Re: [PATCH] drm/i915: Flush the WCB following a WC write

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

On Fri, Jul 06, 2018 at 12:54:02PM +0100, Chris Wilson wrote:
> If we have just completed a WC write, we must ensure that the WCB (Write
> Combining Buffer) is flushed out to main memory before we can expect to
> see the results. This is especially important when mixing WC with GTT as
> the physical paths are different and cachelines are not naturally flushed.
> 
> Testcase: igt/drv_selftests/live_coherency #gdg
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

> ---
>  drivers/gpu/drm/i915/i915_gem.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 0c0a1a959d0b..be63e8bbb6d2 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -837,6 +837,10 @@ flush_write_domain(struct drm_i915_gem_object *obj, unsigned int flush_domains)
>  		}
>  		break;
>  
> +	case I915_GEM_DOMAIN_WC:
> +		wmb();
> +		break;
> +
>  	case I915_GEM_DOMAIN_CPU:
>  		i915_gem_clflush_object(obj, I915_CLFLUSH_SYNC);
>  		break;
> -- 
> 2.18.0
> 
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