linux-kernel - Re: [Freedreno] [PATCH 3/3] drm/msm/gpu: Remove mutex from wait

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Message-ID: <3b066b63-c180-09c6-e39f-b408464b5bc1@quicinc.com>
Date:   Fri, 18 Mar 2022 02:15:34 +0530
From:   Akhil P Oommen <quic_akhilpo@...cinc.com>
To:     Rob Clark <robdclark@...il.com>, <dri-devel@...ts.freedesktop.org>
CC:     Rob Clark <robdclark@...omium.org>,
        Jonathan Marek <jonathan@...ek.ca>,
        David Airlie <airlied@...ux.ie>,
        <linux-arm-msm@...r.kernel.org>,
        "Vladimir Lypak" <vladimir.lypak@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Sean Paul <sean@...rly.run>, Daniel Vetter <daniel@...ll.ch>,
        <freedreno@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Subject: Re: [Freedreno] [PATCH 3/3] drm/msm/gpu: Remove mutex from wait_event
 condition

On 3/11/2022 5:16 AM, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
>
> The mutex wasn't really protecting anything before.  Before the previous
> patch we could still be racing with the scheduler's kthread, as that is
> not necessarily frozen yet.  Now that we've parked the sched threads,
> the only race is with jobs retiring, and that is harmless, ie.
>
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>   drivers/gpu/drm/msm/adreno/adreno_device.c | 11 +----------
>   1 file changed, 1 insertion(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_device.c b/drivers/gpu/drm/msm/adreno/adreno_device.c
> index 0440a98988fc..661dfa7681fb 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_device.c
> +++ b/drivers/gpu/drm/msm/adreno/adreno_device.c
> @@ -607,15 +607,6 @@ static int adreno_runtime_resume(struct device *dev)
>   	return gpu->funcs->pm_resume(gpu);
>   }
>   
> -static int active_submits(struct msm_gpu *gpu)
> -{
> -	int active_submits;
> -	mutex_lock(&gpu->active_lock);
> -	active_submits = gpu->active_submits;
> -	mutex_unlock(&gpu->active_lock);
I assumed that this lock here was to ensure proper barriers while 
reading active_submits. Is that not required?

-Akhil.
> -	return active_submits;
> -}
> -
>   static int adreno_runtime_suspend(struct device *dev)
>   {
>   	struct msm_gpu *gpu = dev_to_gpu(dev);
> @@ -669,7 +660,7 @@ static int adreno_system_suspend(struct device *dev)
>   	suspend_scheduler(gpu);
>   
>   	remaining = wait_event_timeout(gpu->retire_event,
> -				       active_submits(gpu) == 0,
> +				       gpu->active_submits == 0,
>   				       msecs_to_jiffies(1000));
>   	if (remaining == 0) {
>   		dev_err(dev, "Timeout waiting for GPU to suspend\n");