linux-kernel - Re: [PATCH v2] drm/msm: Grab the GPU runtime in a6xx routines, not the GMU one

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Message-ID: <a4abf2dd-7bb9-2638-9684-8c140a22491e@quicinc.com>
Date:   Thu, 9 Jun 2022 23:34:16 +0530
From:   Akhil P Oommen <quic_akhilpo@...cinc.com>
To:     Douglas Anderson <dianders@...omium.org>,
        Rob Clark <robdclark@...il.com>,
        Jordan Crouse <jordan@...micpenguin.net>
CC:     Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Chia-I Wu <olvaffe@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        "Eric Anholt" <eric@...olt.net>,
        Jonathan Marek <jonathan@...ek.ca>,
        Sean Paul <sean@...rly.run>, Wang Qing <wangqing@...o.com>,
        Yangtao Li <tiny.windzz@...il.com>,
        <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] drm/msm: Grab the GPU runtime in a6xx routines, not
 the GMU one

On 6/9/2022 10:17 PM, Douglas Anderson wrote:
> >From testing on sc7180-trogdor devices, reading the GMU registers
> needs the GMU clocks to be enabled. Those clocks get turned on in
> a6xx_gmu_resume(). Confusingly enough, that function is called as a
> result of the runtime_pm of the GPU "struct device", not the GMU
> "struct device".
>
> Let's grab a reference to the correct device. Incidentally, this makes
> us match the a5xx routine more closely.
>
> This is easily shown to fix crashes that happen if we change the GPU's
> pm_runtime usage to not use autosuspend. It's also believed to fix
> some long tail GPU crashes even with autosuspend.
>
> NOTE: the crashes I've seen were fixed by _only_ fixing
> a6xx_gpu_busy(). However, I believe that the same arguments should be
> made to a6xx_gmu_set_freq() so I've fixed that case too. To make that
> fix clean, we've moved the pm runtime grabbing into the GPU file.
>
> As a bonus fix with this change, we change the pm_runtime get
> functions to check for <= 0 instead of ==. This handles the case where
> pm_runtime is disabled.
>
> Fixes: eadf79286a4b ("drm/msm: Check for powered down HW in the devfreq callbacks")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
> Changes in v2:
> - Move the set_freq runtime pm grab to the GPU file.
> - Use <= for the pm_runtime test, not ==.
>
>   drivers/gpu/drm/msm/adreno/a6xx_gmu.c |  9 ---------
>   drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 13 +++++++++++--
>   2 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> index 9f76f5b15759..2410815e77b4 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> @@ -125,17 +125,9 @@ void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp)
>   
>   	trace_msm_gmu_freq_change(gmu->freq, perf_index);
>   
> -	/*
> -	 * This can get called from devfreq while the hardware is idle. Don't
> -	 * bring up the power if it isn't already active
> -	 */
> -	if (pm_runtime_get_if_in_use(gmu->dev) == 0)
> -		return;
> -
>   	if (!gmu->legacy) {
>   		a6xx_hfi_set_freq(gmu, perf_index);
>   		dev_pm_opp_set_opp(&gpu->pdev->dev, opp);
> -		pm_runtime_put(gmu->dev);
>   		return;
>   	}
>   
> @@ -159,7 +151,6 @@ void a6xx_gmu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp)
>   		dev_err(gmu->dev, "GMU set GPU frequency error: %d\n", ret);
>   
>   	dev_pm_opp_set_opp(&gpu->pdev->dev, opp);
> -	pm_runtime_put(gmu->dev);
>   }
>   
>   unsigned long a6xx_gmu_get_freq(struct msm_gpu *gpu)
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index 42ed9a3c4905..54efd9b76ea6 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -1659,7 +1659,7 @@ static u64 a6xx_gpu_busy(struct msm_gpu *gpu, unsigned long *out_sample_rate)
>   	*out_sample_rate = 19200000;
>   
>   	/* Only read the gpu busy if the hardware is already active */
> -	if (pm_runtime_get_if_in_use(a6xx_gpu->gmu.dev) == 0)
> +	if (pm_runtime_get_if_in_use(&gpu->pdev->dev) <= 0)
You are changing the behavior here when CONFIG_PM is not enabled.

-Akhil.
>   		return 0;
>   
>   	busy_cycles = gmu_read64(&a6xx_gpu->gmu,
> @@ -1667,7 +1667,7 @@ static u64 a6xx_gpu_busy(struct msm_gpu *gpu, unsigned long *out_sample_rate)
>   			REG_A6XX_GMU_CX_GMU_POWER_COUNTER_XOCLK_0_H);
>   
>   
> -	pm_runtime_put(a6xx_gpu->gmu.dev);
> +	pm_runtime_put(&gpu->pdev->dev);
>   
>   	return busy_cycles;
>   }
> @@ -1677,9 +1677,18 @@ static void a6xx_gpu_set_freq(struct msm_gpu *gpu, struct dev_pm_opp *opp)
>   	struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
>   	struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
>   
> +	/*
> +	 * This can get called from devfreq while the hardware is idle. Don't
> +	 * bring up the power if it isn't already active
> +	 */
> +	if (pm_runtime_get_if_in_use(&gpu->pdev->dev) <= 0)
> +		return;
> +
>   	mutex_lock(&a6xx_gpu->gmu.lock);
>   	a6xx_gmu_set_freq(gpu, opp);
>   	mutex_unlock(&a6xx_gpu->gmu.lock);
> +
> +	pm_runtime_put(&gpu->pdev->dev);
>   }
>   
>   static struct msm_gem_address_space *