http://bugzilla.kernel.org/show_bug.cgi?id=12748
Summary: ACPI power resources are not disabled when unused
Product: ACPI
Version: 2.5
KernelVersion: mainline 2.6
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: Power-Other
AssignedTo: acpi_power-ot...@kernel-bugs.osdl.org
ReportedBy: h...@hmh.eng.br
Latest working kernel version: none
Earliest failing kernel version: probably all versions
Hardware Environment: ThinkPad T43
Software Environment: Linux 2.6.28 mainline
Problem Description:
Most ThinkPads have a Power Resource ("PUBS") which is used to control power to
the (internal?) USB ports. This power resource is correctly detected by Linux
and one can use sysfs to enable/disable it. So far, so good.
ACPI 3.0b, section 3.4.2 specifies that when no devices are using a power
resource, it should be turned OFF by the OS. So, if no USB HCI driver is
loaded, the power resource should be turned off.
This doesn't happen in Linux. The BIOS turns the power resource ON at boot,
and it remains untouched until power down. The kernel doesn't attempt to track
the usage of power resources, and just leaves them alone, instead of
deactivating them when not in use.
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