Re: [PATCH v7 08/17] drm/panfrost: Split subsystem init/reset from interrupt enablement

["Adrián Larumbe" <adrian.larumbe@collabora.com>]

On 01.09.2026 15:08, Boris Brezillon wrote:
> On Fri, 28 Aug 2026 21:56:48 +0100
> Adrián Larumbe <adrian.larumbe@collabora.com> wrote:
> 
> > Because MMU interrupts are only enabled when the device is reset, it
> > happened that after DRM device registration, the very first job targeting
> > the tiler heap BO would always time out. The reason is the reset sequence
> > is only part of PM runtime resume, which is not called explicitly at driver
> > probe time, and an actual reset work item manually triggered after a HW
> > error.
> > 
> > I have attempted a somewhat drastic solution, which is completely
> > decoupling GPU/MMU/JM subsystem initialisation and reset from interrupt
> > enablement, so that we can handle IRQ toggling a bit more flexibly.
> > 
> > To this end:
> > - Ensure every subsystem with its own IRQ has an 'enable interrupts'
> > method, and that it doesn't enable them anywhere else.
> > - Force IRQ masking at MMU reset time. Up until, now, panfrost_mmu_reset()
> > was clearing the MMU IRQ suspension bit, but at no point that is set during
> > the reset sequence.
> > 
> > Then manually enable all interrupts when the device is fully initialised at
> > probe time, right before DRM device registration, or after the reset
> > sequence is complete. Also disable all interrupts at device remove time,
> > so that their IRQs can be sync'ed right before tearing the device down.
> > 
> > Fixes: 635430797d3f ("drm/panfrost: Rework runtime PM initialization")
> > Fixes: 876b15d2c88d ("drm/panfrost: Fix module unload")
> > Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> > ---
> >  drivers/gpu/drm/panfrost/panfrost_device.c | 40 ++++++++++++++++++++++--------
> >  drivers/gpu/drm/panfrost/panfrost_device.h |  3 ++-
> >  drivers/gpu/drm/panfrost/panfrost_gpu.c    | 19 ++++++++------
> >  drivers/gpu/drm/panfrost/panfrost_gpu.h    |  2 ++
> >  drivers/gpu/drm/panfrost/panfrost_job.c    |  7 +++---
> >  drivers/gpu/drm/panfrost/panfrost_mmu.c    |  9 +++++--
> >  drivers/gpu/drm/panfrost/panfrost_mmu.h    |  2 ++
> >  7 files changed, 56 insertions(+), 26 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> > index 9e02fb5f73c8..99f7da2180f9 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> > @@ -226,6 +226,27 @@ static int panfrost_pm_domain_init(struct panfrost_device *pfdev)
> >  	return err;
> >  }
> >  
> > +void panfrost_device_enable_int(struct panfrost_device *pfdev)
> > +{
> > +	panfrost_gpu_enable_interrupts(pfdev);
> > +	panfrost_mmu_enable_interrupts(pfdev);
> > +	panfrost_jm_enable_interrupts(pfdev);
> > +}
> > +
> > +static void panfrost_device_enable_hw(struct panfrost_device *pfdev)
> > +{
> > +	panfrost_device_enable_int(pfdev);
> > +	panfrost_devfreq_resume(pfdev);
> > +}
> > +
> > +static void panfrost_device_disable_hw(struct panfrost_device *pfdev)
> > +{
> > +	panfrost_devfreq_suspend(pfdev);
> > +	panfrost_jm_suspend_irq(pfdev);
> > +	panfrost_mmu_suspend_irq(pfdev);
> > +	panfrost_gpu_suspend_irq(pfdev);
> 
> Hm, I think I'd prefer if those suspend/resume_irq() were hidden in
> some subcomponent panfrost_<subcomp>_suspend,resume() helpers. And
> then we just have to resume/suspend component in the right order
> instead of treating IRQs as a standalone object (enabling/disabling
> only makes sense if the subcomponent handling those interrupts is
> resumed/suspended).

I thought it would only make sense to enable interupts for a given subsystem
when all the other subsystems are also resumed or initialised. This was prompted
by Sashiko warning of the possibility of spurious interrupts causing a handler
to be run when one of the subsystems it touches on hasn't yet been initialised.

Adrian Larumbe