Re: [Intel-gfx] [PATCH 1/6] drm/i915/gt: Sanitize GPU during prepare-to-suspend

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Wed, Feb 10, 2021 at 10:19:50PM +0000, Chris Wilson wrote:
> After calling intel_gt_suspend_prepare(), the driver starts to turn off
> various subsystems, such as clearing the GGTT, before calling
> intel_gt_suspend_late() to relinquish control over the GT. However, if
> we still have internal GPU state active as we clear the GGTT, the GPU
> may write back its internal state to the residual GGTT addresses that
> are now pointing into scratch. Let's reset the GPU to clear that
> internal state as soon we have idled the GPU in prepare-to-suspend.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/gt/intel_gt_pm.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.c b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> index 0bd303d2823e..f41612faa269 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> @@ -295,6 +295,9 @@ void intel_gt_suspend_prepare(struct intel_gt *gt)
>  	wait_for_suspend(gt);

you just wedged the gpu here...

>  
>  	intel_uc_suspend(&gt->uc);
> +
> +	/* Flush all the contexts and internal state before turning off GGTT */
> +	gt_sanitize(gt, false);

and now we are unsetting wedge here...

is this right?

>  }
>  
>  static suspend_state_t pm_suspend_target(void)
> @@ -337,7 +340,7 @@ void intel_gt_suspend_late(struct intel_gt *gt)
>  		intel_llc_disable(&gt->llc);
>  	}
>  
> -	gt_sanitize(gt, false);
> +	gt_sanitize(gt, false); /* Be paranoid, remove all residual GPU state */
>  
>  	GT_TRACE(gt, "\n");
>  }
> -- 
> 2.20.1
> 
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