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

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

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.

---
 drivers/acpi/bus.c |   11 ++++++-----
 1 file changed, 6 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 +190,17 @@ 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;


> Signed-off-by: Matthew Garrett <mjg@redhat.com>
> ---
>  drivers/acpi/fan.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/acpi/fan.c b/drivers/acpi/fan.c
> index f419849..835b55e 100644
> --- a/drivers/acpi/fan.c
> +++ b/drivers/acpi/fan.c
> @@ -256,6 +256,7 @@ static int acpi_fan_add(struct acpi_device *device)
>  		goto end;
>  	}
>  
> +	device->power.flags.explicit_get = 0;
>  	device->flags.force_power_state = 1;
>  	acpi_bus_set_power(device->handle, state);
>  	device->flags.force_power_state = 0;

at least we should clear the explicit_get flag 6 lines above, i.e.
before getting the fan state?

thanks,
rui