linux-kernel - Re: [PATCH v2] drm/msm: Switch ordering of runpm put vs devfreq

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Date:   Thu, 9 Jun 2022 09:50:37 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>,
        Rob Clark <robdclark@...omium.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] drm/msm: Switch ordering of runpm put vs devfreq_idle

Hi,

On Wed, Jun 8, 2022 at 9:13 AM Rob Clark <robdclark@...il.com> wrote:
>
> From: Rob Clark <robdclark@...omium.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.

I dunno if we want to change the commit message since I think my patch
[1] addresses the above problem?

[1] https://lore.kernel.org/r/20220609094716.v2.1.Ie846c5352bc307ee4248d7cab998ab3016b85d06@changeid


> 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@...omium.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(-)

In any case, your patch fixes the potential WARN_ON and seems like the
right thing to do, so:

Reviewed-by: Douglas Anderson <dianders@...omium.org>