Re: [PATCH 1/3] drm/panfrost: Clear MMU irqs before handling the fault

[Steven Price <steven.price@arm.com>]

On 01/02/2021 08:21, Boris Brezillon wrote:
> When a fault is handled it will unblock the GPU which will continue
> executing its shader and might fault almost immediately on a different
> page. If we clear interrupts after handling the fault we might miss new
> faults, so clear them before.
> 
> Cc: <stable@vger.kernel.org>
> Fixes: 187d2929206e ("drm/panfrost: Add support for GPU heap allocations")
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>

Good catch (although this oddly rings a bell - so perhaps it was me you 
discussed it with before)

Reviewed-by: Steven Price <steven.price@arm.com>

> ---
>   drivers/gpu/drm/panfrost/panfrost_mmu.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index 7c1b3481b785..904d63450862 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -593,6 +593,8 @@ static irqreturn_t panfrost_mmu_irq_handler_thread(int irq, void *data)
>   		access_type = (fault_status >> 8) & 0x3;
>   		source_id = (fault_status >> 16);
>   
> +		mmu_write(pfdev, MMU_INT_CLEAR, mask);
> +
>   		/* Page fault only */
>   		ret = -1;
>   		if ((status & mask) == BIT(i) && (exception_type & 0xF8) == 0xC0)
> @@ -616,8 +618,6 @@ static irqreturn_t panfrost_mmu_irq_handler_thread(int irq, void *data)
>   				access_type, access_type_name(pfdev, fault_status),
>   				source_id);
>   
> -		mmu_write(pfdev, MMU_INT_CLEAR, mask);
> -
>   		status &= ~mask;
>   	}
>   
>