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Subject: Re: [PATCH] drm/msm: Disable frequency clamping on a630
To:     Rob Clark <robdclark@gmail.com>, dri-devel@lists.freedesktop.org
Cc:     freedreno@lists.freedesktop.org, linux-arm-msm@vger.kernel.org,
        Rob Clark <robdclark@chromium.org>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Jordan Crouse <jordan@cosmicpenguin.net>,
        Jonathan Marek <jonathan@marek.ca>,
        Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Sharat Masetty <smasetty@codeaurora.org>,
        Akhil P Oommen <akhilpo@codeaurora.org>,
        open list <linux-kernel@vger.kernel.org>
References: <20210729183942.2839925-1-robdclark@gmail.com>
From:   Caleb Connolly <caleb.connolly@linaro.org>
Message-ID: <1a38a590-a64e-58ef-1bbf-0ae49c004d05@linaro.org>
Date:   Thu, 29 Jul 2021 21:06:21 +0100
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Hi Rob,

I've done some more testing! It looks like before that patch ("drm/msm: Devfreq tuning") the GPU would never get above 
the second frequency in the OPP table (342MHz) (at least, not in glxgears). With the patch applied it would more 
aggressively jump up to the max frequency which seems to be unstable at the default regulator voltages.

Hacking the pm8005 s1 regulator (which provides VDD_GFX) up to 0.988v (instead of the stock 0.516v) makes the GPU stable 
at the higher frequencies.

Applying this patch reverts the behaviour, and the GPU never goes above 342MHz in glxgears, losing ~30% performance in 
glxgear.

I think (?) that enabling CPR support would be the proper solution to this - that would ensure that the regulators run 
at the voltage the hardware needs to be stable.

Is hacking the voltage higher (although ideally not quite that high) an acceptable short term solution until we have 
CPR? Or would it be safer to just not make use of the higher frequencies on a630 for now?


On 29/07/2021 19:39, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> The more frequent frequency transitions resulting from clamping freq to
> minimum when the GPU is idle seems to be causing some issue with the bus
> getting voted off when it should be on.  (An enable racing with an async
> disable?)  This might be a problem outside of the GPU, as I can't
> reproduce this on a618 which uses the same GMU fw and same mechanism to
> communicate with GMU to set opp.  For now, just revert to previous
> devfreq behavior on a630 until the issue is understood.
> 
> Reported-by: Caleb Connolly <caleb.connolly@linaro.org>
> Fixes: 9bc95570175a ("drm/msm: Devfreq tuning")
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>   drivers/gpu/drm/msm/adreno/adreno_gpu.c |  3 +++
>   drivers/gpu/drm/msm/msm_gpu.h           |  2 ++
>   drivers/gpu/drm/msm/msm_gpu_devfreq.c   | 12 ++++++++++++
>   3 files changed, 17 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.c b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> index 748665232d29..9fd08b413010 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> @@ -945,6 +945,9 @@ int adreno_gpu_init(struct drm_device *drm, struct platform_device *pdev,
>   	pm_runtime_use_autosuspend(dev);
>   	pm_runtime_enable(dev);
>   
> +	if (adreno_is_a630(adreno_gpu))
> +		gpu->devfreq.disable_freq_clamping = true;
> +
>   	return msm_gpu_init(drm, pdev, &adreno_gpu->base, &funcs->base,
>   			adreno_gpu->info->name, &adreno_gpu_config);
>   }
> diff --git a/drivers/gpu/drm/msm/msm_gpu.h b/drivers/gpu/drm/msm/msm_gpu.h
> index 0e4b45bff2e6..7e11b667f939 100644
> --- a/drivers/gpu/drm/msm/msm_gpu.h
> +++ b/drivers/gpu/drm/msm/msm_gpu.h
> @@ -112,6 +112,8 @@ struct msm_gpu_devfreq {
>   	 * it is inactive.
>   	 */
>   	unsigned long idle_freq;
> +
> +	bool disable_freq_clamping;
>   };
>   
>   struct msm_gpu {
> diff --git a/drivers/gpu/drm/msm/msm_gpu_devfreq.c b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> index 0a1ee20296a2..a832af436251 100644
> --- a/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> +++ b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> @@ -94,6 +94,12 @@ void msm_devfreq_init(struct msm_gpu *gpu)
>   	if (!gpu->funcs->gpu_busy)
>   		return;
>   
> +	/* Revert to previous polling interval if we aren't using freq clamping
> +	 * to preserve previous behavior
> +	 */
> +	if (gpu->devfreq.disable_freq_clamping)
> +		msm_devfreq_profile.polling_ms = 10;
> +
>   	msm_devfreq_profile.initial_freq = gpu->fast_rate;
>   
>   	/*
> @@ -151,6 +157,9 @@ void msm_devfreq_active(struct msm_gpu *gpu)
>   	unsigned int idle_time;
>   	unsigned long target_freq = df->idle_freq;
>   
> +	if (gpu->devfreq.disable_freq_clamping)
> +		return;
> +
>   	/*
>   	 * Hold devfreq lock to synchronize with get_dev_status()/
>   	 * target() callbacks
> @@ -186,6 +195,9 @@ void msm_devfreq_idle(struct msm_gpu *gpu)
>   	struct msm_gpu_devfreq *df = &gpu->devfreq;
>   	unsigned long idle_freq, target_freq = 0;
>   
> +	if (gpu->devfreq.disable_freq_clamping)
> +		return;
> +
>   	/*
>   	 * Hold devfreq lock to synchronize with get_dev_status()/
>   	 * target() callbacks
> 

-- 
Kind Regards,
Caleb (they/them)