Re: [PATCH] acpi: Disable explicit power state retrieval on fans

[Zhang Rui <rui.zhang@intel.com>]

On Fri, 2009-12-11 at 11:52 +0800, Zhang Rui wrote:
> On Wed, 2009-11-11 at 04:09 +0800, Matthew Garrett wrote:
> > https://bugzilla.redhat.com/show_bug.cgi?id=531916 describes a system
> > with a _PSC method for the fan that always returns "on". There's no
> > benefit in us always requesting the state of the fan when performing
> > transitions - we want to do everything we can to ensure that the fan turns
> > on when it should do, not risk hardware damage by believing the hardware
> > when it tells us the fan is already on. Given that the Leading Other OS(tm)
> > works fine on this machine, it seems likely that it behaves in much this
> > way.
> > 
> sounds reasonable.
> But how can we get the power state if power resources is not available?
> 
> In acpi_bus_get_power, why not make acpi_power_get_inferred_state as the
> first choice, instead of evaluating _PSC? like the patch attached.
> 
Matthew,

how about this one?


If the ACPI power state can be got both directly and indirectly,
we prefer to get it indirectly.

https://bugzilla.redhat.com/show_bug.cgi?id=531916 describes a
system with a _PSC method for the fan that always returns "on".
There's no benefit in us always requesting the state of the fan
when performing transitions - we want to do everything we can
to ensure that the fan turns on when it should do, not risk
hardware damage by believing the hardware when it tells us the
fan is already on. Given that the Leading Other OS(tm) works fine
on this machine, it seems likely that it behaves in much this way.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
---
 drivers/acpi/bus.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

Index: linux-2.6/drivers/acpi/bus.c
===================================================================
--- linux-2.6.orig/drivers/acpi/bus.c
+++ linux-2.6/drivers/acpi/bus.c
@@ -190,16 +190,16 @@ int acpi_bus_get_power(acpi_handle handl
 		 * Get the device's power state either directly (via _PSC) or
 		 * indirectly (via power resources).
 		 */
-		if (device->power.flags.explicit_get) {
+		if (device->power.flags.power_resources) {
+			result = acpi_power_get_inferred_state(device);
+			if (result)
+				return result;
+		} else if (device->power.flags.explicit_get) {
 			status = acpi_evaluate_integer(device->handle, "_PSC",
 						       NULL, &psc);
 			if (ACPI_FAILURE(status))
 				return -ENODEV;
 			device->power.state = (int)psc;
-		} else if (device->power.flags.power_resources) {
-			result = acpi_power_get_inferred_state(device);
-			if (result)
-				return result;
 		}
 
 		*state = device->power.state;