[PATCH v3 2/6] apple-gmux: Add switch_ddc support

[Lukas Wunner]

Originally by Seth Forshee <seth.forshee at canonical.com>, 2012-10-04:
    The gmux allows muxing the DDC independently from the display, so
    support this functionality. This will allow reading the EDID for the
    inactive GPU, fixing issues with machines that either don't have a
    VBT or have invalid mode data in the VBT.

Modified by Lukas Wunner <lukas at wunner.de>, 2015-08-28:
    Retain semantics of ->switchto handler callback to switch all pins,
    including DDC. Change semantics of ->switch_ddc handler callback to
    return previous DDC owner. Original version tried to determine
    previous DDC owner with find_active_client() in vga_switcheroo but
    this fails if the inactive client registers before the active
    client.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
Tested-by: Pierre Moreau <pierre.morrow at free.fr>
    [MBP  5,3 2009  nvidia MCP79 + G96        pre-retina  15"]
Tested-by: William Brown <william at blackhats.net.au>
    [MBP  8,2 2011  intel SNB + amd turks     pre-retina  15"]
Tested-by: Lukas Wunner <lukas at wunner.de>
    [MBP  9,1 2012  intel IVB + nvidia GK107  pre-retina  15"]

Cc: Seth Forshee <seth.forshee at canonical.com>
Signed-off-by: Lukas Wunner <lukas at wunner.de>
---
 drivers/platform/x86/apple-gmux.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
index 0dec3f5..5bb231b 100644
--- a/drivers/platform/x86/apple-gmux.c
+++ b/drivers/platform/x86/apple-gmux.c
@@ -273,6 +273,28 @@ static const struct backlight_ops gmux_bl_ops = {
 	.update_status = gmux_update_status,
 };
 
+static int gmux_switch_ddc(enum vga_switcheroo_client_id id)
+{
+	enum vga_switcheroo_client_id old_ddc_owner;
+
+	if (gmux_read8(apple_gmux_data, GMUX_PORT_SWITCH_DDC) == 1)
+		old_ddc_owner = VGA_SWITCHEROO_IGD;
+	else
+		old_ddc_owner = VGA_SWITCHEROO_DIS;
+
+	pr_debug("Switching gmux DDC from %d to %d\n", old_ddc_owner, id);
+
+	if (id == old_ddc_owner)
+		return old_ddc_owner;
+
+	if (id == VGA_SWITCHEROO_IGD)
+		gmux_write8(apple_gmux_data, GMUX_PORT_SWITCH_DDC, 1);
+	else
+		gmux_write8(apple_gmux_data, GMUX_PORT_SWITCH_DDC, 2);
+
+	return old_ddc_owner;
+}
+
 static int gmux_switchto(enum vga_switcheroo_client_id id)
 {
 	if (id == VGA_SWITCHEROO_IGD) {
@@ -348,6 +370,7 @@ gmux_active_client(struct apple_gmux_data *gmux_data)
 
 static struct vga_switcheroo_handler gmux_handler = {
 	.switchto = gmux_switchto,
+	.switch_ddc = gmux_switch_ddc,
 	.power_state = gmux_set_power_state,
 	.get_client_id = gmux_get_client_id,
 };
-- 
1.8.5.2 (Apple Git-48)