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[PATCH] irq_bcm2836: Send event when onlining sleeping cores

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In order to reduce power consumption and bus traffic, it is sensible
for secondary cores to enter a low-power idle state when waiting to
be started. The wfe instruction causes a core to wait until an event
or interrupt arrives before continuing to the next instruction.
The sev instruction sends a wakeup event to the other cores, so call
it from bcm2836_smp_boot_secondary, the function that wakes up the
waiting cores during booting.

It is harmless to use this patch without the corresponding change
adding wfe to the ARMv7/ARMv8-32 stubs, but if the stubs are updated
and this patch is not applied then the other cores will sleep forever.

See: https://github.com/raspberrypi/linux/issues/1989

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
---
 drivers/irqchip/irq-bcm2836.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/irqchip/irq-bcm2836.c b/drivers/irqchip/irq-bcm2836.c
index e10597c..6dccdf9 100644
--- a/drivers/irqchip/irq-bcm2836.c
+++ b/drivers/irqchip/irq-bcm2836.c
@@ -248,6 +248,9 @@ static int __init bcm2836_smp_boot_secondary(unsigned int cpu,
 	writel(secondary_startup_phys,
 	       intc.base + LOCAL_MAILBOX3_SET0 + 16 * cpu);
 
+	dsb(sy); /* Ensure write has completed before waking the other CPUs */
+	sev();
+
 	return 0;
 }
 
-- 
1.9.1

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[PATCH] irq_bcm2836: Send event when onlining sleeping cores Phil Elwell <phil@raspberrypi.org> - 2017-05-09 11:00 +0200
  Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Eric Anholt <eric@anholt.net> - 2017-05-09 19:00 +0200
    Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Marc Zyngier <marc.zyngier@arm.com> - 2017-05-09 19:20 +0200
      Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Eric Anholt <eric@anholt.net> - 2017-05-09 20:10 +0200
        Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Marc Zyngier <marc.zyngier@arm.com> - 2017-05-09 20:20 +0200
          Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Phil Elwell <phil@raspberrypi.org> - 2017-05-09 20:50 +0200
            Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Marc Zyngier <marc.zyngier@arm.com> - 2017-05-09 21:00 +0200
              Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Phil Elwell <phil@raspberrypi.org> - 2017-05-09 21:10 +0200
                Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Marc Zyngier <marc.zyngier@arm.com> - 2017-05-10 09:50 +0200
                Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Phil Elwell <phil@raspberrypi.org> - 2017-05-10 10:30 +0200
                Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Marc Zyngier <marc.zyngier@arm.com> - 2017-05-10 11:00 +0200
                Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Phil Elwell <phil@raspberrypi.org> - 2017-05-10 11:10 +0200
                Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Marc Zyngier <marc.zyngier@arm.com> - 2017-05-10 12:10 +0200
                Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Phil Elwell <phil@raspberrypi.org> - 2017-05-10 12:40 +0200
                Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Florian Fainelli <f.fainelli@gmail.com> - 2017-05-10 18:30 +0200
                Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Marc Zyngier <marc.zyngier@arm.com> - 2017-05-10 19:20 +0200
                Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Florian Fainelli <f.fainelli@gmail.com> - 2017-05-10 20:00 +0200
                Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Eric Anholt <eric@anholt.net> - 2017-05-10 20:10 +0200
                Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores Marc Zyngier <marc.zyngier@arm.com> - 2017-05-10 20:30 +0200

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