etnaviv: Support PIPE_QUERY_PRIMITIVES_EMITTED

Add support for transform feedback primitive counting queries using the
hardware TFB query mechanism. The implementation uses dedicated query
registers (VIVS_TFB_QUERY_BUFFER and VIVS_TFB_QUERY_COMMAND) to track
the number of primitives written during transform feedback operations.

The hardware automatically accumulates primitive counts and stores the
final result at offset 0 of the query buffer, eliminating the need for
manual accumulation.

Signed-off-by: Christian Gmeiner <cgmeiner@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37320>

src/gallium/drivers/etnaviv/etnaviv_query_acc.c

@@ -38,11 +38,13 @@
 
 extern const struct etna_acc_sample_provider occlusion_provider;
 extern const struct etna_acc_sample_provider perfmon_provider;
+extern const struct etna_acc_sample_provider xfb_provider;
 
 static const struct etna_acc_sample_provider *acc_sample_provider[] =
 {
    &occlusion_provider,
    &perfmon_provider,
+   &xfb_provider,
 };
 
 static void

src/gallium/drivers/etnaviv/etnaviv_query_acc_xfb.c

@@ -0,0 +1,71 @@
+/*
+ * Copyright © 2025 Igalia S.L.
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "hw/state_3d.xml.h"
+#include "etnaviv_context.h"
+#include "etnaviv_emit.h"
+#include "etnaviv_query_acc.h"
+
+static bool
+xfb_supports(struct etna_context *ctx, unsigned query_type)
+{
+   if (!VIV_FEATURE(ctx->screen, ETNA_FEATURE_HWTFB))
+      return false;
+
+   switch (query_type) {
+   case PIPE_QUERY_PRIMITIVES_EMITTED:
+      return true;
+   default:
+      return false;
+   }
+}
+
+static struct etna_acc_query *
+xfb_allocate(UNUSED struct etna_context *ctx, UNUSED unsigned query_type)
+{
+   return CALLOC_STRUCT(etna_acc_query);
+}
+
+static void
+xfb_resume(struct etna_acc_query *aq, struct etna_context *ctx)
+{
+   struct etna_buffer_resource *rsc = etna_buffer_resource(aq->prsc);
+   struct etna_reloc r = {
+      .bo = rsc->bo,
+      .flags = ETNA_RELOC_WRITE
+   };
+
+   etna_set_state_reloc(ctx->stream, VIVS_TFB_QUERY_BUFFER, &r);
+   etna_set_state(ctx->stream, VIVS_TFB_QUERY_COMMAND, TFB_QUERY_COMMAND_ENABLE);
+   resource_written(ctx, aq->prsc);
+}
+
+static void
+xfb_suspend(struct etna_acc_query *aq, struct etna_context *ctx)
+{
+   etna_set_state(ctx->stream, VIVS_TFB_QUERY_COMMAND, TFB_QUERY_COMMAND_DISABLE);
+   etna_set_state(ctx->stream, VIVS_TFB_FLUSH, 0x1);
+   resource_written(ctx, aq->prsc);
+}
+
+static bool
+xfb_result(UNUSED struct etna_acc_query *aq, void *buf,
+           union pipe_query_result *result)
+{
+   /* The GPU stores the final results at offset 0 - no need
+    * to do any manual accumulation.
+    */
+   result->u64 = *(uint64_t *)buf;
+
+   return true;
+}
+
+const struct etna_acc_sample_provider xfb_provider = {
+   .supports = xfb_supports,
+   .allocate = xfb_allocate,
+   .suspend = xfb_suspend,
+   .resume = xfb_resume,
+   .result = xfb_result,
+};

src/gallium/drivers/etnaviv/meson.build

@@ -51,6 +51,7 @@ files_etnaviv = files(
   'etnaviv_query.h',
   'etnaviv_query_acc_occlusion.c',
   'etnaviv_query_acc_perfmon.c',
+  'etnaviv_query_acc_xfb.c',
   'etnaviv_query_acc.c',
   'etnaviv_query_acc.h',
   'etnaviv_query_sw.c',