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a2d7b2e004
If an ACPI wakeup power resource is shared between multiple devices,
it may not be managed correctly.
Suppose, for example, that two devices, A and B, share a wakeup power
resource P whose wakeup_enabled flag is 0 initially. Next, suppose
that wakeup power is enabled for A and B, in this order, and disabled
for B. When wakeup power is enabled for A, P will be turned on and
its wakeup_enabled flag will be set. Next, when wakeup power is
enabled for B, P will not be touched, because its wakeup_enabled flag
is set. Now, when wakeup power is disabled for B, P will be turned
off which is incorrect, because A will still need P in order to signal
wakeup.
Moreover, if wakeup power is enabled for A and then disabled for B,
the latter will cause P to be turned off incorrectly (it will be still
needed by A), because acpi_disable_wakeup_device_power() is allowed
to manipulate power resources when the wakeup.prepare_count counter
of the given device is 0.
While the first issue could be addressed by changing the
wakeup_enabled power resource flag into a counter, addressing the
second one requires modifying acpi_disable_wakeup_device_power() to
do nothing when the target device's wakeup.prepare_count reference
counter is zero and that would cause the new counter to be redundant.
Namely, if acpi_disable_wakeup_device_power() is modified as per the
above, every change of the new counter following a wakeup.prepare_count
change would be reflected by the analogous change of the main reference
counter of the given power resource.
Accordingly, modify acpi_disable_wakeup_device_power() to do nothing
when the target device's wakeup.prepare_count reference counter is
zero and drop the power resource wakeup_enabled flag altogether.
While at it, ensure that all of the power resources that can be
turned off will be turned off when disabling device wakeup due to
a power resource manipulation error, to prevent energy from being
wasted.
Fixes: b5d667eb39 ("ACPI / PM: Take unusual configurations of power resources into account")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Linux kernel
============
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