1. 04 Apr, 2009 1 commit
    • Witold Szczeponik's avatar
      Enable PNPACPI _PSx Support, v3 · 6328a574
      Witold Szczeponik authored
      (This is an update to the patch presented earlier in
      http://lkml.org/lkml/2008/12/8/284, with new error handling.)
      
      This patch sets the power of PnP ACPI devices to D0 when they
      are activated and to D3 when they are disabled.  The latter is
      in correspondence with the ACPI 3.0 specification, whereas the
      former is added in order to be able to power up a device after
      it has been previously disabled (or when booting up a system).
      (As a consequence, the patch makes the PnP ACPI code more ACPI
      compliant.)
      
      Section 6.2.2 of the ACPI Specification (at least versions 1.0b
      and 3.0a) states: "Prior to running this control method [_DIS],
      the OS[PM] will have already put the device in the D3 state."
      Unfortunately, there is no clear statement as to when to put
      a device in the D0 state. :-( Therefore, the patch executes the
      method calls as _PS3/_DIS and _SRS/_PS0. What is clear: "If the
      device is disabled, _SRS enables the device at the specified
      resources." (From the ACPI 3.0a Specification.)
      
      The patch fixes a problem with some IBM ThinkPads (at least the
      600E and the 600X) where the serial ports have a dedicated
      power source that needs to be brought up before the serial port
      can be used.  Without this patch, the serial port is enabled
      but has no power. (In the past, the tpctl utility had to be
      utilized to turn on the power, but support for this feature
      stopped with version 5.9 as it did not support the more recent
      kernel versions.)
      
      The error handlers that handle any errors that can occur during
      the power up/power down phases return the error codes to the
      caller directly.  Comments welcome! :-)
      
      No regressions were observed on hardware that does not require
      this patch.
      
      The patch is applied against 2.6.27.x.
      Signed-off-by: default avatarWitold Szczeponik <Witold.Szczeponik@gmx.net>
      Acked-by: default avatarZhao Yakui <yakui.zhao@intel.com>
      Signed-off-by: default avatarLen Brown <len.brown@intel.com>
      6328a574
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