[PATCH 1/2] drm/xe: Fix DSB buffer coherency

[Ville Syrjälä]

On Fri, Sep 13, 2024 at 01:47:53PM +0200, Maarten Lankhorst wrote:
> Add the scanout flag to force WC caching, and add the memory barrier
> where needed.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> ---
>  drivers/gpu/drm/xe/display/xe_dsb_buffer.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/display/xe_dsb_buffer.c b/drivers/gpu/drm/xe/display/xe_dsb_buffer.c
> index f99d901a3214f..f7949bf5426af 100644
> --- a/drivers/gpu/drm/xe/display/xe_dsb_buffer.c
> +++ b/drivers/gpu/drm/xe/display/xe_dsb_buffer.c
> @@ -48,11 +48,12 @@ bool intel_dsb_buffer_create(struct intel_crtc *crtc, struct intel_dsb_buffer *d
>  	if (!vma)
>  		return false;
>  
> +	/* Set scanout flag for WC mapping */
>  	obj = xe_bo_create_pin_map(xe, xe_device_get_root_tile(xe),
>  				   NULL, PAGE_ALIGN(size),
>  				   ttm_bo_type_kernel,
>  				   XE_BO_FLAG_VRAM_IF_DGFX(xe_device_get_root_tile(xe)) |
> -				   XE_BO_FLAG_GGTT);
> +				   XE_BO_FLAG_SCANOUT | XE_BO_FLAG_GGTT);
>  	if (IS_ERR(obj)) {
>  		kfree(vma);
>  		return false;
> @@ -73,5 +74,5 @@ void intel_dsb_buffer_cleanup(struct intel_dsb_buffer *dsb_buf)
>  
>  void intel_dsb_buffer_flush_map(struct intel_dsb_buffer *dsb_buf)
>  {
> -	/* TODO: add xe specific flush_map() for dsb buffer object. */
> +	xe_device_wmb(dsb_buf->vma->bo->tile->xe);

MMIO itself should be sufficient to flush the WC buffer.
But I guess no real harm in hammering it a bit harder.

>  }
> -- 
> 2.45.2

-- 
Ville Syrjälä
Intel