drm/radeon: avoid segfault on device open when accel is not working.

When accel is not working on device with virtual address space radeon
segfault because the ib buffer is NULL and trying to map it inside the
virtual address space trigger segfault. This patch only map the ib
buffer if accel is working.

Cc: <stable@vger.kernel.org>
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/radeon/radeon_kms.c

@@ -577,6 +577,7 @@ int radeon_driver_open_kms(struct drm_device *dev, struct drm_file *file_priv)
 			return r;
 		}
 
+		if (rdev->accel_working) {
 			r = radeon_bo_reserve(rdev->ring_tmp_bo.bo, false);
 			if (r) {
 				radeon_vm_fini(rdev, &fpriv->vm);
@@ -598,7 +599,7 @@ int radeon_driver_open_kms(struct drm_device *dev, struct drm_file *file_priv)
 				kfree(fpriv);
 				return r;
 			}
-
+		}
 		file_priv->driver_priv = fpriv;
 	}
 
@@ -626,6 +627,7 @@ void radeon_driver_postclose_kms(struct drm_device *dev,
 		struct radeon_bo_va *bo_va;
 		int r;
 
+		if (rdev->accel_working) {
 			r = radeon_bo_reserve(rdev->ring_tmp_bo.bo, false);
 			if (!r) {
 				bo_va = radeon_vm_bo_find(&fpriv->vm,
@@ -634,6 +636,7 @@ void radeon_driver_postclose_kms(struct drm_device *dev,
 					radeon_vm_bo_rmv(rdev, bo_va);
 				radeon_bo_unreserve(rdev->ring_tmp_bo.bo);
 			}
+		}
 
 		radeon_vm_fini(rdev, &fpriv->vm);
 		kfree(fpriv);