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

[AngeloGioacchino Del Regno]

Il 31/10/23 04:18, Chen-Yu Tsai ha scritto:
> 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).

I don't expect a need to do mask checking, but I don't expect the opposite either..
...this could happen in the future, or maybe not, and this becomes a bool, even.

That's why I went with a u8 :-)

Let's keep it flexible.

Thanks,
Angelo

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