udldrmfb: Fix EDID not working with monitors with EDID extension blocks

commit c930812fe5ebe725760422c9c351d1f6fde1502d upstream.

udldrmfb only reads the main EDID block, and if that advertises extensions
the drm_edid code expects them to be present, and starts reading beyond the
buffer udldrmfb passes it.

Although it may be possible to read more EDID info with the udl we simpy don't
know how, and even if trial and error gets it working on one device, that is
no guarantee it will work on other revisions. So this patch does a simple fix
in the form of patching the EDID info to report 0 extension blocks, this
fixes udldrmfb only doing 1024x768 on monitors with EDID extension blocks.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/udl/udl_connector.c b/drivers/gpu/drm/udl/udl_connector.c
index b3b2cedf674568735be66d69e4cc551d12afda04..86538c98354228c2ec58b569fe3f45e84a017458 100644 (file)
--- a/drivers/gpu/drm/udl/udl_connector.c
+++ b/drivers/gpu/drm/udl/udl_connector.c
@@ -57,6 +57,14 @@ static int udl_get_modes(struct drm_connector *connector)
 
        edid = (struct edid *)udl_get_edid(udl);
 
+       /*
+        * We only read the main block, but if the monitor reports extension
+        * blocks then the drm edid code expects them to be present, so patch
+        * the extension count to 0.
+        */
+       edid->checksum += edid->extensions;
+       edid->extensions = 0;
+
        drm_mode_connector_update_edid_property(connector, edid);
        ret = drm_add_edid_modes(connector, edid);
        kfree(edid);