renderer/native: Add udev rule to select primary GPU

Sometimes the automatically selected primary GPU isn't suitable with no
way to make an well educated guess to do it better. To make it possible
for the user to override the automatically calculated default, make it
possible to override it using a udev rule.

E.g. to select /dev/dri/card1 as the primary GPU, add a file e.g.
/usr/lib/udev/rules.d/61-mutter-primary-gpu.rules (path my vary
depending on distribution) containing the fellowing line:

ENV{DEVNAME}=="/dev/dri/card1", TAG+="mutter-device-preferred-primary"

Reboot or manual triggering of udev rules to make it take effect may be
required.

Related: https://gitlab.gnome.org/GNOME/mutter/merge_requests/1057

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1562

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1562>

src/backends/native/meta-backend-native.c

@@ -373,6 +373,9 @@ create_gpu_from_udev_device (MetaBackendNative  *native,
   if (meta_is_udev_device_requires_modifiers (device))
     flags |= META_KMS_DEVICE_FLAG_REQUIRES_MODIFIERS;
 
+  if (meta_is_udev_device_preferred_primary (device))
+    flags |= META_KMS_DEVICE_FLAG_PREFERRED_PRIMARY;
+
   device_path = g_udev_device_get_device_file (device);
 
   kms_device = meta_kms_create_device (native->kms, device_path, flags,

src/backends/native/meta-kms-types.h

@@ -57,6 +57,7 @@ typedef enum _MetaKmsDeviceFlag
   META_KMS_DEVICE_FLAG_BOOT_VGA = 1 << 0,
   META_KMS_DEVICE_FLAG_PLATFORM_DEVICE = 1 << 1,
   META_KMS_DEVICE_FLAG_REQUIRES_MODIFIERS = 1 << 2,
+  META_KMS_DEVICE_FLAG_PREFERRED_PRIMARY = 1 << 3,
 } MetaKmsDeviceFlag;
 
 typedef enum _MetaKmsPlaneType MetaKmsPlaneType;

src/backends/native/meta-renderer-native.c

@@ -64,6 +64,7 @@
 #include "backends/native/meta-drm-buffer-import.h"
 #include "backends/native/meta-drm-buffer.h"
 #include "backends/native/meta-gpu-kms.h"
+#include "backends/native/meta-kms-device.h"
 #include "backends/native/meta-kms-update.h"
 #include "backends/native/meta-kms-utils.h"
 #include "backends/native/meta-kms.h"
@@ -3752,6 +3753,21 @@ choose_primary_gpu_unchecked (MetaBackend        *backend,
    */
   for (allow_sw = 0; allow_sw < 2; allow_sw++)
   {
+    /* First check if one was explicitly configured. */
+    for (l = gpus; l; l = l->next)
+      {
+        MetaGpuKms *gpu_kms = META_GPU_KMS (l->data);
+        MetaKmsDevice *kms_device = meta_gpu_kms_get_kms_device (gpu_kms);
+
+        if (meta_kms_device_get_flags (kms_device) &
+            META_KMS_DEVICE_FLAG_PREFERRED_PRIMARY)
+          {
+            g_message ("GPU %s selected primary given udev rule",
+                       meta_gpu_kms_get_file_path (gpu_kms));
+            return gpu_kms;
+          }
+      }
+
     /* Prefer a platform device */
     for (l = gpus; l; l = l->next)
       {
@@ -3760,8 +3776,12 @@ choose_primary_gpu_unchecked (MetaBackend        *backend,
         if (meta_gpu_kms_is_platform_device (gpu_kms) &&
             (allow_sw == 1 ||
              gpu_kms_is_hardware_rendering (renderer_native, gpu_kms)))
+          {
+            g_message ("Integrated GPU %s selected as primary",
+                       meta_gpu_kms_get_file_path (gpu_kms));
             return gpu_kms;
           }
+      }
 
     /* Otherwise a device we booted with */
     for (l = gpus; l; l = l->next)
@@ -3771,8 +3791,12 @@ choose_primary_gpu_unchecked (MetaBackend        *backend,
         if (meta_gpu_kms_is_boot_vga (gpu_kms) &&
             (allow_sw == 1 ||
              gpu_kms_is_hardware_rendering (renderer_native, gpu_kms)))
+          {
+            g_message ("Boot VGA GPU %s selected as primary",
+                       meta_gpu_kms_get_file_path (gpu_kms));
             return gpu_kms;
           }
+      }
 
     /* Fall back to any device */
     for (l = gpus; l; l = l->next)
@@ -3781,9 +3805,13 @@ choose_primary_gpu_unchecked (MetaBackend        *backend,
 
         if (allow_sw == 1 ||
             gpu_kms_is_hardware_rendering (renderer_native, gpu_kms))
+          {
+            g_message ("GPU %s selected as primary",
+                       meta_gpu_kms_get_file_path (gpu_kms));
             return gpu_kms;
           }
       }
+  }
 
   g_assert_not_reached ();
   return NULL;

src/backends/native/meta-udev.c

@@ -95,6 +95,18 @@ meta_is_udev_device_requires_modifiers (GUdevDevice *device)
   return g_strv_contains (tags, "mutter-device-requires-kms-modifiers");
 }
 
+gboolean
+meta_is_udev_device_preferred_primary (GUdevDevice *device)
+{
+  const char * const * tags;
+
+  tags = g_udev_device_get_tags (device);
+  if (!tags)
+    return FALSE;
+
+  return g_strv_contains (tags, "mutter-device-preferred-primary");
+}
+
 gboolean
 meta_udev_is_drm_device (MetaUdev    *udev,
                          GUdevDevice *device)

src/backends/native/meta-udev.h

@@ -34,6 +34,8 @@ gboolean meta_is_udev_device_boot_vga (GUdevDevice *device);
 
 gboolean meta_is_udev_device_requires_modifiers (GUdevDevice *device);
 
+gboolean meta_is_udev_device_preferred_primary (GUdevDevice *device);
+
 gboolean meta_udev_is_drm_device (MetaUdev    *udev,
                                   GUdevDevice *device);