[Intel-xe] [PATCH] drm/xe: fix mcr semaphore locking for MTL

[Matt Roper]

On Wed, Jul 26, 2023 at 03:25:28PM -0700, Daniele Ceraolo Spurio wrote:
> in commit 8604f978f45b ("drm/xe: Convert xe_mmio_wait32 to us so we can
> stop using wait_for_us.") the mcr semaphore register read was
> accidentally switched from waiting for the register to go to 1 to
> waiting for the register to go to 0, so we need to flip it back.
> 
> Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> Cc: Matthew Brost <matthew.brost at intel.com>

Reviewed-by: Matt Roper <matthew.d.roper at intel.com>

> ---
>  drivers/gpu/drm/xe/xe_gt_mcr.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_gt_mcr.c b/drivers/gpu/drm/xe/xe_gt_mcr.c
> index c56815af0686..9eb7a6a1348d 100644
> --- a/drivers/gpu/drm/xe/xe_gt_mcr.c
> +++ b/drivers/gpu/drm/xe/xe_gt_mcr.c
> @@ -420,10 +420,11 @@ static void mcr_lock(struct xe_gt *gt)
>  	/*
>  	 * Starting with MTL we also need to grab a semaphore register
>  	 * to synchronize with external agents (e.g., firmware) that now
> -	 * shares the same steering control register.
> +	 * shares the same steering control register. The semaphore is obtained
> +	 * when a read to the relevant register returns 1.
>  	 */
>  	if (GRAPHICS_VERx100(xe) >= 1270)
> -		ret = xe_mmio_wait32(gt, STEER_SEMAPHORE, 0, 0x1, 10, NULL,
> +		ret = xe_mmio_wait32(gt, STEER_SEMAPHORE, 0x1, 0x1, 10, NULL,
>  				     true);
>  
>  	drm_WARN_ON_ONCE(&xe->drm, ret == -ETIMEDOUT);
> @@ -431,7 +432,7 @@ static void mcr_lock(struct xe_gt *gt)
>  
>  static void mcr_unlock(struct xe_gt *gt)
>  {
> -	/* Release hardware semaphore */
> +	/* Release hardware semaphore - this is done by writing 1 to the register */
>  	if (GRAPHICS_VERx100(gt_to_xe(gt)) >= 1270)
>  		xe_mmio_write32(gt, STEER_SEMAPHORE, 0x1);
>  
> -- 
> 2.41.0
> 

-- 
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation