drm/udl: limit modes to the sku pixel limits.

Otherwise when X starts we commonly get a black screen scanning
out nothing, its wierd dpms on/off from userspace brings it back,

With this on F18, multi-seat works again with my 1920x1200 monitor
which is above the sku limit for the device I have.

Cc: stable@vger.kernel.org
Reviewed-by: Alex Deucher <alexander.deucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/gpu/drm/udl/udl_connector.c b/drivers/gpu/drm/udl/udl_connector.c
index ba055e9ca007..8d9dc44f1f94 100644
--- a/drivers/gpu/drm/udl/udl_connector.c
+++ b/drivers/gpu/drm/udl/udl_connector.c
@@ -69,6 +69,13 @@ static int udl_get_modes(struct drm_connector *connector)
 static int udl_mode_valid(struct drm_connector *connector,
                           struct drm_display_mode *mode)
 {
+        struct udl_device *udl = connector->dev->dev_private;
+        if (!udl->sku_pixel_limit)
+                return 0;
+
+        if (mode->vdisplay * mode->hdisplay > udl->sku_pixel_limit)
+                return MODE_VIRTUAL_Y;
+
         return 0;
 }