1. 03 2月, 2007 38 次提交
  2. 27 1月, 2007 1 次提交
    • I
      [PATCH] ACPI: fix cpufreq regression · e4233dec
      Ingo Molnar 提交于
      Recently cpufreq support on my laptop (Lenovo T60) broke completely: when
      it's plugged into AC it would never go higher than 1 GHz - neither 1.3 GHz
      nor 1.83 GHz is possible - no matter which governor (userspace, speed or
      ondemand) is used.
      
      After some cpufreq debugging i tracked the regression back to the following
      (totally correct) bug-fix commit:
      
         commit 0916bd3e
         Author: Dave Jones <davej@redhat.com>
         Date:   Wed Nov 22 20:42:01 2006 -0500
      
          [PATCH] Correct bound checking from the value returned from _PPC method.
      
      This bugfix, which makes other laptops work, made a previously hidden
      (BIOS) bug visible on my laptop.
      
      The bug is the following: if the _PPC (Performance Present Capabilities)
      optional ACPI object is queried /after/ bootup then the BIOS reports an
      incorrect value of '2'.
      
      My laptop (Lenovo T60) has the following performance states supported:
      
         0: 1833000
         1: 1333000
         2: 1000000
      
      Per ACPI specification, a _PPC value of '0' means that all 3 performance
      states are usable.  A _PPC value of '1' means states 1 ..  2 are usable, a
      value of '2' means only state '2' (slowest) is usable.
      
      now, the _PPC object is optional, and it also comes with notification.
      Furthermore, when a CPU object is initialized, the _PPC object is
      initialized as well.  So the following evaluation of the _PPC object is
      superfluous:
      
       [<c028ba5f>] acpi_processor_get_platform_limit+0xa1/0xaf
       [<c028c040>] acpi_processor_register_performance+0x3b9/0x3ef
       [<c0111a85>] acpi_cpufreq_cpu_init+0xb7/0x596
       [<c03dab74>] cpufreq_add_dev+0x160/0x4a8
       [<c02bed90>] sysdev_driver_register+0x5a/0xa0
       [<c03d9c4c>] cpufreq_register_driver+0xb4/0x176
       [<c068ac08>] acpi_cpufreq_init+0xe5/0xeb
       [<c010056e>] init+0x14f/0x3dd
      
      And this is the point where my laptop's BIOS returns the incorrect value of
      '2'.  Note that it has not sent any notification event, so the value is
      probably not really intentional (possibly spurious), and Windows likely
      doesnt query it after bootup either.  Maybe the value is kept at '2'
      normally, and is only set to the real value when a true asynchronous event
      (such as AC plug event, battery switch, etc.) occurs.
      
      So i /think/ this is a grey area of the ACPI spec: per the letter of the
      spec the _PPC value only changes when notified, so there's no reason to
      query it after the system has booted up.  So in my opinion the best (and
      most compatible) strategy would be to do the change below, and to not
      evaluate the _PPC object in the acpi_processor_get_performance_info() call,
      but only evaluate it if _PPC is present during CPU object init, or if it's
      notified during an asynchronous event.  This change is more permissive than
      the previous logic, so it definitely shouldnt break any existing system.
      
      This also happens to fix my laptop, which is merrily chugging along at
      1.83 GHz now. Yay!
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      Cc: Dave Jones <davej@redhat.com>
      Acked-by: NLen Brown <lenb@kernel.org>
      Signed-off-by: NAndrew Morton <akpm@osdl.org>
      Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      e4233dec
  3. 23 1月, 2007 1 次提交