anv: Submit a dummy batch when only semaphores are provided.

Vulkan allows you to do a submit whose only job is to wait on and
trigger semaphores.  The easiest way for us to support that right
now is to insert a dummy execbuf.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

src/intel/vulkan/anv_batch_chain.c

@@ -1388,6 +1388,23 @@ setup_execbuf_for_cmd_buffer(struct anv_execbuf *execbuf,
    return VK_SUCCESS;
 }
 
+static void
+setup_empty_execbuf(struct anv_execbuf *execbuf, struct anv_device *device)
+{
+   anv_execbuf_add_bo(execbuf, &device->trivial_batch_bo, NULL, 0,
+                      &device->alloc);
+
+   execbuf->execbuf = (struct drm_i915_gem_execbuffer2) {
+      .buffers_ptr = (uintptr_t) execbuf->objects,
+      .buffer_count = execbuf->bo_count,
+      .batch_start_offset = 0,
+      .batch_len = 8, /* GEN7_MI_BATCH_BUFFER_END and NOOP */
+      .flags = I915_EXEC_HANDLE_LUT | I915_EXEC_RENDER,
+      .rsvd1 = device->context_id,
+      .rsvd2 = 0,
+   };
+}
+
 VkResult
 anv_cmd_buffer_execbuf(struct anv_device *device,
                        struct anv_cmd_buffer *cmd_buffer,
@@ -1448,9 +1465,14 @@ anv_cmd_buffer_execbuf(struct anv_device *device,
       }
    }
 
-   result = setup_execbuf_for_cmd_buffer(&execbuf, cmd_buffer);
-   if (result != VK_SUCCESS)
-      return result;
+   if (cmd_buffer) {
+      result = setup_execbuf_for_cmd_buffer(&execbuf, cmd_buffer);
+      if (result != VK_SUCCESS)
+         return result;
+   } else {
+      setup_empty_execbuf(&execbuf, device);
+   }
+
 
    result = anv_device_execbuf(device, &execbuf.execbuf, execbuf.bos);
 

src/intel/vulkan/anv_device.c

@@ -1014,6 +1014,32 @@ anv_device_init_border_colors(struct anv_device *device)
                                                     border_colors);
 }
 
+static void
+anv_device_init_trivial_batch(struct anv_device *device)
+{
+   anv_bo_init_new(&device->trivial_batch_bo, device, 4096);
+
+   if (device->instance->physicalDevice.has_exec_async)
+      device->trivial_batch_bo.flags |= EXEC_OBJECT_ASYNC;
+
+   void *map = anv_gem_mmap(device, device->trivial_batch_bo.gem_handle,
+                            0, 4096, 0);
+
+   struct anv_batch batch = {
+      .start = map,
+      .next = map,
+      .end = map + 4096,
+   };
+
+   anv_batch_emit(&batch, GEN7_MI_BATCH_BUFFER_END, bbe);
+   anv_batch_emit(&batch, GEN7_MI_NOOP, noop);
+
+   if (!device->info.has_llc)
+      gen_clflush_range(map, batch.next - map);
+
+   anv_gem_munmap(map, device->trivial_batch_bo.size);
+}
+
 VkResult anv_CreateDevice(
     VkPhysicalDevice                            physicalDevice,
     const VkDeviceCreateInfo*                   pCreateInfo,
@@ -1131,6 +1157,8 @@ VkResult anv_CreateDevice(
    if (result != VK_SUCCESS)
       goto fail_surface_state_pool;
 
+   anv_device_init_trivial_batch(device);
+
    anv_scratch_pool_init(device, &device->scratch_pool);
 
    anv_queue_init(device, &device->queue);
@@ -1220,6 +1248,8 @@ void anv_DestroyDevice(
    anv_gem_munmap(device->workaround_bo.map, device->workaround_bo.size);
    anv_gem_close(device, device->workaround_bo.gem_handle);
 
+   anv_gem_close(device, device->trivial_batch_bo.gem_handle);
+
    anv_state_pool_finish(&device->surface_state_pool);
    anv_state_pool_finish(&device->instruction_state_pool);
    anv_state_pool_finish(&device->dynamic_state_pool);

src/intel/vulkan/anv_private.h

@@ -745,6 +745,7 @@ struct anv_device {
     struct anv_state_pool                       surface_state_pool;
 
     struct anv_bo                               workaround_bo;
+    struct anv_bo                               trivial_batch_bo;
 
     struct anv_pipeline_cache                   blorp_shader_cache;
     struct blorp_context                        blorp;

src/intel/vulkan/anv_queue.c

@@ -159,6 +159,23 @@ VkResult anv_QueueSubmit(
    pthread_mutex_lock(&device->mutex);
 
    for (uint32_t i = 0; i < submitCount; i++) {
+      if (pSubmits[i].commandBufferCount == 0) {
+         /* If we don't have any command buffers, we need to submit a dummy
+          * batch to give GEM something to wait on.  We could, potentially,
+          * come up with something more efficient but this shouldn't be a
+          * common case.
+          */
+         result = anv_cmd_buffer_execbuf(device, NULL,
+                                         pSubmits[i].pWaitSemaphores,
+                                         pSubmits[i].waitSemaphoreCount,
+                                         pSubmits[i].pSignalSemaphores,
+                                         pSubmits[i].signalSemaphoreCount);
+         if (result != VK_SUCCESS)
+            goto out;
+
+         continue;
+      }
+
       for (uint32_t j = 0; j < pSubmits[i].commandBufferCount; j++) {
          ANV_FROM_HANDLE(anv_cmd_buffer, cmd_buffer,
                          pSubmits[i].pCommandBuffers[j]);