linux-kernel - Re: [PATCH v2 06/14] drm/msm/gpu: Use dev_pm_opp_set

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Date:   Fri, 17 Feb 2023 23:07:05 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        linux-arm-msm@...r.kernel.org, andersson@...nel.org,
        agross@...nel.org
Cc:     marijn.suijten@...ainline.org, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>,
        Emma Anholt <emma@...olt.net>, Chia-I Wu <olvaffe@...il.com>,
        Dan Carpenter <error27@...il.com>,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/14] drm/msm/gpu: Use dev_pm_opp_set_rate for non-GMU
 GPUs

On 14/02/2023 19:31, Konrad Dybcio wrote:
> Currently we only utilize the OPP table connected to the GPU for
> getting (available) frequencies. We do however need to scale the
> voltage rail(s) accordingly to ensure that we aren't trying to
> run the GPU at 1GHz with a VDD_LOW vote, as that would result in
> an otherwise inexplainable hang.
> 
> Tell the OPP framework that we want to scale the "core" clock
> and swap out the clk_set_rate to a dev_pm_opp_set_rate in
> msm_devfreq_target() to enable usage of required-opps and by
> extension proper voltage level/corner scaling.
> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> ---
>   drivers/gpu/drm/msm/adreno/adreno_gpu.c | 4 ++++
>   drivers/gpu/drm/msm/msm_gpu_devfreq.c   | 2 +-
>   2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.c b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> index ce6b76c45b6f..15e405e4f977 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> @@ -1047,6 +1047,10 @@ int adreno_gpu_init(struct drm_device *drm, struct platform_device *pdev,
>   	const char *gpu_name;
>   	u32 speedbin;
>   
> +	/* This can only be done here, or devm_pm_opp_set_supported_hw will WARN_ON() */
> +	if (!IS_ERR(devm_clk_get(dev, "core")))
> +		devm_pm_opp_set_clkname(dev, "core");

Can we instead move a call to a6xx_set_supported_hw() / check_speed_bin 
after the adreno_gpu_init() ? It will call msm_gpu_init, which in turn 
sets gpu->core_clk.

Ideally you can call devm_pm_opp_set_clkname() from that function. Or 
maybe completely drop gpu->core_clk and always use 
devm_pm_opp_set_clk_rate().

> +
>   	adreno_gpu->funcs = funcs;
>   	adreno_gpu->info = adreno_info(config->rev);
>   	adreno_gpu->gmem = adreno_gpu->info->gmem;
> diff --git a/drivers/gpu/drm/msm/msm_gpu_devfreq.c b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> index e27dbf12b5e8..ea70c1c32d94 100644
> --- a/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> +++ b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> @@ -48,7 +48,7 @@ static int msm_devfreq_target(struct device *dev, unsigned long *freq,
>   		gpu->funcs->gpu_set_freq(gpu, opp, df->suspended);
>   		mutex_unlock(&df->lock);
>   	} else {
> -		clk_set_rate(gpu->core_clk, *freq);
> +		dev_pm_opp_set_rate(dev, *freq);

This is not enough, there are calls to clk_set_rate(gpu->core_clk) in 
msm_gpu.c which are called from the suspend/resume path.

>   	}
>   
>   	dev_pm_opp_put(opp);

-- 
With best wishes
Dmitry