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 <p...@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
