Re: [PATCH v4 10/18] drm/panthor: Check AS state before disabling

[Adrian Larumbe <adrian.larumbe@collabora.com>]

Reviewed-by: Adrián Larumbe <adrian.larumbe@collabora.com>

On 26.08.2026 16:56, Boris Brezillon wrote:
> Use TRANSTAB == 0 as a way to detect if an AS slot is idle. This
> allows us to make panthor_mmu_as_disable() a NOP when it's called
> after a SOFT_RESET, which will be needed for our unplug rework.
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_mmu.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index 3d9f9bf29e1d..58f0bd2ac7a2 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -640,6 +640,10 @@ static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 slot,
>  
>  	lockdep_assert_held(&ptdev->mmu->as.slots_lock);
>  
> +	/* The AS was disabled already, nothing to do. */
> +	if (!gpu_read64(mmu->iomem, AS_TRANSTAB(slot)))
> +		return 0;
> +
>  	panthor_irq_disable_events(&ptdev->mmu->irq,
>  				   panthor_mmu_as_fault_mask(ptdev, slot));
>  
> @@ -662,11 +666,17 @@ static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 slot,
>  	if (recycle_slot)
>  		return 0;
>  
> -	gpu_write64(mmu->iomem, AS_TRANSTAB(slot), 0);
> -	gpu_write64(mmu->iomem, AS_MEMATTR(slot), 0);
>  	gpu_write64(mmu->iomem, AS_TRANSCFG(slot), AS_TRANSCFG_ADRMODE_UNMAPPED);
> +	ret = as_send_cmd_and_wait(ptdev, slot, AS_COMMAND_UPDATE);
> +	if (ret)
> +		return ret;
>  
> -	return as_send_cmd_and_wait(ptdev, slot, AS_COMMAND_UPDATE);
> +	/* We reset the other fields late to ensure that, if something fails,
> +	 * the page table is considered active (TRANSTAB != NULL).
> +	 */
> +	gpu_write64(mmu->iomem, AS_MEMATTR(slot), 0);
> +	gpu_write64(mmu->iomem, AS_TRANSTAB(slot), 0);
> +	return 0;
>  }
>  
>  static u32 panthor_mmu_fault_mask(struct panthor_device *ptdev, u32 value)
> 
> -- 
> 2.55.0

Adrian Larumbe