[PATCH v4 6/6] drm/radeon: Switch DDC when reading the EDID

[Lukas Wunner]

The pre-retina MacBook Pro uses an LVDS panel and a gmux controller
to switch the panel between its two GPUs. The panel mode in VBIOS
is notoriously bogus on these machines.

Use drm_get_edid_switcheroo() in lieu of drm_get_edid() on LVDS.
This allows us to retrieve the EDID if the outputs are currently
muxed to the integrated GPU by temporarily switching the panel's
DDC lines to the discrete GPU.

This only enables EDID probing on the pre-retina MBP (2008 - 2013).
The retina MBP (2012 - present) uses eDP and gmux is not capable
of switching AUX separately from the main link on these models.
This will be addressed in later patches.

List of pre-retina MBPs with dual GPUs, one of them AMD:
    [MBP  8,2 2011  intel SNB + amd turks     pre-retina  15"]
    [MBP  8,3 2011  intel SNB + amd turks     pre-retina  17"]

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
Tested-by: William Brown <william at blackhats.net.au>
    [MBP  8,2 2011  intel SNB + amd turks     pre-retina  15"]

Signed-off-by: Lukas Wunner <lukas at wunner.de>
---
 drivers/gpu/drm/radeon/radeon_connectors.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/radeon/radeon_connectors.c b/drivers/gpu/drm/radeon/radeon_connectors.c
index 5a2cafb..569f63c 100644
--- a/drivers/gpu/drm/radeon/radeon_connectors.c
+++ b/drivers/gpu/drm/radeon/radeon_connectors.c
@@ -344,6 +344,10 @@ static void radeon_connector_get_edid(struct drm_connector *connector)
 		else if (radeon_connector->ddc_bus)
 			radeon_connector->edid = drm_get_edid(&radeon_connector->base,
 							      &radeon_connector->ddc_bus->adapter);
+	} else if (connector->connector_type == DRM_MODE_CONNECTOR_LVDS &&
+		   radeon_connector->ddc_bus) {
+		radeon_connector->edid = drm_get_edid_switcheroo(&radeon_connector->base,
+								 &radeon_connector->ddc_bus->adapter);
 	} else if (radeon_connector->ddc_bus) {
 		radeon_connector->edid = drm_get_edid(&radeon_connector->base,
 						      &radeon_connector->ddc_bus->adapter);
-- 
1.8.5.2 (Apple Git-48)