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ARM: vexpress/TC2: Implement MCPM power_down_finish()
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 0de0d64 ('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 <[email protected]> Acked-by: Pawel Moll <[email protected]> Reviewed-by: Nicolas Pitre <[email protected]> Signed-off-by: Olof Johansson <[email protected]>
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