On the TC2 testchip, when all CPUs in a cluster enter standbywfi
and commit a power down request, the power controller will wait
for standbywfil2 coming from L2 cache controller to shut the
cluster down.
By the time all CPUs in a cluster commit a power down request
and enter wfi, the power controller cannot backtrack, or put it
another way, a CPU must not be allowed to complete execution
independently of the power controller, the only way for it to
resume properly must be upon wake-up IRQ pending and subsequent
reset triggered from the power controller.
Current MCPM back-end for TC2 disables the GIC CPU IF only when
power down is committed through the tc2_pm_suspend() method, that
makes sense since a suspended CPU is still online and can receive
interrupts whereas a hotplugged CPU, since it is offline,
migrated all IRQs and shutdown the per-CPU peripherals, hence
their PPIs.
The flaw with this reasoning is the following. If all CPUs in
a clusters are entering a power down state either through CPU
idle or CPU hotplug, when the last man successfully completes
the MCPM power down sequence (and executes wfi), power controller
waits for L2 wfi signal to quiesce the cluster and shut it down.
If, when all CPUs are sitting in wfi, an online CPU hotplugs back
in one of the CPUs in the cluster being shutdown, that CPU
receives an IPI that causes wfi to complete (since tc2_pm_down()
method does not disable the GIC CPU IF in that case - CPU being
hotplugged out, not idle) and the power controller will never see
the stanbywfil2 signal coming from L2 that is required for
shutdown to happen and the system deadlocks.
Further to this issue, kexec hotplugs secondary CPUs out during
kernel reload/restart.
Because kexec may (deliberately) trash the old kernel text, it is
not OK for CPUs to follow the MCPM soft reboot path, since
instructions after the WFI may have been replaced by kexec.
If tc2_pm_down() does not disable the GIC cpu interface, there is a
race between CPU powerdown in the old kernel and the IPI from the
new kernel that triggers secondary boot, particularly if the
powerdown is slow (due to L2 cache cleaning for example). If the
new kernel wins the race, the affected CPU(s) will not really be
reset and may execute garbage after the WFI.
The only solution to this problem consists in disabling the GIC
CPU IF on a CPU committed to power down regardless of the power
down entry method (CPU hotplug or CPU idle). This way, CPU wake-up
is under power controller control, which prevents unexpected wfi
exit caused by a pending IRQ.
This patch moves the GIC CPU IF disable call in the TC2 MCPM
implementation from the tc2_pm_suspend() method to the
tc2_pm_down() method to fix the mentioned race condition(s).
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Tested-by: Dave Martin <Dave.Martin@arm.com> (for kexec)
Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>
This branch contains ARM SoC related driver updates for v3.12. The
only thing this cycle are core PM updates and CPUidle support for
ARM's TC2 big.LITTLE development platform.
Conflicts:
One cleanup/reorg conflict with a new entry in
drivers/cpuidle/Makefile. Append the new entry after the existing
ones. A follow up patch for v3.12-rc will make the new entry conform
to the cleanup/reorg.
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Merge tag 'drivers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc
Pull ARM SoC driver update from Kevin Hilman:
"This contains the ARM SoC related driver updates for v3.12. The only
thing this cycle are core PM updates and CPUidle support for ARM's TC2
big.LITTLE development platform"
* tag 'drivers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc:
cpuidle: big.LITTLE: vexpress-TC2 CPU idle driver
ARM: vexpress: tc2: disable GIC CPU IF in tc2_pm_suspend
drivers: irq-chip: irq-gic: introduce gic_cpu_if_down()
To prevent cores from exiting wfi when they are about to be shut down
the GIC CPU IF must be disabled so that the GIC CPU IF IRQ output line
is not asserted to the cores. wfi completion must be prevented since,
in absence of coordinating HW logic, if the power controller receives
a standbywfi signal but in the meantime the processor restarts executing
owing to a pending IRQ, the core might be reset when running in a
non-quiescent state (eg with pending load/store transactions)
Raw GIC distributor IRQ signals are routed to the power controller, that
is capable of taking core out of reset on pending IRQs even if their GIC
CPU IF is disabled, thus keeping the normal wfi behaviour.
GIC CPU IF is restored upon CPU wake-up by the respective MCPM API
consumers (ie CPU idle driver and suspend to RAM thread).
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Olof Johansson <olof@lixom.net>
If CONFIG_FRAME_POINTER=y we get the following error:
arch/arm/mach-vexpress/tc2_pm.c: In function 'tc2_pm_down':
arch/arm/mach-vexpress/tc2_pm.c:200:1: error: fp cannot be used in asm here
Let's fix that by explicitly preserving r11 on the stack and removing it
from the clobber list.
Reported-by: Russell King <rmk+kernel@arm.linux.org.uk>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>
Similar to power_down(), except that for a suspend, the firmware
mailbox address has to be set prior entering low power mode.
The residency argument is not used yet, so the last man always shuts
down the cluster for now.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Pawel Moll <pawel.moll@arm.com>
This is the MCPM backend for the Virtual Express A15x2 A7x3 CoreTile
aka TC2. This provides cluster management for SMP secondary boot and
CPU hotplug.
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Pawel Moll <pawel.moll@arm.com>
Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
[PM: made it drive SCC registers directly and provide base for SPC]
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Lorenzo Pieralisi
Linus Torvalds
Nicolas Pitre
Nicolas Pitre