[Mesa-dev] [PATCH 4/4] i965: Fix the SF Vertex URB Read Length calculation for Gen7 platforms.

[Paul Berry]

On 2 February 2013 13:52, Kenneth Graunke <kenneth at whitecape.org> wrote:

> Ivybridge doesn't appear to have the same errata as Sandybridge; no
> corruption was observed by setting it to more than the minimal correct
> value.  It's possible that we were simply lucky, since the URB entries
> are 1024-bit on Ivybridge vs. 512-bit Sandybridge.  Or perhaps the
> underlying hardware issue is fixed.
>
> Either way, we may as well program the minimum value since it's now
> readily available, likely to be more efficient, and possibly more
> correct.
>
> NOTE: This is a candidate for all stable branches.
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> ---
>  src/mesa/drivers/dri/i965/gen7_sf_state.c | 32
> +++++++++++++++----------------
>  1 file changed, 16 insertions(+), 16 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/gen7_sf_state.c
> b/src/mesa/drivers/dri/i965/gen7_sf_state.c
> index b801b96..f7ad473 100644
> --- a/src/mesa/drivers/dri/i965/gen7_sf_state.c
> +++ b/src/mesa/drivers/dri/i965/gen7_sf_state.c
> @@ -34,7 +34,6 @@ upload_sbe_state(struct brw_context *brw)
>  {
>     struct intel_context *intel = &brw->intel;
>     struct gl_context *ctx = &intel->ctx;
> -   uint32_t urb_entry_read_length;
>     /* BRW_NEW_FRAGMENT_PROGRAM */
>     uint32_t num_outputs =
> _mesa_bitcount_64(brw->fragment_program->Base.InputsRead);
>     /* _NEW_LIGHT */
> @@ -48,22 +47,8 @@ upload_sbe_state(struct brw_context *brw)
>     bool render_to_fbo = _mesa_is_user_fbo(ctx->DrawBuffer);
>     uint32_t point_sprite_origin;
>
> -   /* CACHE_NEW_VS_PROG */
> -   urb_entry_read_length = ((brw->vs.prog_data->vue_map.num_slots + 1) /
> 2 -
> -                           urb_entry_read_offset);
> -   if (urb_entry_read_length == 0) {
> -      /* Setting the URB entry read length to 0 causes undefined
> behavior, so
> -       * if we have no URB data to read, set it to 1.
> -       */
> -      urb_entry_read_length = 1;
> -   }
> -
>     /* FINISHME: Attribute Swizzle Control Mode? */
> -   dw1 =
> -      GEN7_SBE_SWIZZLE_ENABLE |
> -      num_outputs << GEN7_SBE_NUM_OUTPUTS_SHIFT |
> -      urb_entry_read_length << GEN7_SBE_URB_ENTRY_READ_LENGTH_SHIFT |
> -      urb_entry_read_offset << GEN7_SBE_URB_ENTRY_READ_OFFSET_SHIFT;
> +   dw1 = GEN7_SBE_SWIZZLE_ENABLE | num_outputs <<
> GEN7_SBE_NUM_OUTPUTS_SHIFT;
>
>     /* _NEW_POINT
>      *
> @@ -123,6 +108,21 @@ upload_sbe_state(struct brw_context *brw)
>                             &max_source_attr);
>     }
>
> +   /* From the Ivy Bridge PRM, Volume 2, Part 1, documentation for
> +    * 3DSTATE_SBE DWord 1 bits 15:11, "Vertex URB Entry Read Length":
> +    *
> +    * "This field should be set to the minimum length required to read the
> +    *  maximum source attribute.  The maximum source attribute is
> indicated
> +    *  by the maximum value of the enabled Attribute # Source Attribute if
> +    *  Attribute Swizzle Enable is set, Number of Output Attributes-1 if
> +    *  enable is not set.
> +    *
> +    *  read_length = ceiling((max_source_attr + 1) / 2)"
> +    */
> +   uint32_t urb_entry_read_length = ALIGN(max_source_attr + 1, 2) / 2;
> +   dw1 |= urb_entry_read_length << GEN6_SF_URB_ENTRY_READ_LENGTH_SHIFT |
> +          urb_entry_read_offset << GEN6_SF_URB_ENTRY_READ_OFFSET_SHIFT;
> +
>

s/GEN6_SF/GEN7_SBE/ above.

(Fortunately these #defines are the same for GEN6 and GEN7 but it would be
nice to use the right ones :))

With that fixed, this series is:

Reviewed-by: Paul Berry <stereotype441 at gmail.com>


>     for (; input_index < FRAG_ATTRIB_MAX; input_index++)
>        attr_overrides[input_index] = 0;
>
> --
> 1.8.1.2
>
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