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 0de0d64675 ('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: Dave Martin <Dave.Martin@arm.com>
Acked-by: Pawel Moll <pawel.moll@arm.com>
Reviewed-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>
33cb667a00