Re: [PATCH v2] drm/msm: Switch ordering of runpm put vs devfreq_idle

[Akhil P Oommen <quic_akhilpo@quicinc.com>]

On 6/8/2022 9:43 PM, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
>
> I've seen a few crashes like:
>
>      CPU: 0 PID: 216 Comm: A618-worker Tainted: G        W         5.4.196 #7
>      Hardware name: Google Wormdingler rev1+ INX panel board (DT)
>      pstate: 20c00009 (nzCv daif +PAN +UAO)
>      pc : msm_readl+0x14/0x34
>      lr : a6xx_gpu_busy+0x40/0x80
>      sp : ffffffc011b93ad0
>      x29: ffffffc011b93ad0 x28: ffffffe77cba3000
>      x27: 0000000000000001 x26: ffffffe77bb4c4ac
>      x25: ffffffa2f227dfa0 x24: ffffffa2f22aab28
>      x23: 0000000000000000 x22: ffffffa2f22bf020
>      x21: ffffffa2f22bf000 x20: ffffffc011b93b10
>      x19: ffffffc011bd4110 x18: 000000000000000e
>      x17: 0000000000000004 x16: 000000000000000c
>      x15: 000001be3a969450 x14: 0000000000000400
>      x13: 00000000000101d6 x12: 0000000034155555
>      x11: 0000000000000001 x10: 0000000000000000
>      x9 : 0000000100000000 x8 : ffffffc011bd4000
>      x7 : 0000000000000000 x6 : 0000000000000007
>      x5 : ffffffc01d8b38f0 x4 : 0000000000000000
>      x3 : 00000000ffffffff x2 : 0000000000000002
>      x1 : 0000000000000000 x0 : ffffffc011bd4110
>      Call trace:
>       msm_readl+0x14/0x34
>       a6xx_gpu_busy+0x40/0x80
>       msm_devfreq_get_dev_status+0x70/0x1d0
>       devfreq_simple_ondemand_func+0x34/0x100
>       update_devfreq+0x50/0xe8
>       qos_notifier_call+0x2c/0x64
>       qos_max_notifier_call+0x1c/0x2c
>       notifier_call_chain+0x58/0x98
>       __blocking_notifier_call_chain+0x74/0x84
>       blocking_notifier_call_chain+0x38/0x48
>       pm_qos_update_target+0xf8/0x19c
>       freq_qos_apply+0x54/0x6c
>       apply_constraint+0x60/0x104
>       __dev_pm_qos_update_request+0xb4/0x184
>       dev_pm_qos_update_request+0x38/0x58
>       msm_devfreq_idle_work+0x34/0x40
>       kthread_worker_fn+0x144/0x1c8
>       kthread+0x140/0x284
>       ret_from_fork+0x10/0x18
>      Code: f9000bf3 910003fd aa0003f3 d503201f (b9400260)
>      ---[ end trace f6309767a42d0831 ]---
>
> Which smells a lot like touching hw after power collapse.  This seems
> a bit like a race/timing issue elsewhere, as pm_runtime_get_if_in_use()
> in a6xx_gpu_busy() should have kept us from touching hw if it wasn't
> powered.
>
> But, we've seen cases where the idle_work scheduled by
> msm_devfreq_idle() ends up racing with the resume path.  Which, again,
> shouldn't be a problem other than unnecessary freq changes.
>
> v2. Only move the runpm _put_autosuspend, and not the _mark_last_busy()
>
> Fixes: 9bc95570175a ("drm/msm: Devfreq tuning")
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> Link: https://lore.kernel.org/r/20210927152928.831245-1-robdclark@gmail.com
> ---
>   drivers/gpu/drm/msm/msm_gpu.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
> index eb8a6663f309..244511f85044 100644
> --- a/drivers/gpu/drm/msm/msm_gpu.c
> +++ b/drivers/gpu/drm/msm/msm_gpu.c
> @@ -672,7 +672,6 @@ static void retire_submit(struct msm_gpu *gpu, struct msm_ringbuffer *ring,
>   	msm_submit_retire(submit);
>   
>   	pm_runtime_mark_last_busy(&gpu->pdev->dev);
> -	pm_runtime_put_autosuspend(&gpu->pdev->dev);
>   
>   	spin_lock_irqsave(&ring->submit_lock, flags);
>   	list_del(&submit->node);
> @@ -686,6 +685,8 @@ static void retire_submit(struct msm_gpu *gpu, struct msm_ringbuffer *ring,
>   		msm_devfreq_idle(gpu);
>   	mutex_unlock(&gpu->active_lock);
>   
> +	pm_runtime_put_autosuspend(&gpu->pdev->dev);
> +
>   	msm_gem_submit_put(submit);
>   }
>   

Reviewed-by: Akhil P Oommen <quic_akhilpo@quicinc.com>


-Akhil.