[PATCH v4 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>, 2015-10-07:
    Advertise ->switch_ddc handler callback only on the pre-retina
    Macbook Pro. The retina uses eDP and its mux is incapable of
    switching the AUX channel separately from the main link.
    It's an NXP CBTL06142 (alternate parts: TI HD3SS212,
    Pericom PPI3VDP12412).

    Sources:
    http://www.electronicproducts.com/-whatsinside_text-145.aspx
    http://slideshare.net/jjwu6266/apple-2012-wwdc-apple-macbook-pro-with-retina-display
    http://www.techrepublic.com/blog/cracking-open/teardown-shows-retina-macbook-pro-is-nearly-impossible-to-upgrade-difficult-to-work-on/

    Datasheets:
    http://www.nxp.com/documents/data_sheet/CBTL06141.pdf
    http://www.ti.com/lit/ds/symlink/hd3ss212.pdf
    https://www.pericom.com/assets/Datasheets/PI3VDP12412.pdf

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"]

Cc: Seth Forshee <seth.forshee at canonical.com>
Signed-off-by: Lukas Wunner <lukas at wunner.de>
---
 drivers/platform/x86/apple-gmux.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
index 0dec3f5..78997b7 100644
--- a/drivers/platform/x86/apple-gmux.c
+++ b/drivers/platform/x86/apple-gmux.c
@@ -276,11 +276,9 @@ static const struct backlight_ops gmux_bl_ops = {
 static int gmux_switchto(enum vga_switcheroo_client_id id)
 {
 	if (id == VGA_SWITCHEROO_IGD) {
-		gmux_write8(apple_gmux_data, GMUX_PORT_SWITCH_DDC, 1);
 		gmux_write8(apple_gmux_data, GMUX_PORT_SWITCH_DISPLAY, 2);
 		gmux_write8(apple_gmux_data, GMUX_PORT_SWITCH_EXTERNAL, 2);
 	} else {
-		gmux_write8(apple_gmux_data, GMUX_PORT_SWITCH_DDC, 2);
 		gmux_write8(apple_gmux_data, GMUX_PORT_SWITCH_DISPLAY, 3);
 		gmux_write8(apple_gmux_data, GMUX_PORT_SWITCH_EXTERNAL, 3);
 	}
@@ -288,6 +286,18 @@ static int gmux_switchto(enum vga_switcheroo_client_id id)
 	return 0;
 }
 
+static int gmux_switch_ddc(enum vga_switcheroo_client_id id)
+{
+	pr_debug("Switching gmux DDC to %d\n", id);
+
+	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 0;
+}
+
 static int gmux_set_discrete_state(struct apple_gmux_data *gmux_data,
 				   enum vga_switcheroo_state state)
 {
@@ -588,6 +598,13 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
 		gmux_data->gpe = -1;
 	}
 
+	/*
+	 * The gmux in pre-retina MacBook Pros can switch DDC separately
+	 * from the other pins of the outputs. It's distinguishable from
+	 * the gmux in retinas by being non-indexed.
+	 */
+	if (!gmux_data->indexed)
+		gmux_handler.switch_ddc = gmux_switch_ddc;
 	if (vga_switcheroo_register_handler(&gmux_handler)) {
 		ret = -ENODEV;
 		goto err_register_handler;
-- 
1.8.5.2 (Apple Git-48)