Re: [Intel-gfx] [PATCH] drm/i915/gt: Reset execlists registers before HWSP

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Upon gt resume, we first poison then sanitize the engine. However, our
> testing shows that gen9 will very rarely retain the poisoned value from
> the HWSP mappings of the execlists status registers. This suggests that
> it is reading back from the HWSP, so rejig the register reset.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Acked-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/gt/intel_lrc.c | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 3d0e0894c015..a7d644a21f14 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -3924,6 +3924,14 @@ static void reset_csb_pointers(struct intel_engine_cs *engine)
>  
>  	ring_set_paused(engine, 0);
>  
> +	/*
> +	 * Sometimes Icelake forgets to reset its pointers on a GPU reset.
> +	 * Bludgeon them with a mmio update to be sure.
> +	 */
> +	ENGINE_WRITE(engine, RING_CONTEXT_STATUS_PTR,
> +		     reset_value << 8 | reset_value);
> +	ENGINE_POSTING_READ(engine, RING_CONTEXT_STATUS_PTR);
> +
>  	/*
>  	 * After a reset, the HW starts writing into CSB entry [0]. We
>  	 * therefore have to set our HEAD pointer back one entry so that
> @@ -3937,16 +3945,15 @@ static void reset_csb_pointers(struct intel_engine_cs *engine)
>  	WRITE_ONCE(*execlists->csb_write, reset_value);
>  	wmb(); /* Make sure this is visible to HW (paranoia?) */
>  
> -	/*
> -	 * Sometimes Icelake forgets to reset its pointers on a GPU reset.
> -	 * Bludgeon them with a mmio update to be sure.
> -	 */
> +	invalidate_csb_entries(&execlists->csb_status[0],
> +			       &execlists->csb_status[reset_value]);
> +
> +	/* Once more for luck and our trusty paranoia */
>  	ENGINE_WRITE(engine, RING_CONTEXT_STATUS_PTR,
>  		     reset_value << 8 | reset_value);
>  	ENGINE_POSTING_READ(engine, RING_CONTEXT_STATUS_PTR);
>  
> -	invalidate_csb_entries(&execlists->csb_status[0],
> -			       &execlists->csb_status[reset_value]);
> +	GEM_BUG_ON(READ_ONCE(*execlists->csb_write) != reset_value);
>  }
>  
>  static void execlists_sanitize(struct intel_engine_cs *engine)
> -- 
> 2.20.1
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