[PATCH] drm/i915/gt: Add delay to let engine resumes properly

[Krzysztof Karas]

Hi Nitin,

[...]

> -		if (!stop_ring(engine)) {
> +		/*
> +		 * Sometimes engine head failed to set to zero even after writing into it.
> +		 * Use wait_for_atomic() with 20ms delay to let engine resumes from
> +		 * correct RING_HEAD. Experimented different values and determined
> +		 * that 20ms works best based on testing.
> +		 */
> +		if (wait_for_atomic((!stop_ring(engine) == 0), 20)) {
>  			drm_err(&engine->i915->drm,
>  				"failed to set %s head to zero "
>  				"ctl %08x head %08x tail %08x start %08x\n",

I am wondering if xcs_resume() calling stop_ring() too would
benefit from having this timeout on hand as well. That would
require moving wait_for_atomic((!stop_ring(engine) == 0), 20)
along with your comment to a separate wrapper function.
What do you think?

Best Regards
Krzysztof