linux-kernel - [PATCH] acpi: Fall back to manually changing SCI

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Date:	Mon, 19 Apr 2010 17:13:34 -0400
From:	Matthew Garrett <mjg@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-acpi@...r.kernel.org, lenb@...nel.org,
	Matthew Garrett <mjg@...hat.com>
Subject: [PATCH] acpi: Fall back to manually changing SCI_EN

The ACPI spec tells us that the ACPI SCI_EN bit is under hardware control
and shouldn't be touched by the OS. It seems that the Leading Other OS
ignores this and some machines expect this behaviour. We have a blacklist
for these, but given that we're able to detect the failure case and the
alternative to breaking the spec is letting the machine crash and burn,
let's try falling back when we know the alternative is a mostly-dead
machine.

Signed-off-by: Matthew Garrett <mjg@...hat.com>
---
 drivers/acpi/sleep.c |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/sleep.c b/drivers/acpi/sleep.c
index f74834a..79df8d4 100644
--- a/drivers/acpi/sleep.c
+++ b/drivers/acpi/sleep.c
@@ -227,6 +227,7 @@ static int acpi_suspend_begin(suspend_state_t pm_state)
 static int acpi_suspend_enter(suspend_state_t pm_state)
 {
 	acpi_status status = AE_OK;
+	acpi_status enable_status = AE_OK;
 	unsigned long flags = 0;
 	u32 acpi_state = acpi_target_sleep_state;
 
@@ -254,10 +255,19 @@ static int acpi_suspend_enter(suspend_state_t pm_state)
 	}
 
 	/* If ACPI is not enabled by the BIOS, we need to enable it here. */
-	if (set_sci_en_on_resume)
+	if (!set_sci_en_on_resume)
+		enable_status = acpi_enable();
+
+	if (set_sci_en_on_resume || enable_status == AE_NO_HARDWARE_RESPONSE)
+		/* If we're still in legacy mode then we have a problem. The
+		 * spec tells us that this bit is under hardware control, but
+		 * there's no plausible way that the OS can transition back to
+		 * legacy mode so our choices here are to either ignore the
+		 * spec or crash and burn horribly. The latter doesn't seem
+		 * like it's ever going to be the preferable choice, so let's
+		 * live dangerously.
+		 */
 		acpi_write_bit_register(ACPI_BITREG_SCI_ENABLE, 1);
-	else
-		acpi_enable();
 
 	/* Reprogram control registers and execute _BFS */
 	acpi_leave_sleep_state_prep(acpi_state);
-- 
1.7.0.1

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