[PATCH v2 04/22] drm/edid: Switch DDC when reading the EDID

[Lukas Wunner]

From: Seth Forshee <seth.forshee at canonical.com>

Some dual graphics machines support muxing the DDC separately from the
display, so make use of this functionality when reading the EDID on the
inactive GPU. Also serialize drm_get_edid() with a mutex to avoid races
on the DDC mux state.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
Tested-by: Paul Hordiienko <pvt.gord at gmail.com>
    [MBP  6,2 2010  intel ILK + nvidia GT216  pre-retina]
Tested-by: William Brown <william at blackhats.net.au>
    [MBP  8,2 2011  intel SNB + amd turks     pre-retina]
Tested-by: Lukas Wunner <lukas at wunner.de>
    [MBP  9,1 2012  intel IVB + nvidia GK107  pre-retina]
Tested-by: Bruno Bierbaumer <bruno at bierbaumer.net>
    [MBP 11,3 2013  intel HSW + nvidia GK107  retina -- work in progress]

Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
Signed-off-by: Dave Airlie <airlied at gmail.com>
Signed-off-by: Lukas Wunner <lukas at wunner.de>
---
 drivers/gpu/drm/drm_edid.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index e6e05bb..2424aef 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -32,6 +32,7 @@
 #include <linux/hdmi.h>
 #include <linux/i2c.h>
 #include <linux/module.h>
+#include <linux/vga_switcheroo.h>
 #include <drm/drmP.h>
 #include <drm/drm_edid.h>
 #include <drm/drm_displayid.h>
@@ -87,6 +88,8 @@ struct detailed_mode_closure {
 #define LEVEL_GTF2	2
 #define LEVEL_CVT	3
 
+static DEFINE_MUTEX(drm_edid_mutex);
+
 static struct edid_quirk {
 	char vendor[4];
 	int product_id;
@@ -1377,6 +1380,16 @@ struct edid *drm_get_edid(struct drm_connector *connector,
 			  struct i2c_adapter *adapter)
 {
 	struct edid *edid;
+	struct pci_dev *pdev = connector->dev->pdev;
+	struct pci_dev *active_pdev = NULL;
+
+	mutex_lock(&drm_edid_mutex);
+
+	if (pdev) {
+		active_pdev = vga_switcheroo_get_active_client();
+		if (active_pdev != pdev)
+			vga_switcheroo_switch_ddc(pdev);
+	}
 
 	if (!drm_probe_ddc(adapter))
 		return NULL;
@@ -1384,6 +1397,11 @@ struct edid *drm_get_edid(struct drm_connector *connector,
 	edid = drm_do_get_edid(connector, drm_do_probe_ddc_edid, adapter);
 	if (edid)
 		drm_get_displayid(connector, edid);
+
+	if (active_pdev && active_pdev != pdev)
+		vga_switcheroo_switch_ddc(active_pdev);
+
+	mutex_unlock(&drm_edid_mutex);
 	return edid;
 }
 EXPORT_SYMBOL(drm_get_edid);
-- 
1.8.5.2 (Apple Git-48)