[Mesa-dev] [PATCH 4/4] radeonsi: clarify documentation of existing SI workaround

[Marek Olšák]

For the series:

Reviewed-by: Marek Olšák <marek.olsak at amd.com>

Marek

On Wed, May 3, 2017 at 3:58 PM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
> From: Nicolai Hähnle <nicolai.haehnle at amd.com>
>
> Limiting LS-HS to a single wave is required on all SI chips due to an
> issue with a power management feature.
> ---
>  src/gallium/drivers/radeonsi/si_state_draw.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/src/gallium/drivers/radeonsi/si_state_draw.c b/src/gallium/drivers/radeonsi/si_state_draw.c
> index 3d1d1f8..f31d5c2 100644
> --- a/src/gallium/drivers/radeonsi/si_state_draw.c
> +++ b/src/gallium/drivers/radeonsi/si_state_draw.c
> @@ -177,22 +177,24 @@ static void si_emit_derived_tess_state(struct si_context *sctx,
>         /* Make sure the output data fits in the offchip buffer */
>         *num_patches = MIN2(*num_patches,
>                             (sctx->screen->tess_offchip_block_dw_size * 4) /
>                             output_patch_size);
>
>         /* Not necessary for correctness, but improves performance. The
>          * specific value is taken from the proprietary driver.
>          */
>         *num_patches = MIN2(*num_patches, 40);
>
> -       /* SI bug workaround - limit LS-HS threadgroups to only one wave. */
>         if (sctx->b.chip_class == SI) {
> +               /* SI bug workaround, related to power management. Limit LS-HS
> +                * threadgroups to only one wave.
> +                */
>                 unsigned one_wave = 64 / MAX2(num_tcs_input_cp, num_tcs_output_cp);
>                 *num_patches = MIN2(*num_patches, one_wave);
>
>                 if (sctx->screen->b.info.max_se == 1) {
>                         /* The VGT HS block increments the patch ID unconditionally
>                          * within a single threadgroup. This results in incorrect
>                          * patch IDs when instanced draws are used.
>                          *
>                          * The intended solution is to restrict threadgroups to
>                          * a single instance by setting SWITCH_ON_EOI, which
> --
> 2.9.3
>
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