[PATCH v2] drm/radeon: fix null pointer dereference in radeon_add_common_modes

[Ma Ke]

In radeon_add_common_modes(), the return value of drm_cvt_mode() is
assigned to mode, which will lead to a possible NULL pointer dereference
on failure of drm_cvt_mode(). Add a check to avoid npd.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: d50ba256b5f1 ("drm/kms: start adding command line interface using fb.")
Signed-off-by: Ma Ke <make24@xxxxxxxxxxx>
---
Changes in v2:
- added a blank line;
- added Cc line.
---
 drivers/gpu/drm/radeon/radeon_connectors.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/radeon/radeon_connectors.c b/drivers/gpu/drm/radeon/radeon_connectors.c
index b84b58926106..37c56c16af8d 100644
--- a/drivers/gpu/drm/radeon/radeon_connectors.c
+++ b/drivers/gpu/drm/radeon/radeon_connectors.c
@@ -520,6 +520,9 @@ static void radeon_add_common_modes(struct drm_encoder *encoder, struct drm_conn
 			continue;
 
 		mode = drm_cvt_mode(dev, common_modes[i].w, common_modes[i].h, 60, false, false, false);
+		if (!mode)
+			continue;
+
 		drm_mode_probed_add(connector, mode);
 	}
 }
-- 
2.25.1