Re: [PATCH v2] drm/msm/dpu: make "vblank timeout" more useful
From: Abhinav Kumar
Date: Tue Feb 20 2024 - 18:05:12 EST
On 2/20/2024 2:42 PM, Dmitry Baryshkov wrote:
On Wed, 21 Feb 2024 at 00:40, Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> wrote:
On 2/19/2024 3:52 AM, Dmitry Baryshkov wrote:
On Wed, 14 Feb 2024 at 22:36, Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> wrote:
On 2/14/2024 11:20 AM, Dmitry Baryshkov wrote:
On Wed, 14 Feb 2024 at 20:02, Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> wrote:
On 2/8/2024 6:50 AM, Dmitry Baryshkov wrote:
We have several reports of vblank timeout messages. However after some
debugging it was found that there might be different causes to that.
To allow us to identify the DPU block that gets stuck, include the
actual CTL_FLUSH value into the timeout message and trigger the devcore
snapshot capture.
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
---
Changes in v2:
- Added a call to msm_disp_snapshot_state() to trigger devcore dump
(Abhinav)
- Link to v1: https://lore.kernel.org/r/20240106-fd-dpu-debug-timeout-v1-1-6d9762884641@xxxxxxxxxx
---
drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
index d0f56c5c4cce..a8d6165b3c0a 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
@@ -489,7 +489,8 @@ static int dpu_encoder_phys_vid_wait_for_commit_done(
(hw_ctl->ops.get_flush_register(hw_ctl) == 0),
msecs_to_jiffies(50));
if (ret <= 0) {
- DPU_ERROR("vblank timeout\n");
+ DPU_ERROR("vblank timeout: %x\n", hw_ctl->ops.get_flush_register(hw_ctl));
+ msm_disp_snapshot_state(phys_enc->parent->dev);
There is no rate limiting in this piece of code unfortunately. So this
will flood the number of snapshots.
Well... Yes and no. The devcoredump will destroy other snapshots if
there is a pending one. So only the console will be flooded and only
in case when MSM_DISP_SNAPSHOT_DUMP_IN_CONSOLE is enabled.
Yes, true but at the same time this makes it hard to capture a good dump
as potentially every vblank you could timeout so this destroy/create
cycle wont end.
Excuse me, maybe I miss something. On the first timeout the snapshot
is created. It is held by the kernel until it is fully read out from
the userspace. Other snapshots will not interfere with this snapshot.
For every new snapshot a new devcoredump device will be created which
should remain till it has been read. But now this will be created every
blank. IMO, this is really too much data for no reason.
No-no-no. If there is a devcoredump for a device, the next one will
not be created. See dev_coredumpm().
So all the snapshots will be created and then destroyed immediately.
hmm ... I have certainly seen devcd_count go higher than one (but not
more than 2). I am wondering whether this was because of some race
condition of the previous destroy / new create.
But anyway, this part is clear now. thanks.
Subsequent vblank timeouts are not going to give any new information
compared to the existing snapshot of the first vblank timeout thats why
we should just create the snapshot when the first error happens and stop.
For other frame done timeouts, infact subsequent timeouts without any
sort of recovery in between are quite misleading because hardware was
already not able to fetch the previous frame so it will most likely not
fetch the next one either till it has recovered. Typically thats why
these vblank timeouts happen in a flurry as the hardware never really
recovered from the first timeout.
Or are you worried that snapshotting takes time, so taking a snapshot
will also interfere with the vblank timings for the next vblank?
Yes this is another point.
snapshots will still be captured every vblank timeout and reading
through the entire DPU reg space every vblank timeout is certainly
something we can avoid.