[PATCH] apple-gmux: Restore switch registers on suspend/resume

[PATCH] apple-gmux: Restore switch registers on suspend/resume

[Arun Raghavan]

After suspend and resume, the values of these registers seem to change
from what they were at suspend time, potentially preventing the actual
output lines from being enabled post-resume. This saves relevant state
at suspend and restores it when resumed.

This is at least required on the MacBook Pro 8.2 when the Intel GPU is
manually selected in GRUB config before the kernel is loaded.

Signed-off-by: Arun Raghavan <arun.raghavan@collabora.co.uk>
---
 drivers/platform/x86/apple-gmux.c |   29 ++++++++++++++++++++++++++++-
 1 files changed, 28 insertions(+), 1 deletions(-)

diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
index 694a15a..5a5d005 100644
--- a/drivers/platform/x86/apple-gmux.c
+++ b/drivers/platform/x86/apple-gmux.c
@@ -26,6 +26,11 @@ struct apple_gmux_data {
 	unsigned long iolen;
 
 	struct backlight_device *bdev;
+
+	bool was_suspended;
+	u8 save_switch_ddc;
+	u8 save_switch_disp;
+	u8 save_switch_ext;
 };
 
 /*
@@ -87,8 +92,30 @@ static int gmux_update_status(struct backlight_device *bd)
 	struct apple_gmux_data *gmux_data = bl_get_data(bd);
 	u32 brightness = bd->props.brightness;
 
-	if (bd->props.state & BL_CORE_SUSPENDED)
+	if (bd->props.state & BL_CORE_SUSPENDED) {
+		/* Save mux settings for output lines since they get reset on
+		 * suspend */
+		gmux_data->was_suspended = TRUE;
+		gmux_data->save_switch_ddc = gmux_read8(gmux_data,
+				GMUX_PORT_SWITCH_DDC);
+		gmux_data->save_switch_disp = gmux_read8(gmux_data,
+				GMUX_PORT_SWITCH_DISPLAY);
+		gmux_data->save_switch_ext = gmux_read8(gmux_data,
+				GMUX_PORT_SWITCH_EXTERNAL);
+
 		return 0;
+	}
+
+	if (gmux_data->was_suspended) {
+		/* Restore pre-suspend values for output lines */
+		gmux_data->was_suspended = FALSE;
+		gmux_write8(gmux_data, GMUX_PORT_SWITCH_DDC,
+				gmux_data->save_switch_ddc);
+		gmux_write8(gmux_data, GMUX_PORT_SWITCH_DISPLAY,
+				gmux_data->save_switch_disp);
+		gmux_write8(gmux_data, GMUX_PORT_SWITCH_EXTERNAL,
+				gmux_data->save_switch_ext);
+	}
 
 	/*
 	 * Older gmux versions require writing out lower bytes first then
-- 
1.7.8.6

Re: [PATCH] apple-gmux: Restore switch registers on suspend/resume

[Seth Forshee]

On Tue, Jul 10, 2012 at 09:09:53AM +0530, Arun Raghavan wrote:
> After suspend and resume, the values of these registers seem to change
> from what they were at suspend time, potentially preventing the actual
> output lines from being enabled post-resume. This saves relevant state
> at suspend and restores it when resumed.
> 
> This is at least required on the MacBook Pro 8.2 when the Intel GPU is
> manually selected in GRUB config before the kernel is loaded.

I've got a couple of problems with this. The first is that the backlight
update_status callback isn't an appropriate place to do this. Adding
suspend/resume ops for the pnp_driver would be better.

But the more serious concern is whether or not its safe to simply
restore the register values. I know that the reverse engineering work
done on the gmux has revealed a particular sequence for selecting the
active GPU. A brute force restoration of the registers disregards this
sequencing, which doesn't seem like a good idea.

Seth