[Mesa-dev] [PATCH] i965/skl/gt4: Fix URB programming restriction.

[Kenneth Graunke]

On Friday, November 06, 2015 06:12:27 PM Ben Widawsky wrote:
> The comment in the code details the restriction. Thanks to Ken for having a very
> helpful conversation with me, and spotting the blurb in the link I sent him :P.
> 
> There are still stability problems for me on GT4, but this definitely helps with
> some of the failures.
> 
> Cc: Kenneth Graunke <kenneth at whitecape.org>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: mesa-stable at lists.freedesktop.org (if the original gt4 patch goes to stable)
> ---
> 
> Sarah, you should check this on KBL.
> Cc: Sarah Sharp <sarah.a.sharp at linux.intel.com>
> ---
>  src/mesa/drivers/dri/i965/brw_device_info.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_device_info.c b/src/mesa/drivers/dri/i965/brw_device_info.c
> index 2ebc084..6117fd3 100644
> --- a/src/mesa/drivers/dri/i965/brw_device_info.c
> +++ b/src/mesa/drivers/dri/i965/brw_device_info.c
> @@ -337,6 +337,14 @@ static const struct brw_device_info brw_device_info_skl_gt3 = {
>  
>  static const struct brw_device_info brw_device_info_skl_gt4 = {
>     GEN9_FEATURES, .gt = 4,
> +   /* From the docs:
> +    *   URB is limited to 1008KB due to programming restrictions. This is not a
> +    *   restriction of the L3 implementation, but of the FF and other clients.
> +    *   Therefore, in a GT4 implementation it is possible for the programmed
> +    *   allocation of the L3 data array to provide 3*384KB=1152MB [sic] for URB,
> +    *   but only 1008KB of this will be used.
> +    */

We should at least say which page/section this comes from (the section
name exists in the Broadwell PRM, so it's not particularly secret).

Please put the text in quotes too.  My suggested formatting:

   /* From the "L3 Allocation and Programming" documentation:
    *
    * "URB is limited to 1008KB due to programming restrictions.  This
    *  is not a restriction of the L3 implementation, but of the FF and
    *  other clients.  Therefore, in a GT4 implementation it is
    *  possible for the programmed allocation of the L3 data array to
    *  provide 3*384KB=1152MB [sic] for URB, but only 1008KB of this
    *  will be used."
    */

Regardless,
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

> +   .urb.size = 1008 / 3,
>  };
>  
>  static const struct brw_device_info brw_device_info_bxt = {
> 
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