ACPI: _PTS ordering needs fixing for pre ACPI 3.0 systems (was: Re: x86: Increase PCIBIOS_MIN_IO to 0x1500 to fix nForce 4 suspend-to-RAM)

[Carlos Corbacho <carlos@strangeworlds.co.uk>]

Adding Linux-ACPI to CC.

On Tuesday 25 December 2007 00:03:25 Carlos Corbacho wrote:
> According to the earlier versions of the ACPI spec, Linux is doing the
> wrong thing - we should call _PTS() before we start powerding down devices,
> or notifying device drivers to start suspending.
>
> So, my limited understanding of what we currently do for ACPI
> suspend-to-RAM is:
>
> 1) Freeze processes/ devices
> 2) Put all devices into low power mode
> 3) Execute _PTS()
> 4) Suspend system
>
> So the problem is - our current suspend order is fine for ACPI 3.0 and
> above, but for pre-3.0 systems, this violates the older specs, where 2) and
> 3) should be reversed.

The following is a hack to illustrate what I'm getting at (this is
tested on x86-64) (it's a hack since it does all the ACPI prepare bits
during set_target() for the pre ACPI 3.0 systems, rather than prepare() -
whether this can be cleaned up to move out just the _PTS() call, I don't
know).

It abuses suspend_ops->set_target(), but was the easiest way to quickly
demonstrate this (since the kerneldoc for set_target() says it will always
be executed before we suspend the devices).

-Carlos
---

 drivers/acpi/sleep/main.c |   26 ++++++++++++++++++++++----
 1 files changed, 22 insertions(+), 4 deletions(-)


diff --git a/drivers/acpi/sleep/main.c b/drivers/acpi/sleep/main.c
index 96d23b3..89e708b 100644
--- a/drivers/acpi/sleep/main.c
+++ b/drivers/acpi/sleep/main.c
@@ -77,8 +77,19 @@ static int acpi_pm_set_target(suspend_state_t pm_state)
 	} else {
 		printk(KERN_ERR "ACPI does not support this state: %d\n",
 			pm_state);
-		error = -ENOSYS;
+		return -ENOSYS;
 	}
+
+	/*
+	 * For ACPI 1.0 and 2.0 systems, we must run the preparation methods
+	 * before we put the devices into low power mode.
+	 */
+	if (acpi_gbl_FADT.header.revision < 3) {
+		error = acpi_sleep_prepare(acpi_target_sleep_state);
+		if (error)
+			acpi_target_sleep_state = ACPI_STATE_S0;
+	}
+
 	return error;
 }
 
@@ -91,10 +102,17 @@ static int acpi_pm_set_target(suspend_state_t pm_state)
 
 static int acpi_pm_prepare(void)
 {
-	int error = acpi_sleep_prepare(acpi_target_sleep_state);
+	int error = 0;
 
-	if (error)
-		acpi_target_sleep_state = ACPI_STATE_S0;
+	/*
+	 * For ACPI 3.0 or newer systems, we must run the preparation methods
+	 * after we put the devices into low power mode.
+	 */
+	if (acpi_gbl_FADT.header.revision >= 3) {
+		error = acpi_sleep_prepare(acpi_target_sleep_state);
+		if (error)
+			acpi_target_sleep_state = ACPI_STATE_S0;
+	}
 
 	return error;
 }