On Sunday 24 June 2007, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <[EMAIL PROTECTED]>
>
> Some drivers may need to use ACPI to determine the low power states in which
> to place their devices, but to provide the drivers with this information the
> ACPI core needs to know what sleep state the system is going to enter.
It also needs to export that to things like the ACPI-to-PCI glue
code. So it would be good if you defined the missing routine now,
saving the effort of patching it in later:
int acpi_get_target_sleep_state(void);
It doesn't need EXPORT_SYMBOL().
> Namely, the device's state should not be too high power for given system sleep
> state and, if the device is supposed to be able to wake up the system, its
> state
> should not be too low power for the wake up to be possible). However,
> pm_ops->prepare() is only called after the drivers' .suspend() callbacks have
> been executed,
That's a critical point that should show up in your doc updates.
> so we need an additional means to pass the information of the
> target system sleep state to the ACPI core. For this purpose, we can
> introduce
> an additional member function in 'struct pm_ops'.
>
> Additionally, the at91 platform code incorrectly assumes that
> pm_ops->prepare()
> will be called before devices are suspended and uses it for setting the target
> system sleep state, so pm_ops->prepare() should to be replaced with the new
> operation, pm_ops->set_target(), for this architecture.
That was originally correct ... but as you pointed out, the
semantics there changed in RC5.
Which means this patch is a *BUGFIX*, preventing what would
otherwise be a regression in 2.6.22 ... and so it should
be merged for RC6 or so.
Another way to describe the changes is that set_target() now
does what prepare() used to do, while prepare() serves a
new role. A role which still needs to be well-described in
the documentation you provided, by the way... it seems to
do whatever needs to be done after devices suspend but
before nonboot CPUs are disabled.
- Dave
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