linux-kernel - Re: [PATCH v3 1/8] drm/msm: Remove unnecessary pm_runtime

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Date:   Mon, 1 Aug 2022 20:02:41 +0530
From:   Akhil P Oommen <quic_akhilpo@...cinc.com>
To:     Rob Clark <robdclark@...il.com>
CC:     freedreno <freedreno@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        "Bjorn Andersson" <bjorn.andersson@...aro.org>,
        Jordan Crouse <jordan@...micpenguin.net>,
        Jonathan Marek <jonathan@...ek.ca>,
        "Douglas Anderson" <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/8] drm/msm: Remove unnecessary pm_runtime_get/put

On 7/31/2022 9:25 PM, Rob Clark wrote:
> On Sat, Jul 30, 2022 at 2:41 AM Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
>> We already enable gpu power from msm_gpu_submit(), so avoid a duplicate
>> pm_runtime_get/put from msm_job_run().
>>
>> Signed-off-by: Akhil P Oommen <quic_akhilpo@...cinc.com>
>> ---
>>
>> (no changes since v1)
>>
>>   drivers/gpu/drm/msm/msm_ringbuffer.c | 4 ----
>>   1 file changed, 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/msm_ringbuffer.c b/drivers/gpu/drm/msm/msm_ringbuffer.c
>> index 56eecb4..cad4c35 100644
>> --- a/drivers/gpu/drm/msm/msm_ringbuffer.c
>> +++ b/drivers/gpu/drm/msm/msm_ringbuffer.c
>> @@ -29,8 +29,6 @@ static struct dma_fence *msm_job_run(struct drm_sched_job *job)
>>                  msm_gem_unlock(obj);
>>          }
>>
>> -       pm_runtime_get_sync(&gpu->pdev->dev);
>> -
> This is removing a _get_sync() and simply relying on a _get() (async)
> in msm_gpu_submit().. that seems pretty likely to go badly?  I think
> it should probably replace the _get() in msm_gpu_submit() with
> _get_sync() (but also since this is changing position of
> resume/suspend vs active_lock, please make sure you test with lockdep
> enabled)
>
> BR,
> -R
As discussed in the other patch, this is correctly handled in 
msm_gpu_submit(). And from active_lock perspective, there is no change 
actually. GPU is ON by the time we touch active_lock in both cases.

-Akhil.
>>          /* TODO move submit path over to using a per-ring lock.. */
>>          mutex_lock(&gpu->lock);
>>
>> @@ -38,8 +36,6 @@ static struct dma_fence *msm_job_run(struct drm_sched_job *job)
>>
>>          mutex_unlock(&gpu->lock);
>>
>> -       pm_runtime_put(&gpu->pdev->dev);
>> -
>>          return dma_fence_get(submit->hw_fence);
>>   }
>>
>> --
>> 2.7.4
>>