linux-kernel - Re: [PATCH 2/2] drm/msm/gpu: Respect PM QoS constraints

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Message-ID: <CAD=FV=WBkGMXPvuLaQ0n2V3UgAQajvYg=dPwZNx-TnpXMV1bvw@mail.gmail.com>
Date:   Fri, 5 Nov 2021 13:49:30 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel@...ts.freedesktop.org,
        Rob Clark <robdclark@...omium.org>,
        David Airlie <airlied@...ux.ie>, linux-arm-msm@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        Sean Paul <sean@...rly.run>, freedreno@...ts.freedesktop.org
Subject: Re: [PATCH 2/2] drm/msm/gpu: Respect PM QoS constraints

Hi,

On Wed, Nov 3, 2021 at 1:59 PM Rob Clark <robdclark@...il.com> wrote:
>
> From: Rob Clark <robdclark@...omium.org>
>
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/gpu/drm/msm/msm_gpu_devfreq.c | 31 +++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_gpu_devfreq.c b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> index b24e5475cafb..427c55002f4d 100644
> --- a/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> +++ b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
> @@ -158,6 +158,33 @@ void msm_devfreq_suspend(struct msm_gpu *gpu)
>         devfreq_suspend_device(gpu->devfreq.devfreq);
>  }
>
> +static void set_target(struct msm_gpu *gpu, unsigned long freq)
> +{
> +       struct msm_gpu_devfreq *df = &gpu->devfreq;
> +       unsigned long min_freq, max_freq;
> +       u32 flags = 0;
> +
> +       /*
> +        * When setting the target freq internally, we need to apply PM QoS
> +        * constraints (such as cooling):
> +        */
> +       min_freq = dev_pm_qos_read_value(df->devfreq->dev.parent,
> +                                        DEV_PM_QOS_MIN_FREQUENCY);

Chatted with Rob offline about this, but to document on the lists for
those playing at home: the above function isn't exported to modules,
so this will fail with "allmodconfig".

In general this isn't the right approach here. I believe that the
right approach is to boost with freq_qos_update_request() and then
kick off a timer to stop boosting after a fixed period of time.


-Doug