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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2013-10-16 23:05:42 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2013-10-16 23:05:42 +0200
commit41863fcee3039ec3de15003b78e7284c4393e862 (patch)
tree0a5019735c7c4835dd697cf8ae5aa449c341b601 /drivers/regulator/lp8788-ldo.c
parentACPI: remove /proc/acpi/event from ACPI_BUTTON help (diff)
downloadlinux-41863fcee3039ec3de15003b78e7284c4393e862.tar.xz
linux-41863fcee3039ec3de15003b78e7284c4393e862.zip
ACPI / power: Drop automaitc resume of power resource dependent devices
The mechanism causing devices depending on a given power resource (that is, devices that can be in D0 only if that power resource is on) to be resumed automatically when the power resource is turned on (and their "inferred" power state becomes D0 as a result) is inherently racy and in fact unnecessary. It is racy, because if the power resource is turned on and then immediately off, the device resume triggered by the first transition to "on" may still happen, causing the power resource to be turned on again. That again will trigger the "resume of dependent devices" mechanism, but if the devices in question are not in use, they will be suspended in the meantime causing the power resource to be turned off. However, the "resume of dependent devices" will next resume them again and so on. In some cases (USB port PM in particular) that leads to an endless busy loop of flipping the resource on and off continuously. It is needless, because whoever turns a power resource on will most likely turn it off at some point and the devices that go into "D0" as a result of turning it on will then go back into D3cold (generally, the state they were in before). Moreover, turning on all power resources a device needs to go into D0 is not sufficient for a full transition into D0 in general. Namely, _PS0 may need to be executed in addition to that in some cases. This means that the whole rationale of the "resume of dependent devices" mechanism was incorrect to begin with and it's best to remove it entirely. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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