[PATCH v2] drm/xe: Use ttm_uncached for BO with NEEDS_UC flag

[Matt Roper]

On Tue, Jun 18, 2024 at 12:49:47PM +0200, Michal Wajdeczko wrote:
> We should honor requested uncached mode also at the TTM layer.
> Otherwise, we risk losing updates to the memory based interrupts
> source or status vectors, as those require uncached memory.
> 
> Signed-off-by: Michal Wajdeczko <michal.wajdeczko at intel.com>
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: Matt Roper <matthew.d.roper at intel.com>
> ---
> v2: assert that cpu_caching is unset (Matt)

Reviewed-by: Matt Roper <matthew.d.roper at intel.com>

> ---
>  drivers/gpu/drm/xe/xe_bo.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index 74294f1b05bc..65c696966e96 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -378,6 +378,15 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo,
>  	    (xe->info.graphics_verx100 >= 1270 && bo->flags & XE_BO_FLAG_PAGETABLE))
>  		caching = ttm_write_combined;
>  
> +	if (bo->flags & XE_BO_FLAG_NEEDS_UC) {
> +		/*
> +		 * Valid only for internally-created buffers only, for
> +		 * which cpu_caching is never initialized.
> +		 */
> +		xe_assert(xe, bo->cpu_caching == 0);
> +		caching = ttm_uncached;
> +	}
> +
>  	err = ttm_tt_init(&tt->ttm, &bo->ttm, page_flags, caching, extra_pages);
>  	if (err) {
>  		kfree(tt);
> -- 
> 2.43.0
> 

-- 
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation