• Gautham R. Shenoy's avatar
    powerpc/powernv/idle: Use Requested Level for restoring state on P9 DD1 · 22c6663d
    Gautham R. Shenoy authored
    On Power9 DD1 due to a hardware bug the Power-Saving Level Status
    field (PLS) of the PSSCR for a thread waking up from a deep state can
    under-report if some other thread in the core is in a shallow stop
    state. The scenario in which this can manifest is as follows:
       1) All the threads of the core are in deep stop.
       2) One of the threads is woken up. The PLS for this thread will
          correctly reflect that it is waking up from deep stop.
       3) The thread that has woken up now executes a shallow stop.
       4) When some other thread in the core is woken, its PLS will reflect
          the shallow stop state.
    Thus, the subsequent thread for which the PLS is under-reporting the
    wakeup state will not restore the hypervisor resources.
    Hence, on DD1 systems, use the Requested Level (RL) field as a
    workaround to restore the contents of the hypervisor resources on the
    wakeup from the stop state.
    Signed-off-by: default avatarGautham R. Shenoy <ego@linux.vnet.ibm.com>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
idle_book3s.S 22.5 KB