comp: Add setting to force a vulkan gpu index

src/xrt/compositor/common/comp_vk.c

@@ -825,7 +825,7 @@ vk_get_device_functions(struct vk_bundle *vk)
  */
 
 static VkResult
-vk_select_physical_device(struct vk_bundle *vk)
+vk_select_physical_device(struct vk_bundle *vk, int forced_index)
 {
 	VkPhysicalDevice physical_devices[16];
 	uint32_t gpu_count = ARRAY_SIZE(physical_devices);
@@ -848,14 +848,23 @@ vk_select_physical_device(struct vk_bundle *vk)
 		VK_DEBUG(vk, "Can not deal well with multiple devices.");
 	}
 
-	// as a first-step to 'intelligent' selection, prefer a 'discrete' gpu
-	// if it is present
+	VK_DEBUG(vk, "Choosing Vulkan device index");
 	uint32_t gpu_index = 0;
-	for (uint32_t i = 0; i < gpu_count; i++) {
-		VkPhysicalDeviceProperties pdp;
-		vk->vkGetPhysicalDeviceProperties(physical_devices[i], &pdp);
-		if (pdp.deviceType == VK_PHYSICAL_DEVICE_TYPE_DISCRETE_GPU) {
-			gpu_index = i;
+	if (forced_index > -1) {
+		gpu_index = forced_index;
+		VK_DEBUG(vk, "Forced use of Vulkan device index %d.",
+		         gpu_index);
+	} else {
+		// as a first-step to 'intelligent' selection, prefer a
+		// 'discrete' gpu if it is present
+		for (uint32_t i = 0; i < gpu_count; i++) {
+			VkPhysicalDeviceProperties pdp;
+			vk->vkGetPhysicalDeviceProperties(physical_devices[i],
+			                                  &pdp);
+			if (pdp.deviceType ==
+			    VK_PHYSICAL_DEVICE_TYPE_DISCRETE_GPU) {
+				gpu_index = i;
+			}
 		}
 	}
 
@@ -929,11 +938,11 @@ err_free:
 }
 
 VkResult
-vk_create_device(struct vk_bundle *vk)
+vk_create_device(struct vk_bundle *vk, int forced_index)
 {
 	VkResult ret;
 
-	ret = vk_select_physical_device(vk);
+	ret = vk_select_physical_device(vk, forced_index);
 	if (ret != VK_SUCCESS) {
 		return ret;
 	}

src/xrt/compositor/common/comp_vk.h

@@ -253,7 +253,7 @@ vk_init_cmd_pool(struct vk_bundle *vk);
  * @ingroup comp_common
  */
 VkResult
-vk_create_device(struct vk_bundle *vk);
+vk_create_device(struct vk_bundle *vk, int forced_index);
 
 /*!
  * Initialize a bundle with objects given to us by client code,

src/xrt/compositor/main/comp_compositor.c

@@ -442,7 +442,7 @@ compositor_init_vulkan(struct comp_compositor *c)
 		return false;
 	}
 
-	ret = vk_create_device(&c->vk);
+	ret = vk_create_device(&c->vk, c->settings.gpu_index);
 	if (ret != VK_SUCCESS) {
 		return false;
 	}
@@ -531,7 +531,7 @@ compositor_check_vulkan_caps(struct comp_compositor *c)
 	}
 
 	// follow same device selection logic as subsequent calls
-	ret = vk_create_device(&temp_vk);
+	ret = vk_create_device(&temp_vk, c->settings.gpu_index);
 	if (ret != VK_SUCCESS) {
 		COMP_ERROR(c, "Failed to create VkDevice: %s",
 		           vk_result_string(ret));

src/xrt/compositor/main/comp_settings.c

@@ -18,6 +18,7 @@ DEBUG_GET_ONCE_BOOL_OPTION(force_nvidia, "XRT_COMPOSITOR_FORCE_NVIDIA", false)
 DEBUG_GET_ONCE_BOOL_OPTION(force_xcb, "XRT_COMPOSITOR_FORCE_XCB", false)
 DEBUG_GET_ONCE_BOOL_OPTION(force_wayland, "XRT_COMPOSITOR_FORCE_WAYLAND", false)
 DEBUG_GET_ONCE_BOOL_OPTION(validate_vulkan, "XRT_COMPOSITOR_VULKAN_VALIDATION", false)
+DEBUG_GET_ONCE_NUM_OPTION(force_gpu_index, "XRT_COMPOSITOR_FORCE_GPU_INDEX", -1)
 // clang-format on
 
 void
@@ -43,6 +44,7 @@ comp_settings_init(struct comp_settings *s, struct xrt_device *xdev)
 	s->print_spew = debug_get_bool_option_print_spew();
 	s->print_debug = debug_get_bool_option_print_debug();
 	s->validate_vulkan = debug_get_bool_option_validate_vulkan();
+	s->gpu_index = debug_get_num_option_force_gpu_index();
 
 	if (debug_get_bool_option_force_nvidia()) {
 		s->window_type = WINDOW_DIRECT_NVIDIA;

src/xrt/compositor/main/comp_settings.h

@@ -84,6 +84,9 @@ struct comp_settings
 
 	//! Enable vulkan validation for compositor
 	bool validate_vulkan;
+
+	//! Run the compositor on this Vulkan physical device
+	int gpu_index;
 };
 
 /*!