drm/radeon: make MMU_NOTIFIER optional

In cases where MMU_NOTIFIER is not available, userptr will not be
available.  Similar to i915, although not making an exception for
CAP_SYS_ADMIN.

The proposed userspace patches for userptr seem to handle the fall-
back properly, so a userptr-less kernel should not be a problem.
Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/Kconfig

@@ -110,7 +110,6 @@ config DRM_RADEON
 	select HWMON
 	select BACKLIGHT_CLASS_DEVICE
 	select INTERVAL_TREE
-	select MMU_NOTIFIER
 	help
 	  Choose this option if you have an ATI Radeon graphics card.  There
 	  are both PCI and AGP versions.  You don't need to choose this to

drivers/gpu/drm/radeon/Makefile

@@ -80,9 +80,11 @@ radeon-y += radeon_device.o radeon_asic.o radeon_kms.o \
 	r600_dpm.o rs780_dpm.o rv6xx_dpm.o rv770_dpm.o rv730_dpm.o rv740_dpm.o \
 	rv770_smc.o cypress_dpm.o btc_dpm.o sumo_dpm.o sumo_smc.o trinity_dpm.o \
 	trinity_smc.o ni_dpm.o si_smc.o si_dpm.o kv_smc.o kv_dpm.o ci_smc.o \
-	ci_dpm.o dce6_afmt.o radeon_vm.o radeon_ucode.o radeon_ib.o radeon_mn.o \
+	ci_dpm.o dce6_afmt.o radeon_vm.o radeon_ucode.o radeon_ib.o \
 	radeon_sync.o radeon_audio.o
 
+radeon-$(CONFIG_MMU_NOTIFIER) += radeon_mn.o
+
 # add async DMA block
 radeon-y += \
 	r600_dma.o \

drivers/gpu/drm/radeon/radeon.h

@@ -1780,8 +1780,16 @@ void radeon_test_syncing(struct radeon_device *rdev);
 /*
  * MMU Notifier
  */
+#if defined(CONFIG_MMU_NOTIFIER)
 int radeon_mn_register(struct radeon_bo *bo, unsigned long addr);
 void radeon_mn_unregister(struct radeon_bo *bo);
+#else
+static inline int radeon_mn_register(struct radeon_bo *bo, unsigned long addr)
+{
+	return -ENODEV;
+}
+static inline void radeon_mn_unregister(struct radeon_bo *bo) {}
+#endif
 
 /*
  * Debugfs