UINT_MAX while the ISP is stopped, as the first buffers are programmed before it starts, so the first frame gets sequence zero. Fixes: d5f281f3dd29 ("media: mali-c55: Add Mali-C55 ISP driver") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-5 Signed-off-by: David Carlier --- v2: - Stamp the buffer sequence in mali_c55_set_next_buffer() instead of at completion, which broke when START(n+1) and DONE(n) are handled together (Jacopo) - Reset the counter when the ISP stops instead of when it starts v1: https://lore.kernel.org/r/20260801205311.386692-1-devnexen@gmail.com --- drivers/media/platform/arm/mali-c55/mali-c55-capture.c | 5 +++-- drivers/media/platform/arm/mali-c55/mali-c55-common.h | 4 ++++ drivers/media/platform/arm/mali-c55/mali-c55-core.c | 1 + drivers/media/platform/arm/mali-c55/mali-c55-isp.c | 3 ++- 4 files changed, 10 insertions(+), 3 deletions(-) diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-capture.c b/drivers/media/platform/arm/mali-c55/mali-c55-capture.c index ff01553026fb..fa073ce4b2bd 100644 --- a/drivers/media/platform/arm/mali-c55/mali-c55-capture.c +++ b/drivers/media/platform/arm/mali-c55/mali-c55-capture.c @@ -413,6 +413,9 @@ void mali_c55_set_next_buffer(struct mali_c55_cap_dev *cap_dev) return; } + /* The buffer is written out during the frame following this one. */ + buf->vb.sequence = cap_dev->mali_c55->isp.frame_sequence + 1; + pix_mp = &cap_dev->format.format; mali_c55_cap_dev_update_bits(cap_dev, MALI_C55_REG_Y_WRITER_MODE, @@ -457,7 +460,6 @@ void mali_c55_set_next_buffer(struct mali_c55_cap_dev *cap_dev) void mali_c55_set_plane_done(struct mali_c55_cap_dev *cap_dev, enum mali_c55_planes plane) { - struct mali_c55_isp *isp = &cap_dev->mali_c55->isp; struct mali_c55_buffer *buf; scoped_guard(spinlock, &cap_dev->buffers.processing_lock) { @@ -476,7 +478,6 @@ void mali_c55_set_plane_done(struct mali_c55_cap_dev *cap_dev, /* If the other plane is also done... */ buf->vb.vb2_buf.timestamp = ktime_get_boottime_ns(); - buf->vb.sequence = isp->frame_sequence++; vb2_buffer_done(&buf->vb.vb2_buf, VB2_BUF_STATE_DONE); } diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-common.h b/drivers/media/platform/arm/mali-c55/mali-c55-common.h index 13a3e9dc4243..50f2b7a85f62 100644 --- a/drivers/media/platform/arm/mali-c55/mali-c55-common.h +++ b/drivers/media/platform/arm/mali-c55/mali-c55-common.h @@ -76,6 +76,10 @@ struct mali_c55_isp { struct media_pad *remote_src; /* Mutex to guard vb2 start/stop streaming */ struct mutex capture_lock; + /* + * Sequence of the frame being processed, incremented at SOF. Held at + * UINT_MAX while stopped so the first frame gets sequence 0. + */ unsigned int frame_sequence; }; diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-core.c b/drivers/media/platform/arm/mali-c55/mali-c55-core.c index fb81141d1653..be562156b295 100644 --- a/drivers/media/platform/arm/mali-c55/mali-c55-core.c +++ b/drivers/media/platform/arm/mali-c55/mali-c55-core.c @@ -573,6 +573,7 @@ static irqreturn_t mali_c55_isr(int irq, void *context) for_each_set_bit(i, &interrupt_status, MALI_C55_NUM_IRQ_BITS) { switch (i) { case MALI_C55_IRQ_ISP_START: + mali_c55->isp.frame_sequence++; mali_c55_isp_queue_event_sof(mali_c55); mali_c55_set_next_buffer(&mali_c55->cap_devs[MALI_C55_CAP_DEV_FR]); diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-isp.c b/drivers/media/platform/arm/mali-c55/mali-c55-isp.c index e128adf6ee37..dd3bce287a3d 100644 --- a/drivers/media/platform/arm/mali-c55/mali-c55-isp.c +++ b/drivers/media/platform/arm/mali-c55/mali-c55-isp.c @@ -342,7 +342,6 @@ static int mali_c55_isp_enable_streams(struct v4l2_subdev *sd, src_sd = media_entity_to_v4l2_subdev(isp->remote_src->entity); - isp->frame_sequence = 0; ret = mali_c55_isp_start(mali_c55, state); if (ret) { dev_err(mali_c55->dev, "Failed to start ISP\n"); @@ -380,6 +379,7 @@ static int mali_c55_isp_disable_streams(struct v4l2_subdev *sd, isp->remote_src = NULL; mali_c55_isp_stop(mali_c55); + isp->frame_sequence = UINT_MAX; return 0; } @@ -584,6 +584,7 @@ int mali_c55_register_isp(struct mali_c55 *mali_c55) int ret; isp->mali_c55 = mali_c55; + isp->frame_sequence = UINT_MAX; v4l2_subdev_init(sd, &mali_c55_isp_ops); sd->flags |= V4L2_SUBDEV_FL_HAS_DEVNODE | V4L2_SUBDEV_FL_HAS_EVENTS; base-commit: 95f76f51937fdfb0fc1e14cae606b1ef574a56f3 -- 2.55.0