drm-shim: Let the driver choose to overwrite the first render node.

When I was writing drm-shim, I was focused on the v3d kmsro case -- use my
intel device as the kmsro display device and add on a simulator-based v3d
device that we could render with.  But for the noop backends we use for
shader-db, it's a lot more useful to just overwrite the first render node
in the system so that you don't have to pass a -d <how many render nodes I
already have in my system> argument.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4664>

src/broadcom/drm-shim/v3d.c

@@ -28,6 +28,8 @@
 #include "v3d.h"
 #include "v3d_simulator_wrapper.h"
 
+bool drm_shim_driver_prefers_first_render_node = false;
+
 static struct v3d_device_info devinfo;
 struct v3d_shim_device v3d = {
         .devinfo = &devinfo

src/broadcom/drm-shim/v3d_noop.c

@@ -28,6 +28,8 @@
 #include "drm-uapi/v3d_drm.h"
 #include "drm-shim/drm_shim.h"
 
+bool drm_shim_driver_prefers_first_render_node = true;
+
 struct v3d_bo {
         struct shim_bo base;
         uint32_t offset;

src/drm-shim/drm_shim.c

@@ -97,9 +97,11 @@ struct file_override {
 };
 static struct file_override file_overrides[10];
 static int file_overrides_count;
+extern bool drm_shim_driver_prefers_first_render_node;
 
-/* Come up with a filename for a render node that doesn't actually exist on
- * the system.
+/* Pick the minor and filename for our shimmed render node.  This can be
+ * either a new one that didn't exist on the system, or if the driver wants,
+ * it can replace the first render node.
  */
 static void
 get_dri_render_node_minor(void)
@@ -110,7 +112,8 @@ get_dri_render_node_minor(void)
       asprintf(&render_node_path, "/dev/dri/%s",
                render_node_dirent_name);
       struct stat st;
-      if (stat(render_node_path, &st) == -1) {
+      if (drm_shim_driver_prefers_first_render_node ||
+          stat(render_node_path, &st) == -1) {
 
          render_node_minor = minor;
          return;

src/drm-shim/drm_shim.h

@@ -85,3 +85,4 @@ uint64_t drm_shim_bo_get_mmap_offset(struct shim_fd *shim_fd,
 
 /* driver-specific hooks. */
 void drm_shim_driver_init(void);
+extern bool drm_shim_driver_prefers_new_render_node;

src/etnaviv/drm-shim/etnaviv_noop.c

@@ -31,6 +31,8 @@
 #include "drm-shim/drm_shim.h"
 #include "util/u_debug.h"
 
+bool drm_shim_driver_prefers_first_render_node = true;
+
 struct etna_shim_gpu
 {
    const char *name;

src/freedreno/drm-shim/freedreno_noop.c

@@ -28,6 +28,8 @@
 #include "drm-uapi/msm_drm.h"
 #include "drm-shim/drm_shim.h"
 
+bool drm_shim_driver_prefers_first_render_node = true;
+
 struct msm_bo {
 	struct shim_bo base;
 	uint32_t offset;