• Preeti U Murthy's avatar
    PM / cpuidle: System resume hang fix with cpuidle · 8651f97b
    Preeti U Murthy authored
    On certain bios, resume hangs if cpus are allowed to enter idle states
    during suspend [1].
    This was fixed in apci idle driver [2].But intel_idle driver does not
    have this fix. Thus instead of replicating the fix in both the idle
    drivers, or in more platform specific idle drivers if needed, the
    more general cpuidle infrastructure could handle this.
    A suspend callback in cpuidle_driver could handle this fix. But
    a cpuidle_driver provides only basic functionalities like platform idle
    state detection capability and mechanisms to support entry and exit
    into CPU idle states. All other cpuidle functions are found in the
    cpuidle generic infrastructure for good reason that all cpuidle
    drivers, irrepective of their platforms will support these functions.
    One option therefore would be to register a suspend callback in cpuidle
    which handles this fix. This could be called through a PM_SUSPEND_PREPARE
    notifier. But this is too generic a notfier for a driver to handle.
    Also, ideally the job of cpuidle is not to handle side effects of suspend.
    It should expose the interfaces which "handle cpuidle 'during' suspend"
    or any other operation, which the subsystems call during that respective
    The fix demands that during suspend, no cpus should be allowed to enter
    deep C-states. The interface cpuidle_uninstall_idle_handler() in cpuidle
    ensures that. Not just that it also kicks all the cpus which are already
    in idle out of their idle states which was being done during cpu hotplug
    through a CPU_DYING_FROZEN callbacks.
    Now the question arises about when during suspend should
    cpuidle_uninstall_idle_handler() be called. Since we are dealing with
    drivers it seems best to call this function during dpm_suspend().
    Delaying the call till dpm_suspend_noirq() does no harm, as long as it is
    before cpu_hotplug_begin() to avoid race conditions with cpu hotpulg
    operations. In dpm_suspend_noirq(), it would be wise to place this call
    before suspend_device_irqs() to avoid ugly interactions with the same.
    Ananlogously, during resume.
    [1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/674075.
    [2] http://marc.info/?l=linux-pm&m=133958534231884&w=2
    Reported-and-tested-by: default avatarDave Hansen <dave@linux.vnet.ibm.com>
    Signed-off-by: default avatarPreeti U Murthy <preeti@linux.vnet.ibm.com>
    Reviewed-by: default avatarSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    Signed-off-by: default avatarRafael J. Wysocki <rjw@sisk.pl>