[Intel-xe] [PATCH 2/7] drm/xe: Fix comment on Wa_22013088509

[Rodrigo Vivi]

On Thu, May 04, 2023 at 12:32:45AM -0700, Lucas De Marchi wrote:
> On i915 the "see comment about Wa_22013088509" referred to the comment
> in the graphics version >= 11 branch, where there were more details
> about it. From the platforms supported by xe, only PVC needs
> Wa_22013088509, but as the comment says, it's simpler to do it for all
> platforms as there is no downside.  Bring the missing comment over from
> i915 and reword it to fit xe better.
> 
> Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>

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

> ---
>  drivers/gpu/drm/xe/xe_gt_mcr.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_gt_mcr.c b/drivers/gpu/drm/xe/xe_gt_mcr.c
> index 55b240a5eaa7..02afb313bfea 100644
> --- a/drivers/gpu/drm/xe/xe_gt_mcr.c
> +++ b/drivers/gpu/drm/xe/xe_gt_mcr.c
> @@ -461,9 +461,16 @@ static u32 rw_with_mcr_steering(struct xe_gt *gt, struct xe_reg_mcr reg_mcr,
>  	}
>  
>  	/*
> -	 * Always leave the hardware in multicast mode when doing reads
> -	 * (see comment about Wa_22013088509 below) and only change it
> -	 * to unicast mode when doing writes of a specific instance.
> +	 * Always leave the hardware in multicast mode when doing reads and only
> +	 * change it to unicast mode when doing writes of a specific instance.
> +	 *
> +	 * The setting of the multicast/unicast bit usually wouldn't matter for
> +	 * read operations (which always return the value from a single register
> +	 * instance regardless of how that bit is set), but some platforms may
> +	 * have workarounds requiring us to remain in multicast mode for reads,
> +	 * e.g. Wa_22013088509 on PVC.  There's no real downside to this, so
> +	 * we'll just go ahead and do so on all platforms; we'll only clear the
> +	 * multicast bit from the mask when explicitly doing a write operation.
>  	 *
>  	 * No need to save old steering reg value.
>  	 */
> -- 
> 2.40.1
>