Messages in this thread | | | Date | Thu, 21 Jul 2022 02:08:32 +0530 | Subject | Re: [Freedreno] [PATCH v2 3/7] drm/msm: Fix cx collapse issue during recovery | From | Akhil P Oommen <> |
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On 7/20/2022 11:36 PM, Rob Clark wrote: > On Tue, Jul 12, 2022 at 12:15 PM Akhil P Oommen > <quic_akhilpo@quicinc.com> wrote: >> On 7/12/2022 10:14 PM, Rob Clark wrote: >>> On Mon, Jul 11, 2022 at 10:05 PM Akhil P Oommen >>> <quic_akhilpo@quicinc.com> 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@quicinc.com> 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@quicinc.com> >>>>>> --- >>>>>> >>>>>> (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? >> > But I think without #1 you could still be racing w/ some other path > that touches the hw, like devfreq, right. They could be holding a > runpm ref, so even if you loop over active_submits decrementing the > runpm ref, it still doesn't drop to zero > > BR, > -R Yes, you are right. There could be some transient votes from other threads/drivers/subsystem. This is the reason we need to poll for cx gdsc collapse in the next patch.Even with #1, it is difficult to coordinate with smmu driver and close to impossible with tz/hyp.
-Akhil.
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