[Mesa-dev] [PATCH 02/12] i965/rbc: Set aux surface unconditionally for sampling engine

[Jason Ekstrand]

On Wed, Aug 31, 2016 at 8:17 AM, Topi Pohjolainen <
topi.pohjolainen at intel.com> wrote:

> Once mcs buffer gets allocated without delay for lossless
> compression (same as we do for msaa), one gets regression in:
>
> GL45-CTS.texture_barrier_ARB.same-texel-rw
>
> Setting the auxiliary surface for both sampling engine and data
> port seems to fix this. I haven't found any hardware documentation
> backing this though.
>
> Signed-off-by: Topi Pohjolainen <topi.pohjolainen at intel.com>
> ---
>  src/mesa/drivers/dri/i965/brw_wm_surface_state.c | 46
> ++++++++++++++++++++++--
>  1 file changed, 43 insertions(+), 3 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
> b/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
> index bfd973b..5cd27ef 100644
> --- a/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
> +++ b/src/mesa/drivers/dri/i965/brw_wm_surface_state.c
> @@ -72,6 +72,48 @@ static const struct surface_state_info
> surface_state_infos[] = {
>     [9] = {16, 64, 8,  10, SKL_MOCS_WB,  SKL_MOCS_PTE},
>  };
>
> +static bool
> +brw_needs_aux_surface(const struct brw_context *brw,
> +                      const struct intel_mipmap_tree *mt,
> +                      const struct isl_view *view)
> +{
> +   if (!mt->mcs_mt)
> +      return false;
> +
> +   if (view->usage & ISL_SURF_USAGE_RENDER_TARGET_BIT)
> +      return true;
> +
> +   const bool is_lossless_compressed =
> +      intel_miptree_is_lossless_compressed(brw, mt);
> +   const bool view_format_lossless_compressed =
> +       isl_format_supports_lossless_compression(brw->intelScreen->
> devinfo,
> +                                                view->format);
> +
> +   /* If the underlying surface is compressed but it is sampled using a
> +    * format that the sampling engine doesn't support as compressed, there
> +    * is no alternative but to treat the surface as non-compressed.
> +    */
>

Does this even work?  I mean, can you render to a texture with one format
and texture from it with another and still use color compression?


> +   if (is_lossless_compressed && !view_format_lossless_compressed) {
>

This is more of a change in behavior than the commit message says.  We
should probably make the commit message a bit better.


> +      /* Logic elsewhere needs to take care to resolve the color buffer
> prior
> +       * to sampling it as non-compressed.
> +       */
> +      assert(mt->fast_clear_state == INTEL_FAST_CLEAR_STATE_RESOLVED);
> +      return false;
> +   }
> +
> +   /* In practise it looks that setting the same lossless compressed
> surface
> +    * to be sampled without auxiliary surface and to be written with
> auxiliary
> +    * surface confuses the hardware.
> +    * Currently there is no direct way of knowing if render pass will use
> the
> +    * sane surface as render target and therefore simply use the auxiliary
> +    * surface unconditionally here.
> +    */
> +   if (is_lossless_compressed)
> +      return true;
>

This makes a lot of sense.  If we're sampling from and rendering to the
same surface, we'd better have the compression buffer for both.  That said,
if we ever bind a compressed buffer as a render target with a
texture-viewed version as a source (as per above), we're going to have a
problem...


> +
> +   return mt->fast_clear_state != INTEL_FAST_CLEAR_STATE_RESOLVED;
> +}
> +
>  static void
>  brw_emit_surface_state(struct brw_context *brw,
>                         struct intel_mipmap_tree *mt,
> @@ -135,9 +177,7 @@ brw_emit_surface_state(struct brw_context *brw,
>     struct isl_surf *aux_surf = NULL, aux_surf_s;
>     uint64_t aux_offset = 0;
>     enum isl_aux_usage aux_usage = ISL_AUX_USAGE_NONE;
> -   if (mt->mcs_mt &&
> -       ((view.usage & ISL_SURF_USAGE_RENDER_TARGET_BIT) ||
> -        mt->fast_clear_state != INTEL_FAST_CLEAR_STATE_RESOLVED)) {
> +   if (brw_needs_aux_surface(brw, mt, &view)) {
>        intel_miptree_get_aux_isl_surf(brw, mt, &aux_surf_s, &aux_usage);
>        aux_surf = &aux_surf_s;
>        assert(mt->mcs_mt->offset == 0);
> --
> 2.5.5
>
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