Re: [PATCH v2 3/3] drm/panfrost: Synchronize and disable interrupts before powering off

[AngeloGioacchino Del Regno]

Il 28/11/23 15:06, Boris Brezillon ha scritto:
> On Tue, 28 Nov 2023 13:45:10 +0100
> AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
> wrote:
>
> > To make sure that we don't unintentionally perform any unclocked and/or
> > unpowered R/W operation on GPU registers, before turning off clocks and
> > regulators we must make sure that no GPU, JOB or MMU ISR execution is
> > pending: doing that required to add a mechanism to synchronize the
> > interrupts on suspend.
> >
> > Add functions panfrost_{gpu,job,mmu}_suspend_irq() which will perform
> > interrupts masking and ISR execution synchronization, and then call
> > those in the panfrost_device_runtime_suspend() handler in the exact
> > sequence of job (may require mmu!) -> mmu -> gpu.
> >
> > As a side note, JOB and MMU suspend_irq functions needed some special
> > treatment: as their interrupt handlers will unmask interrupts, it was
> > necessary to add a bitmap for "is_suspending" which is used to address
> > the possible corner case of unintentional IRQ unmasking because of ISR
> > execution after a call to synchronize_irq().
> >
> > Of course, unmasking the interrupts is being done as part of the reset
> > happening during runtime_resume(): since we're anyway resuming all of
> > GPU, JOB, MMU, the only additional action is to zero out the newly
> > introduced `is_suspending` bitmap directly in the resume handler, as
> > to avoid adding panfrost_{job,mmu}_resume_irq() function just for
> > clearing own bits, especially because it currently makes way more sense
> > to just zero out the bitmap.
> >
> > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/panfrost/panfrost_device.c |  4 ++++
> >   drivers/gpu/drm/panfrost/panfrost_device.h |  7 +++++++
> >   drivers/gpu/drm/panfrost/panfrost_gpu.c    |  7 +++++++
> >   drivers/gpu/drm/panfrost/panfrost_gpu.h    |  1 +
> >   drivers/gpu/drm/panfrost/panfrost_job.c    | 18 +++++++++++++++---
> >   drivers/gpu/drm/panfrost/panfrost_job.h    |  1 +
> >   drivers/gpu/drm/panfrost/panfrost_mmu.c    | 17 ++++++++++++++---
> >   drivers/gpu/drm/panfrost/panfrost_mmu.h    |  1 +
> >   8 files changed, 50 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> > index c90ad5ee34e7..ed34aa55a7da 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> > @@ -407,6 +407,7 @@ static int panfrost_device_runtime_resume(struct device *dev)
> >   {
> >   	struct panfrost_device *pfdev = dev_get_drvdata(dev);
> >   
> > +	bitmap_zero(pfdev->is_suspending, PANFROST_COMP_BIT_MAX);
>
> I would let each sub-block clear their bit in the reset path, since
> that's where the IRQs are effectively unmasked.


Honestly I wouldn't like seeing that: the reason is that this is something that
is done *for* suspend/resume and only for that, while reset may be called out of
the suspend/resume handlers.

I find clearing the suspend bits in the HW reset path a bit confusing, especially
when it is possible to avoid doing it there...

> >   	panfrost_device_reset(pfdev);
> >   	panfrost_devfreq_resume(pfdev);
> >   
> > @@ -421,6 +422,9 @@ static int panfrost_device_runtime_suspend(struct device *dev)
> >   		return -EBUSY;
> >   
> >   	panfrost_devfreq_suspend(pfdev);
> > +	panfrost_job_suspend_irq(pfdev);
> > +	panfrost_mmu_suspend_irq(pfdev);
> > +	panfrost_gpu_suspend_irq(pfdev);
> >   	panfrost_gpu_power_off(pfdev);
> >   
> >   	return 0;
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> > index 54a8aad54259..29f89f2d3679 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> > +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> > @@ -25,6 +25,12 @@ struct panfrost_perfcnt;
> >   #define NUM_JOB_SLOTS 3
> >   #define MAX_PM_DOMAINS 5
> >   
> > +enum panfrost_drv_comp_bits {
> > +	PANFROST_COMP_BIT_MMU,
> > +	PANFROST_COMP_BIT_JOB,
> > +	PANFROST_COMP_BIT_MAX
> > +};
> > +
> >   /**
> >    * enum panfrost_gpu_pm - Supported kernel power management features
> >    * @GPU_PM_CLK_DIS:  Allow disabling clocks during system suspend
> > @@ -109,6 +115,7 @@ struct panfrost_device {
> >   
> >   	struct panfrost_features features;
> >   	const struct panfrost_compatible *comp;
> > +	DECLARE_BITMAP(is_suspending, PANFROST_COMP_BIT_MAX);
>
> nit: Maybe s/is_suspending/suspended_irqs/, given the state remains
> until the device is resumed.

If we keep the `is_suspending` name, we can use this one more generically in
case we ever need to, what do you think?

Cheers,
Angelo