Re: [Resend][PATCH 0/3] ACPI / PM: Patches missing from linux-acpi-2.6/test

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Monday, December 13, 2010, ykzhao wrote:
> On Sun, 2010-12-12 at 06:39 +0800, Rafael J. Wysocki wrote:
> > Hi Len,
> > 
> > The following three patches seem to have been dropped from your 'test' branch.
> > 
> > If that happened by accident, please reapply.  Otherwise, please let me know
> > what's wrong with the patches so that I can fix them.
> > 
> > [1/3] - Make fujitsu_laptop use acpi_bus_update_power() instead of
> >         acpi_bus_get_power() which is unsafe.
> 
> It seems that the function of acpi_bus_update_power not only obtains
> the current power state, but also set the corresponding power state.
> Right?

Yes, it does.

> If the device reports the bogus power state, maybe we will set the
> incorrect power state for the corresponding device when using the
> function of acpi_bus_update_power instead of acpi_bus_get_power.

Please actually look at acpi_bus_get_power() (being removed by [2/3]) and note
that it _also_ modifies device->power.state (it doesn't return the state, actually),
so if the returned state is really bogus, we'll have a mismatch between
device->power.state and the real state of the device.  This cannot be good.

In the case of acpi_bus_update_power() we at least _try_ to keep the two things
in sync.

Note, this is _essentially_ important for power resources (if
acpi_bus_get_power() is used, the refcounts are _guaranteed_ not to be in sync
with device->power.state in some situations).

> In such case maybe the device can't work well. 
> 
> The bogus power state is reported for some devices on some laptops. For
> example: 
>     http://bugzilla.kernel.org/show_bug.cgi?id=8049
>     http://bugzilla.kernel.org/show_bug.cgi?id=11000

These bugs are about acpi_bus_set_power() doing the acpi_bus_get_power()
before setting the state, which is wrong and is being removed by my previous
patches (now in the Len's tree).

Thanks,
Rafael
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