Re: [PATCH v2 11/11] drm/panthor: Process GPU events in IRQ context

[Chia-I Wu <olvaffe@gmail.com>]

On Tue, May 12, 2026 at 5:09 AM Boris Brezillon
<boris.brezillon@collabora.com> wrote:
>
> On Tue, 12 May 2026 13:37:41 +0200
> Boris Brezillon <boris.brezillon@collabora.com> wrote:
>
> > The current panthor_gpu_irq_handler() logic is already IRQ-safe
> > (no sleep or sleeping locks, spinlocks taken with irqsave in other
> > contexts, etc), so let's toggle the switch and make it an hard IRQ
> > handler.
> >
> > Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> > ---
> >  drivers/gpu/drm/panthor/panthor_gpu.c | 15 ++++++++-------
> >  1 file changed, 8 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panthor/panthor_gpu.c b/drivers/gpu/drm/panthor/panthor_gpu.c
> > index b9c51f8a051d..04c8f23baf3f 100644
> > --- a/drivers/gpu/drm/panthor/panthor_gpu.c
> > +++ b/drivers/gpu/drm/panthor/panthor_gpu.c
> > @@ -86,10 +86,15 @@ static void panthor_gpu_l2_config_set(struct panthor_device *ptdev)
> >       gpu_write(gpu->iomem, GPU_L2_CONFIG, l2_config);
> >  }
> >
> > -static void panthor_gpu_irq_handler(struct panthor_irq *pirq, u32 status)
> > +static irqreturn_t panthor_gpu_irq_raw_handler(int irq, void *data)
> >  {
> > +     struct panthor_irq *pirq = data;
> >       struct panthor_device *ptdev = pirq->ptdev;
> >       struct panthor_gpu *gpu = ptdev->gpu;
> > +     u32 status = gpu_read(gpu->irq.iomem, INT_STAT);
> > +
> > +     if (!status)
> > +             return IRQ_NONE;
> >
>
> Forgot to add the pirq state transition here:
>
>        scoped_guard(spinlock_irqsave, &pirq->mask_lock) {
>                if (pirq->state != PANTHOR_IRQ_STATE_ACTIVE)
>                        return IRQ_NONE;
>
>                pirq->state = PANTHOR_IRQ_STATE_PROCESSING;
>        }
>
> >       gpu_write(gpu->irq.iomem, INT_CLEAR, status);
> >
> > @@ -115,11 +120,8 @@ static void panthor_gpu_irq_handler(struct panthor_irq *pirq, u32 status)
> >               ptdev->gpu->pending_reqs &= ~status;
> >               wake_up_all(&ptdev->gpu->reqs_acked);
> >       }
> > -}
> >
> > -static irqreturn_t panthor_gpu_irq_threaded_handler(int irq, void *data)
> > -{
> > -     return panthor_irq_default_threaded_handler(data, panthor_gpu_irq_handler);
>
> and restore it here:
>
>        scoped_guard(spinlock_irqsave, &pirq->mask_lock) {
>                if (pirq->state == PANTHOR_IRQ_STATE_PROCESSING)
>                        pirq->state = PANTHOR_IRQ_STATE_ACTIVE;
>        }
>
It looks like we can get rid of state transitions if
panthor_irq_{enable,disable}_events updates INT_MASK directly when the
handler is not threaded. Hm, we can even make pirq->state atomic again
to get rid of locking.

> > +     return IRQ_HANDLED;
> >  }
> >
> >  /**
> > @@ -176,8 +178,7 @@ int panthor_gpu_init(struct panthor_device *ptdev)
> >       ret = panthor_irq_request(ptdev, &ptdev->gpu->irq, irq,
> >                                 GPU_INTERRUPTS_MASK,
> >                                 ptdev->iomem + GPU_INT_BASE, "gpu",
> > -                               panthor_irq_default_raw_handler,
> > -                               panthor_gpu_irq_threaded_handler);
> > +                               panthor_gpu_irq_raw_handler, NULL);
> >       if (ret)
> >               return ret;
> >
> >
>