Re: [PATCH 1/2] drm/panfrost: Add PM runtime flags

[Philippe Simons]

On 3/31/25 12:32, Steven Price wrote:
> On 27/03/2025 12:36, Andre Przywara wrote:
> > On Thu, 13 Mar 2025 00:23:18 +0100
> > Philippe Simons <simons.philippe@xxxxxxxxx> wrote:
> >
> > Hi Rob, Boris, Steven,
> >
> > > When the GPU is the only device attached to a single power domain,
> > > core genpd disable and enable it when gpu enter and leave runtime suspend.
> > >
> > > Some power-domain requires a sequence before disabled,
> > > and the reverse when enabled.
> > >
> > > Add PM flags for CLK and RST, and implement in
> > > panfrost_device_runtime_suspend/resume.
> > So some Mali configuration and integration manual I am looking at says
> > that this sequence should be always observed, as the powerdown sequence
> > would include disabling the clocks first, then asserting the reset, then
> > turning the power switches off (and the inverse sequence on powerup).
> >
> > So should we make this unconditional, not depending on implementation
> > specific flags?
> I think you're right, this probably should be unconditional. My only
> reservation is that "it works" currently and we'd need to test this
> doesn't cause regressions on existing platforms. So unless someone with
> a reasonable board farm is able to do that testing I think this solution
> is reasonable. So:

Should I merge both flags together then ? something like GPU_PM_RT ?

> Reviewed-by: Steven Price <steven.price@xxxxxxx>
>
> > And also I am wondering if panfrost_device_init() gets this wrong as well?
> > As I see it enabling clock first, then reset, then pm_domain, where it
> > should be exactly the opposite?
> I agree, that looks very wrong - the power needs to be enabled before
> reset is deasserted. I'm somewhat surprised we've got away with that.
> Fancy writing a patch? ;)
>
> Steve
>
> > Cheers,
> > Andre
> >
> > > Signed-off-by: Philippe Simons <simons.philippe@xxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/panfrost/panfrost_device.c | 37 ++++++++++++++++++++++
> > >   drivers/gpu/drm/panfrost/panfrost_device.h |  4 +++
> > >   2 files changed, 41 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> > > index a45e4addcc19..189ad2ad2b32 100644
> > > --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> > > +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> > > @@ -406,11 +406,38 @@ void panfrost_device_reset(struct panfrost_device *pfdev)
> > >   static int panfrost_device_runtime_resume(struct device *dev)
> > >   {
> > >   	struct panfrost_device *pfdev = dev_get_drvdata(dev);
> > > +	int ret;
> > > +
> > > +	if (pfdev->comp->pm_features & BIT(GPU_PM_RT_RST_ASRT)) {
> > > +		ret = reset_control_deassert(pfdev->rstc);
> > > +		if (ret)
> > > +			return ret;
> > > +	}
> > > +
> > > +	if (pfdev->comp->pm_features & BIT(GPU_PM_RT_CLK_DIS)) {
> > > +		ret = clk_enable(pfdev->clock);
> > > +		if (ret)
> > > +			goto err_clk;
> > > +
> > > +		if (pfdev->bus_clock) {
> > > +			ret = clk_enable(pfdev->bus_clock);
> > > +			if (ret)
> > > +				goto err_bus_clk;
> > > +		}
> > > +	}
> > >   
> > >   	panfrost_device_reset(pfdev);
> > >   	panfrost_devfreq_resume(pfdev);
> > >   
> > >   	return 0;
> > > +
> > > +err_bus_clk:
> > > +	if (pfdev->comp->pm_features & BIT(GPU_PM_RT_CLK_DIS))
> > > +		clk_disable(pfdev->clock);
> > > +err_clk:
> > > +	if (pfdev->comp->pm_features & BIT(GPU_PM_RT_RST_ASRT))
> > > +		reset_control_assert(pfdev->rstc);
> > > +	return ret;
> > >   }
> > >   
> > >   static int panfrost_device_runtime_suspend(struct device *dev)
> > > @@ -426,6 +453,16 @@ static int panfrost_device_runtime_suspend(struct device *dev)
> > >   	panfrost_gpu_suspend_irq(pfdev);
> > >   	panfrost_gpu_power_off(pfdev);
> > >   
> > > +	if (pfdev->comp->pm_features & BIT(GPU_PM_RT_CLK_DIS)) {
> > > +		if (pfdev->bus_clock)
> > > +			clk_disable(pfdev->bus_clock);
> > > +
> > > +		clk_disable(pfdev->clock);
> > > +	}
> > > +
> > > +	if (pfdev->comp->pm_features & BIT(GPU_PM_RT_RST_ASRT))
> > > +		reset_control_assert(pfdev->rstc);
> > > +
> > >   	return 0;
> > >   }
> > >   
> > > diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> > > index cffcb0ac7c11..f372d4819262 100644
> > > --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> > > +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> > > @@ -36,10 +36,14 @@ enum panfrost_drv_comp_bits {
> > >    * enum panfrost_gpu_pm - Supported kernel power management features
> > >    * @GPU_PM_CLK_DIS:  Allow disabling clocks during system suspend
> > >    * @GPU_PM_VREG_OFF: Allow turning off regulators during system suspend
> > > + * @GPU_PM_RT_CLK_DIS: Allow disabling clocks during system runtime suspend
> > > + * @GPU_PM_RST_ASRT: Allow asserting the reset control during runtime suspend
> > >    */
> > >   enum panfrost_gpu_pm {
> > >   	GPU_PM_CLK_DIS,
> > >   	GPU_PM_VREG_OFF,
> > > +	GPU_PM_RT_CLK_DIS,
> > > +	GPU_PM_RT_RST_ASRT
> > >   };
> > >   
> > >   struct panfrost_features {