Re: [PATCH 1/1] drm/xe: Restore engine registers before restarting schedulers after GT reset

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Dec 05, 2025 at 05:55:29AM +0100, Jan Maslak wrote:
> During GT reset recovery in do_gt_restart(), xe_uc_start() was called
> before xe_reg_sr_apply_mmio() restored engine-specific registers. This
> created a race window where the scheduler could run jobs before hardware
> state was fully restored.
> 
> This caused failures in eudebug tests (xe_exec_sip_eudebug@breakpoint-
> waitsip-*) where TD_CTL register (containing TD_CTL_GLOBAL_DEBUG_ENABLE)
> wasn't restored before jobs started executing. Breakpoints would fail to
> trigger SIP entry because the debug enable bit wasn't set yet.
> 
> Fix by moving engine register restoration before xe_uc_start(), ensuring
> all hardware state is fully restored before any jobs can be scheduled.
> 
> Signed-off-by: Jan Maslak <jan.maslak@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_gt.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_gt.c b/drivers/gpu/drm/xe/xe_gt.c
> index 7caf781ba9e8..17642d71f98f 100644
> --- a/drivers/gpu/drm/xe/xe_gt.c
> +++ b/drivers/gpu/drm/xe/xe_gt.c
> @@ -771,13 +771,14 @@ static int do_gt_restart(struct xe_gt *gt)
>  		xe_gt_sriov_pf_init_hw(gt);
>  
>  	xe_mocs_init(gt);
> -	err = xe_uc_start(&gt->uc);
> -	if (err)
> -		return err;
>  
>  	for_each_hw_engine(hwe, gt, id)
>  		xe_reg_sr_apply_mmio(&hwe->reg_sr, gt);
>  
> +	err = xe_uc_start(&gt->uc);
> +	if (err)
> +		return err;
> +
>  	/* Get CCS mode in sync between sw/hw */
>  	xe_gt_apply_ccs_mode(gt);
>  

I think you need to move this xe_gt_apply_ccs_mode as that is also
writing MMIO registers that should be configured before bring the chip
back to a live state.

Also I think you need a fixes tag here as this is pretty clearly a
bug.

Matt

> -- 
> 2.34.1
>