Re: [PATCH] drm/i915: Flush the CSB pointer reset

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

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

> The HW resets it CSB tail pointer on resetting the engine. Most of the
> time. In case it doesn't (and for system resume) we write the expected
> value anyway. For extra paranoia, flush the write before we invalidate
> the cacheline.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_lrc.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 3cb788a223ef..4e0a351bfbca 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1866,6 +1866,7 @@ static void reset_csb_pointers(struct intel_engine_execlists *execlists)
>  	 */
>  	execlists->csb_head = reset_value;
>  	WRITE_ONCE(*execlists->csb_write, reset_value);
> +	wmb(); /* Make sure this is visible to HW (paranoia?) */

As alternative tho, how about we invalidate not only the csb portion
but the all things included in hswp. Then read the the mmio tail/head,
assert they are pointing correctly and match hwsp, if not, correct
and log?

-Mika

>  
>  	invalidate_csb_entries(&execlists->csb_status[0],
>  			       &execlists->csb_status[reset_value]);
> -- 
> 2.20.1
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