• Rafael J. Wysocki's avatar
    ACPI / PM: Make acpi_bus_init_power() more robust · a2367807
    Rafael J. Wysocki authored
    The ACPI specification requires the _PSC method to be present under
    a device object if its power state cannot be inferred from the states
    of power resources used by it (ACPI 5, Section 7.6.2).  However, it
    also requires that (for power states D0-D2 and D3hot) if the _PSn
    (n = 0, 1, 2, 3) method is present under the device object, it also
    must be executed after the power resources have been set
    appropriately for the device to go into power state Dn (D3 means
    D3hot in this case).  Thus it is not clear from the specification
    whether or not the _PSn method should be executed if the initial
    configuraion of power resources used by the device indicates power
    state Dn and the _PSC method is not present.
    
    The current implementation of acpi_bus_init_power() is based on the
    assumption that it should not be necessary to execute _PSn in the
    above situation, but experience shows that in fact that assumption
    need not be satisfied.  For this reason, make acpi_bus_init_power()
    always execute _PSn if the initial configuration of device power
    resources indicates power state Dn.
    Reported-and-tested-by: default avatarMika Westerberg <mika.westerberg@linux.intel.com>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    a2367807
device_pm.c 28.8 KB