On 09/05/17 19:52, Phil Elwell wrote: > On 09/05/2017 19:14, Marc Zyngier wrote: >> On 09/05/17 19:08, Eric Anholt wrote: >>> Marc Zyngier <marc.zyng...@arm.com> writes: >>> >>>> On 09/05/17 17:59, Eric Anholt wrote: >>>>> Phil Elwell <p...@raspberrypi.org> 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 <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; >>>>>> } >>>>> >>>>> This is also the behavior that the standard arm64 spin-table method has, >>>>> which we unfortunately can't quite use. >>>> >>>> And why is that so? Why do you have to reinvent the wheel (and hide the >>>> cloned wheel in an interrupt controller driver)? >>>> >>>> That doesn't seem right to me. >>> >>> The armv8 stubs (firmware-supplied code in the low page that do the >>> spinning) do actually implement arm64's spin-table method. It's the >>> armv7 stubs that use these registers in the irqchip instead of plain >>> addresses in system memory. >> >> Let's put ARMv7 aside for the time being. If your firmware already >> implements spin-tables, why don't you simply use that at least on arm64? > > We do.
Obviously not the way it is intended if you have to duplicate the core architectural code in the interrupt controller driver, which couldn't care less. M. -- Jazz is not dead. It just smells funny...