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-rw-r--r--src/intel/compiler/brw_fs_generator.cpp1
-rw-r--r--src/mesa/drivers/dri/i965/intel_extensions.c25
2 files changed, 25 insertions, 1 deletions
diff --git a/src/intel/compiler/brw_fs_generator.cpp b/src/intel/compiler/brw_fs_generator.cpp
index 649dd999a0e..c24d4eb7cab 100644
--- a/src/intel/compiler/brw_fs_generator.cpp
+++ b/src/intel/compiler/brw_fs_generator.cpp
@@ -2100,6 +2100,7 @@ fs_generator::generate_code(const cfg_t *cfg, int dispatch_width)
break;
case SHADER_OPCODE_INTERLOCK:
+ assert(devinfo->gen >= 9);
/* The interlock is basically a memory fence issued via sendc */
brw_memory_fence(p, dst, BRW_OPCODE_SENDC);
break;
diff --git a/src/mesa/drivers/dri/i965/intel_extensions.c b/src/mesa/drivers/dri/i965/intel_extensions.c
index d7080fb21b4..afca881e5d9 100644
--- a/src/mesa/drivers/dri/i965/intel_extensions.c
+++ b/src/mesa/drivers/dri/i965/intel_extensions.c
@@ -254,7 +254,6 @@ intelInitExtensions(struct gl_context *ctx)
ctx->Extensions.EXT_shader_samples_identical = true;
ctx->Extensions.OES_primitive_bounding_box = true;
ctx->Extensions.OES_texture_buffer = true;
- ctx->Extensions.ARB_fragment_shader_interlock = true;
if (can_do_pipelined_register_writes(brw->screen)) {
ctx->Extensions.ARB_draw_indirect = true;
@@ -327,6 +326,30 @@ intelInitExtensions(struct gl_context *ctx)
ctx->Extensions.KHR_blend_equation_advanced_coherent = true;
ctx->Extensions.KHR_texture_compression_astc_ldr = true;
ctx->Extensions.KHR_texture_compression_astc_sliced_3d = true;
+
+ /*
+ * From the Skylake PRM Vol. 7 (Memory Fence Message, page 221):
+ * "A memory fence message issued by a thread causes further messages
+ * issued by the thread to be blocked until all previous data port
+ * messages have completed, or the results can be globally observed from
+ * the point of view of other threads in the system."
+ *
+ * From the Haswell PRM Vol. 7 (Memory Fence, page 256):
+ * "A memory fence message issued by a thread causes further messages
+ * issued by the thread to be blocked until all previous messages issued
+ * by the thread to that data port (data cache or render cache) have
+ * been globally observed from the point of view of other threads in the
+ * system."
+ *
+ * Summarized: For ARB_fragment_shader_interlock to work, we need to
+ * ensure memory access ordering for all messages to the dataport from
+ * all threads. Memory fence messages prior to SKL only provide memory
+ * access ordering for messages from the same thread, so we can only
+ * support the feature from Gen9 onwards.
+ *
+ */
+
+ ctx->Extensions.ARB_fragment_shader_interlock = true;
}
if (gen_device_info_is_9lp(devinfo))