[Mesa-dev] [PATCH V2 11/12] i965/gen7: Enable the features required for GL_ARB_sample_shading

[Anuj Phogat]

- Enable GEN7_WM_MSDISPMODE_PERSAMPLE, GEN7_WM_POSOFFSET_SAMPLE,
  GEN7_WM_OMASK_TO_RENDER_TARGET as per extension's specification.
- Only enable one of GEN7_WM_8_DISPATCH_ENABLE or GEN7_WM_16_DISPATCH_ENABLE
  when GEN7_WM_MSDISPMODE_PERSAMPLE is enabled. Refer IVB PRM Vol. 2, Part 1,
  Page 288 for details.

V2: - Add a comment explaining why only SIMD8 mode is enabled with
      MSDISPMODE_PERSAMPLE.
    - Use shared function _mesa_get_min_invocations_per_fragment().
    - Use brw_wm_prog_data variables: uses_pos_offset, uses_omask.
Signed-off-by: Anuj Phogat <anuj.phogat at gmail.com>
---
 src/mesa/drivers/dri/i965/gen7_wm_state.c | 53 +++++++++++++++++++++++++++++--
 1 file changed, 50 insertions(+), 3 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/gen7_wm_state.c b/src/mesa/drivers/dri/i965/gen7_wm_state.c
index a2046c3..493b107 100644
--- a/src/mesa/drivers/dri/i965/gen7_wm_state.c
+++ b/src/mesa/drivers/dri/i965/gen7_wm_state.c
@@ -27,6 +27,7 @@
 #include "brw_defines.h"
 #include "brw_util.h"
 #include "brw_wm.h"
+#include "program/program.h"
 #include "program/prog_parameter.h"
 #include "program/prog_statevars.h"
 #include "intel_batchbuffer.h"
@@ -82,9 +83,13 @@ upload_wm_state(struct brw_context *brw)
       GEN7_WM_BARYCENTRIC_INTERPOLATION_MODE_SHIFT;
 
    /* _NEW_COLOR, _NEW_MULTISAMPLE */
+   /* Enable if the pixel shader kernel generates and outputs oMask.
+    */
    if (fp->program.UsesKill || ctx->Color.AlphaEnabled ||
-       ctx->Multisample.SampleAlphaToCoverage)
+       ctx->Multisample.SampleAlphaToCoverage ||
+       brw->wm.prog_data->uses_omask) {
       dw1 |= GEN7_WM_KILL_ENABLE;
+   }
 
    /* _NEW_BUFFERS */
    if (brw_color_buffer_write_enabled(brw) || writes_depth ||
@@ -97,7 +102,11 @@ upload_wm_state(struct brw_context *brw)
          dw1 |= GEN7_WM_MSRAST_ON_PATTERN;
       else
          dw1 |= GEN7_WM_MSRAST_OFF_PIXEL;
-      dw2 |= GEN7_WM_MSDISPMODE_PERPIXEL;
+
+      if (_mesa_get_min_invocations_per_fragment(ctx, brw->fragment_program) > 1)
+         dw2 |= GEN7_WM_MSDISPMODE_PERSAMPLE;
+      else
+         dw2 |= GEN7_WM_MSDISPMODE_PERPIXEL;
    } else {
       dw1 |= GEN7_WM_MSRAST_OFF_PIXEL;
       dw2 |= GEN7_WM_MSDISPMODE_PERSAMPLE;
@@ -169,6 +178,32 @@ upload_ps_state(struct brw_context *brw)
    if (brw->wm.prog_data->nr_params > 0)
       dw4 |= GEN7_PS_PUSH_CONSTANT_ENABLE;
 
+   /* From the IVB PRM, volume 2 part 1, page 287:
+    * "This bit is inserted in the PS payload header and made available to
+    * the DataPort (either via the message header or via header bypass) to
+    * indicate that oMask data (one or two phases) is included in Render
+    * Target Write messages. If present, the oMask data is used to mask off
+    * samples."
+    */
+   if (brw->wm.prog_data->uses_omask)
+      dw4 |= GEN7_PS_OMASK_TO_RENDER_TARGET;
+
+   /* From the IVB PRM, volume 2 part 1, page 287:
+    * "If the PS kernel does not need the Position XY Offsets to
+    * compute a Position Value, then this field should be programmed
+    * to POSOFFSET_NONE."
+    * "SW Recommendation: If the PS kernel needs the Position Offsets
+    * to compute a Position XY value, this field should match Position
+    * ZW Interpolation Mode to ensure a consistent position.xyzw
+    * computation."
+    * We only require XY sample offsets. So, this recommendation doesn't
+    * look useful at the moment. We might need this in future.
+    */
+   if (brw->wm.prog_data->uses_pos_offset)
+      dw4 |= GEN7_PS_POSOFFSET_SAMPLE;
+   else
+      dw4 |= GEN7_PS_POSOFFSET_NONE;
+
    /* CACHE_NEW_WM_PROG | _NEW_COLOR
     *
     * The hardware wedges if you have this bit set but don't turn on any dual
@@ -184,8 +219,20 @@ upload_ps_state(struct brw_context *brw)
    if (brw->wm.prog_data->num_varying_inputs != 0)
       dw4 |= GEN7_PS_ATTRIBUTE_ENABLE;
 
+   /* In case of non 1x (i.e 4x, 8x) multisampling with MSDISPMODE_PERSAMPLE,
+    * only one of SIMD8 and SIMD16 should be enabled. So, we have two options
+    * in that case:
+    * 'SIMD8 only' dispatch:   allowed on gen7.
+    * 'SIMD16 only' dispatch:  allowed on gen7 except when in PERSAMPLE mode
+    *                          with number of multisamples >= 8.
+    * TODO: Currently we enable 'SIMD8 only' dispatch in above mentioned case.
+    *       Make changes to allow 'SIMD16 only' dispatch for multisamples < 8.
+    */
    dw4 |= GEN7_PS_8_DISPATCH_ENABLE;
-   if (brw->wm.prog_data->prog_offset_16)
+
+   if (brw->wm.prog_data->prog_offset_16 &&
+       !(_mesa_get_min_invocations_per_fragment(ctx,
+                                                brw->fragment_program ) > 1))
       dw4 |= GEN7_PS_16_DISPATCH_ENABLE;
 
    dw5 |= (brw->wm.prog_data->first_curbe_grf <<
-- 
1.8.1.4