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
2007-12-25T02:41:48Z

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;
}