Re: [PATCH 05/11] drm/panthor: Fix theoretical IOMEM access in suspended state

[Liviu Dudau <liviu.dudau@arm.com>]

On Thu, Jun 25, 2026 at 02:40:31PM +0200, Boris Brezillon wrote:
> In theory, our hardirq handler can be called while the device (and
> thus the panthor_irq) is suspended, because the IRQ line is shared.
> In practice though, in all the designs we've seen, the line is only
> shared within the GPU, and because sub-component suspend state is
> consistent (all-suspended or all-resumed), we shouldn't end up with
> an interrupt triggered while we're suspended.
> 
> Fix the problem anyway, if nothing else, for our sanity.
> 
> Fixes: 0b2d86670a84 ("drm/panthor: Rework panthor_irq::suspended into panthor_irq::state")
> Reported-by: sashiko-bot@kernel.org
> Closes: https://sashiko.dev/#/patchset/20260625-panthor-signal-from-irq-v4-0-3d2908912afa@collabora.com?part=1
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_device.h | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> index 35679bfa1f3a..a39386bd6382 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.h
> +++ b/drivers/gpu/drm/panthor/panthor_device.h
> @@ -512,9 +512,6 @@ static irqreturn_t panthor_ ## __name ## _irq_raw_handler(int irq, void *data)
>  	struct panthor_irq *pirq = data;							\
>  	enum panthor_irq_state old_state;							\
>  												\
> -	if (!gpu_read(pirq->iomem, INT_STAT))							\
> -		return IRQ_NONE;								\
> -												\
>  	guard(spinlock_irqsave)(&pirq->mask_lock);						\
>  	old_state = atomic_cmpxchg(&pirq->state,						\
>  				   PANTHOR_IRQ_STATE_ACTIVE,					\
> @@ -522,6 +519,13 @@ static irqreturn_t panthor_ ## __name ## _irq_raw_handler(int irq, void *data)
>  	if (old_state != PANTHOR_IRQ_STATE_ACTIVE)						\
>  		return IRQ_NONE;								\
>  												\
> +	if (!gpu_read(pirq->iomem, INT_STAT)) {							\
> +		atomic_cmpxchg(&pirq->state,							\
> +			       PANTHOR_IRQ_STATE_PROCESSING,					\
> +			       PANTHOR_IRQ_STATE_ACTIVE);					\
> +		return IRQ_NONE;								\
> +	}											\

Hmm,

I get it that you're trying to revert the effect of the previous atomic_cmpxchg() here but it feels
like a better option would be to not do the swap at all if the state is not ACTIVE.

Best regards,
Liviu

> +												\
>  	gpu_write(pirq->iomem, INT_MASK, 0);							\
>  	return IRQ_WAKE_THREAD;									\
>  }												\
> 
> -- 
> 2.54.0
> 

-- 
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