freedreno/a6xx: Document per-view viewport in GRAS_SU_CNTL

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20304>

src/freedreno/common/freedreno_dev_info.h

@@ -146,6 +146,12 @@ struct fd_dev_info {
          bool has_lrz_dir_tracking;
          bool lrz_track_quirk;
 
+         /* Some generations have a bit to add the multiview index to the
+          * viewport index, which lets us implement different scaling for
+          * different views.
+          */
+         bool has_per_view_viewport;
+
          struct {
             uint32_t PC_POWER_CNTL;
             uint32_t TPL1_DBG_ECO_CNTL;

src/freedreno/common/freedreno_devices.py

@@ -238,6 +238,7 @@ a6xx_gen3 = dict(
         has_lrz_dir_tracking = True,
         enable_lrz_fast_clear = True,
         lrz_track_quirk = True,
+        has_per_view_viewport = True,
     )
 
 # a635, a660:
@@ -263,6 +264,7 @@ a6xx_gen4 = dict(
         has_dp4acc = True,
         enable_lrz_fast_clear = True,
         has_lrz_dir_tracking = True,
+        has_per_view_viewport = True,
     )
 
 add_gpus([

src/freedreno/registers/adreno/a6xx.xml

@@ -1732,12 +1732,19 @@ to upconvert to 32b float internally?
 		<bitfield name="LINE_MODE" pos="13" type="a5xx_line_mode"/>
 		<bitfield name="UNK15" low="15" high="16"/>
 		<!--
-		This is set by the blob when multiview is enabled, but doesn't seem
-		to do anything.
+                        On gen1 only MULTIVIEW_ENABLE exists. On gen3 we have
+                        the ability to add the view index to either the RT array
+                        index or the viewport index, and it seems that
+                        MULTIVIEW_ENABLE doesn't do anything, instead we need to
+                        set at least one of RENDERTARGETINDEXINCR or
+                        VIEWPORTINDEXINCR to enable multiview. The blob still
+                        sets MULTIVIEW_ENABLE regardless.
+                        TODO: what about gen2 (a640)?
 		-->
-		<bitfield name="UNK17" pos="17" type="boolean"/>
-		<bitfield name="MULTIVIEW_ENABLE" pos="18" type="boolean"/>
-		<bitfield name="UNK19" low="19" high="22"/>
+		<bitfield name="MULTIVIEW_ENABLE" pos="17" type="boolean"/>
+		<bitfield name="RENDERTARGETINDEXINCR" pos="18" type="boolean"/>
+		<bitfield name="VIEWPORTINDEXINCR" pos="19" type="boolean"/>
+		<bitfield name="UNK20" low="20" high="22"/>
 	</reg32>
 	<reg32 offset="0x8091" name="GRAS_SU_POINT_MINMAX">
 		<bitfield name="MIN" low="0" high="15" type="ufixed" radix="4"/>

src/freedreno/vulkan/tu_pipeline.cc

@@ -2205,8 +2205,8 @@ tu6_gras_su_cntl(const VkPipelineRasterizationStateCreateInfo *rast_info,
 
    if (multiview) {
       gras_su_cntl |=
-         A6XX_GRAS_SU_CNTL_UNK17 |
-         A6XX_GRAS_SU_CNTL_MULTIVIEW_ENABLE;
+         A6XX_GRAS_SU_CNTL_MULTIVIEW_ENABLE |
+         A6XX_GRAS_SU_CNTL_RENDERTARGETINDEXINCR;
    }
 
    return gras_su_cntl;