On Fri, Aug 26, 2016 at 12:09:38PM +0200, Thomas Gleixner wrote:

On Fri, 26 Aug 2016, Will Deacon wrote:

quoted

On Wed, Aug 17, 2016 at 01:50:25PM +0100, James Morse wrote:

quoted

disable_nonboot_cpus() assumes that the lowest numbered online CPU is
the boot CPU, and that this is the correct CPU to run any power
management code on.

On x86 this is always correct, as CPU0 cannot (easily) by taken offline.

On arm64 CPU0 can be taken offline. For hibernate/resume this means we
may hibernate on a CPU other than CPU0. If the system is rebooted with
kexec 'CPU0' will be assigned to a different physical CPU. This
complicates hibernate/resume as now we can't trust the CPU numbers.
Arch code can find the correct physical CPU, and ensure it is online
before resume from hibernate begins, but also needs to influence
disable_nonboot_cpus()s choice of CPU.

Rename disable_nonboot_cpus() as freeze_secondary_cpus() and add an
argument indicating which CPU should be left standing. Follow the logic
in migrate_to_reboot_cpu() to use the lowest numbered online CPU if the
requested CPU is not online.
Add disable_nonboot_cpus() as an inline function that has the existing
behaviour.

Signed-off-by: James Morse <james.morse@arm.com>
Cc: Rafael J. Wysocki <redacted>
---
An alternative is to provide two functions calling a common function,
but this would mean spilling the cpu_maps_update_begin() into these two.

 include/linux/cpu.h | 6 +++++-
 kernel/cpu.c        | 9 +++++----
 2 files changed, 10 insertions(+), 5 deletions(-)

Thomas, does this look ok to you? If so, would you prefer to merge this
series via -tip, or have us take this one via the arm64 tree?

You can take it via ARM64. It's not conflicting with the stuff I have in the
pipeline.

Reviewed-by: Thomas Gleixner <redacted>

Brill, thanks Thomas.

Will