• Dave Martin's avatar
    ARM: vexpress/TC2: Implement MCPM power_down_finish() · 33cb667a
    Dave Martin authored
    This patch implements the power_down_finish() method for TC2, to
    enable the kernel to confirm when CPUs are safely powered down.
    
    The information required for determining when a CPU is parked
    cannot be obtained from any single place, so a few sources of
    information must be combined:
    
      * mcpm_cpu_power_down() must be pending for the CPU, so that we
        don't get confused by false STANDBYWFI positives arising from
        CPUidle.  This is detected by waiting for the tc2_pm use count
        for the target CPU to reach 0.
    
      * Either the SPC must report that the CPU has asserted
        STANDBYWFI, or the TC2 tile's reset control logic must be
        holding the CPU in reset.
    
        Just checking for STANDBYWFI is not sufficient, because this
        signal is not latched when the the cluster is clamped off and
        powered down: the relevant status bits just drop to zero.  This
        means that STANDBYWFI status cannot be used for reliable
        detection of the last CPU in a cluster reaching WFI.
    
    This patch is required in order for kexec to work with MCPM on TC2.
    
    MCPM code was changed in commit 0de0d646 ('ARM: 7848/1: mcpm:
    Implement cpu_kill() to synchronise on powerdown'), and since then it
    will hit a WARN_ON_ONCE() due to power_down_finish not being implemented
    on the TC2 platform.
    Signed-off-by: default avatarDave Martin <Dave.Martin@arm.com>
    Acked-by: default avatarPawel Moll <pawel.moll@arm.com>
    Reviewed-by: default avatarNicolas Pitre <nico@linaro.org>
    Signed-off-by: default avatarOlof Johansson <olof@lixom.net>
    33cb667a
tc2_pm.c 9.75 KB