Re: [PATCH 1/4] drm/panfrost: Implement ability to turn on/off GPU clocks in suspend

[Chen-Yu Tsai]

On Mon, Oct 30, 2023 at 9:23 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@xxxxxxxxxxxxx> wrote:
>
> Currently, the GPU is being internally powered off for runtime suspend
> and turned back on for runtime resume through commands sent to it, but
> note that the GPU doesn't need to be clocked during the poweroff state,
> hence it is possible to save some power on selected platforms.
>
> Add suspend and resume handlers for full system sleep and then add
> a new panfrost_gpu_pm enumeration and a pm_features variable in the
> panfrost_compatible structure: BIT(GPU_PM_CLK_DIS) will be used to
> enable this power saving technique only on SoCs that are able to
> safely use it.
>
> Note that this was implemented only for the system sleep case and not
> for runtime PM because testing on one of my MediaTek platforms showed
> issues when turning on and off clocks aggressively (in PM runtime),
> with the GPU locking up and unable to soft reset, eventually resulting
> in a full system lockup.
>
> Doing this only for full system sleep never showed issues in 3 days
> of testing by suspending and resuming the system continuously.
>
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/panfrost/panfrost_device.c | 61 ++++++++++++++++++++--
>  drivers/gpu/drm/panfrost/panfrost_device.h | 11 ++++
>  2 files changed, 68 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> index 28f7046e1b1a..2022ed76a620 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> @@ -403,7 +403,7 @@ void panfrost_device_reset(struct panfrost_device *pfdev)
>         panfrost_job_enable_interrupts(pfdev);
>  }
>
> -static int panfrost_device_resume(struct device *dev)
> +static int panfrost_device_runtime_resume(struct device *dev)
>  {
>         struct panfrost_device *pfdev = dev_get_drvdata(dev);
>
> @@ -413,7 +413,7 @@ static int panfrost_device_resume(struct device *dev)
>         return 0;
>  }
>
> -static int panfrost_device_suspend(struct device *dev)
> +static int panfrost_device_runtime_suspend(struct device *dev)
>  {
>         struct panfrost_device *pfdev = dev_get_drvdata(dev);
>
> @@ -426,5 +426,58 @@ static int panfrost_device_suspend(struct device *dev)
>         return 0;
>  }
>
> -EXPORT_GPL_RUNTIME_DEV_PM_OPS(panfrost_pm_ops, panfrost_device_suspend,
> -                             panfrost_device_resume, NULL);
> +static int panfrost_device_resume(struct device *dev)
> +{
> +       struct panfrost_device *pfdev = dev_get_drvdata(dev);
> +       int ret;
> +
> +       if (pfdev->comp->pm_features & BIT(GPU_PM_CLK_DIS)) {
> +               ret = clk_enable(pfdev->clock);
> +               if (ret)
> +                       return ret;
> +
> +               if (pfdev->bus_clock) {
> +                       ret = clk_enable(pfdev->bus_clock);
> +                       if (ret)
> +                               goto err_bus_clk;
> +               }
> +       }
> +
> +       ret = pm_runtime_force_resume(dev);
> +       if (ret)
> +               goto err_resume;
> +
> +       return 0;
> +
> +err_resume:
> +       if (pfdev->comp->pm_features & BIT(GPU_PM_CLK_DIS) && pfdev->bus_clock)
> +               clk_disable(pfdev->bus_clock);
> +err_bus_clk:
> +       if (pfdev->comp->pm_features & BIT(GPU_PM_CLK_DIS))
> +               clk_disable(pfdev->clock);
> +       return ret;
> +}
> +
> +static int panfrost_device_suspend(struct device *dev)
> +{
> +       struct panfrost_device *pfdev = dev_get_drvdata(dev);
> +       int ret;
> +
> +       ret = pm_runtime_force_suspend(dev);
> +       if (ret)
> +               return ret;
> +
> +       if (pfdev->comp->pm_features & BIT(GPU_PM_CLK_DIS)) {
> +               clk_disable(pfdev->clock);
> +
> +               if (pfdev->bus_clock)
> +                       clk_disable(pfdev->bus_clock);
> +       }
> +
> +       return 0;
> +}
> +
> +EXPORT_GPL_DEV_PM_OPS(panfrost_pm_ops) = {
> +       RUNTIME_PM_OPS(panfrost_device_runtime_suspend, panfrost_device_runtime_resume, NULL)
> +       SYSTEM_SLEEP_PM_OPS(panfrost_device_suspend, panfrost_device_resume)
> +};
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> index 1ef38f60d5dc..d7f179eb8ea3 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> @@ -25,6 +25,14 @@ struct panfrost_perfcnt;
>  #define NUM_JOB_SLOTS 3
>  #define MAX_PM_DOMAINS 5
>
> +/**
> + * enum panfrost_gpu_pm - Supported kernel power management features
> + * @GPU_PM_CLK_DIS:  Allow disabling clocks during system suspend
> + */
> +enum panfrost_gpu_pm {
> +       GPU_PM_CLK_DIS,
> +};
> +
>  struct panfrost_features {
>         u16 id;
>         u16 revision;
> @@ -75,6 +83,9 @@ struct panfrost_compatible {
>
>         /* Vendor implementation quirks callback */
>         void (*vendor_quirk)(struct panfrost_device *pfdev);
> +
> +       /* Allowed PM features */
> +       u8 pm_features;

Nit: I'd just use bitfields. They are easier to set and get without
extra macros, and the naming would be self-explanatory. Unless you
expect a need to do mask checking (though the compiler might be able
to optimize this).

ChenYu

>  };
>
>  struct panfrost_device {
> --
> 2.42.0
>