[PATCH v4 5/6] drm/nouveau: 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 other GPU by temporarily switching the panel's DDC
lines. Likewise, ask vga_switcheroo to switch DDC before probing
LVDS connectors.

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, either or both Nvidia:
    [MBP  5,1 2008  nvidia MCP79 + G96        pre-retina  15"]
    [MBP  5,2 2009  nvidia MCP79 + G96        pre-retina  17"]
    [MBP  5,3 2009  nvidia MCP79 + G96        pre-retina  15"]
    [MBP  6,2 2010  intel ILK + nvidia GT216  pre-retina  15"]
    [MBP  6,1 2010  intel ILK + nvidia GT216  pre-retina  17"]
    [MBP  9,1 2012  intel IVB + nvidia GK107  pre-retina  15"]

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
Tested-by: Lukas Wunner <lukas at wunner.de>
    [MBP  9,1 2012  intel IVB + nvidia GK107  pre-retina  15"]

Signed-off-by: Lukas Wunner <lukas at wunner.de>
---
 drivers/gpu/drm/nouveau/nouveau_connector.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_connector.c b/drivers/gpu/drm/nouveau/nouveau_connector.c
index 2e7cbe9..fb12c9e 100644
--- a/drivers/gpu/drm/nouveau/nouveau_connector.c
+++ b/drivers/gpu/drm/nouveau/nouveau_connector.c
@@ -27,6 +27,7 @@
 #include <acpi/button.h>
 
 #include <linux/pm_runtime.h>
+#include <linux/vga_switcheroo.h>
 
 #include <drm/drmP.h>
 #include <drm/drm_edid.h>
@@ -148,7 +149,13 @@ nouveau_connector_ddc_detect(struct drm_connector *connector)
 				break;
 		} else
 		if (nv_encoder->i2c) {
-			if (nvkm_probe_i2c(nv_encoder->i2c, 0x50))
+			int ret;
+			if (nv_encoder->dcb->type == DCB_OUTPUT_LVDS)
+				vga_switcheroo_lock_ddc(dev->pdev);
+			ret = nvkm_probe_i2c(nv_encoder->i2c, 0x50);
+			if (nv_encoder->dcb->type == DCB_OUTPUT_LVDS)
+				vga_switcheroo_unlock_ddc();
+			if (ret)
 				break;
 		}
 	}
@@ -259,7 +266,9 @@ nouveau_connector_detect(struct drm_connector *connector, bool force)
 
 	nv_encoder = nouveau_connector_ddc_detect(connector);
 	if (nv_encoder && (i2c = nv_encoder->i2c) != NULL) {
-		nv_connector->edid = drm_get_edid(connector, i2c);
+		nv_connector->edid = nv_encoder->dcb->type == DCB_OUTPUT_LVDS ?
+				     drm_get_edid_switcheroo(connector, i2c) :
+				     drm_get_edid(connector, i2c);
 		drm_mode_connector_update_edid_property(connector,
 							nv_connector->edid);
 		if (!nv_connector->edid) {
-- 
1.8.5.2 (Apple Git-48)