Re: [Freedreno] [PATCH v2 3/7] drm/msm: Fix cx collapse issue during recovery

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On 7/12/2022 10:14 PM, Rob Clark wrote:
On Mon, Jul 11, 2022 at 10:05 PM Akhil P Oommen
<quic_akhilpo@xxxxxxxxxxx> wrote:
On 7/12/2022 4:52 AM, Doug Anderson wrote:
Hi,

On Fri, Jul 8, 2022 at 11:00 PM Akhil P Oommen <quic_akhilpo@xxxxxxxxxxx> wrote:
There are some hardware logic under CX domain. For a successful
recovery, we should ensure cx headswitch collapses to ensure all the
stale states are cleard out. This is especially true to for a6xx family
where we can GMU co-processor.

Currently, cx doesn't collapse due to a devlink between gpu and its
smmu. So the *struct gpu device* needs to be runtime suspended to ensure
that the iommu driver removes its vote on cx gdsc.

Signed-off-by: Akhil P Oommen <quic_akhilpo@xxxxxxxxxxx>
---

(no changes since v1)

   drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 16 ++++++++++++++--
   drivers/gpu/drm/msm/msm_gpu.c         |  2 --
   2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
index 4d50110..7ed347c 100644
--- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
+++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
@@ -1278,8 +1278,20 @@ static void a6xx_recover(struct msm_gpu *gpu)
           */
          gmu_write(&a6xx_gpu->gmu, REG_A6XX_GMU_GMU_PWR_COL_KEEPALIVE, 0);

-       gpu->funcs->pm_suspend(gpu);
-       gpu->funcs->pm_resume(gpu);
+       /*
+        * Now drop all the pm_runtime usage count to allow cx gdsc to collapse.
+        * First drop the usage count from all active submits
+        */
+       for (i = gpu->active_submits; i > 0; i--)
+               pm_runtime_put(&gpu->pdev->dev);
+
+       /* And the final one from recover worker */
+       pm_runtime_put_sync(&gpu->pdev->dev);
+
+       for (i = gpu->active_submits; i > 0; i--)
+               pm_runtime_get(&gpu->pdev->dev);
+
+       pm_runtime_get_sync(&gpu->pdev->dev);
In response to v1, Rob suggested pm_runtime_force_suspend/resume().
Those seem like they would work to me, too. Why not use them?
Quoting my previous response which I seem to have sent only to Freedreno
list:

"I believe it is supposed to be used only during system sleep state
transitions. Btw, we don't want pm_runtime_get() calls from elsewhere to
fail by disabling RPM here."
The comment about not wanting other runpm calls to fail is valid.. but
that is also solveable, ie. by holding a lock around runpm calls.
Which I think we need to do anyways, otherwise looping over
gpu->active_submits is racey..

I think pm_runtime_force_suspend/resume() is the least-bad option.. or
at least I'm not seeing any obvious alternative that is better

BR,
-R
We are holding gpu->lock here which will block further submissions from scheduler. Will active_submits still race?

It is possible that there is another thread which successfully completed pm_runtime_get() and while it access the hardware, we pulled the plug on regulator/clock here. That will result in obvious device crash. So I can think of 2 solutions:

1. wrap *every* pm_runtime_get/put with a mutex. Something like:
            mutex_lock();
            pm_runtime_get();
            < ... access hardware here >>
            pm_runtime_put();
            mutex_unlock();

2. Drop runtime votes from every submit in recover worker and wait/poll for regulator to collapse in case there are transient votes on regulator  from other threads/subsystems.

Option (2) seems simpler to me.  What do you think?

-Akhil.




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