Re: [PATCH v3 2/3] drm/panthor: Fix ordering in _irq_suspend()

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

On Tue, Mar 26, 2024 at 12:12:04PM +0100, Boris Brezillon wrote:
> Make sure we set suspended=true last to avoid generating an irq storm
> in the unlikely case where an IRQ happens between the suspended=true
> assignment and the _INT_MASK update.
> 
> We also move the mask=0 assignment before writing to the _INT_MASK
> register to prevent the thread handler from unmasking the interrupt
> behind our back. This means we might lose events if there were some
> pending when we get to suspend the IRQ, but that's fine.
> The synchronize_irq() we have in the _irq_suspend() path was not
> there to make sure all IRQs are processed, just to make sure we don't
> have registers accesses coming from the irq handlers after
> _irq_suspend() has been called. If there's a need to have all pending
> IRQs processed, it should happen before _irq_suspend() is called.
> 
> v3:
> - Add Steve's R-b
> 
> v2:
> - New patch
> 
> Fixes: 5fe909cae118 ("drm/panthor: Add the device logical block")
> Reported-by: Steven Price <steven.price@arm.com>
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> Reviewed-by: Steven Price <steven.price@arm.com>

Acked-by: Liviu Dudau <liviu.dudau@arm.com>

Best regards,
Liviu

> ---
>  drivers/gpu/drm/panthor/panthor_device.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> index 7ee4987a3796..3a930a368ae1 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.h
> +++ b/drivers/gpu/drm/panthor/panthor_device.h
> @@ -325,7 +325,7 @@ static inline void panthor_ ## __name ## _irq_suspend(struct panthor_irq *pirq)
>  {												\
>  	int cookie;										\
>  												\
> -	atomic_set(&pirq->suspended, true);							\
> +	pirq->mask = 0;										\
>  												\
>  	if (drm_dev_enter(&pirq->ptdev->base, &cookie)) {					\
>  		gpu_write(pirq->ptdev, __reg_prefix ## _INT_MASK, 0);				\
> @@ -333,7 +333,7 @@ static inline void panthor_ ## __name ## _irq_suspend(struct panthor_irq *pirq)
>  		drm_dev_exit(cookie);								\
>  	}											\
>  												\
> -	pirq->mask = 0;										\
> +	atomic_set(&pirq->suspended, true);							\
>  }												\
>  												\
>  static inline void panthor_ ## __name ## _irq_resume(struct panthor_irq *pirq, u32 mask)	\
> -- 
> 2.44.0
> 

-- 
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