Phil Elwell <[email protected]> writes: > 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 <[email protected]> > --- > 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; > }
This is also the behavior that the standard arm64 spin-table method has, which we unfortunately can't quite use. Acked-by: Eric Anholt <[email protected]>
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