Messages in this thread | | | Subject | Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores | From | Phil Elwell <> | Date | Tue, 9 May 2017 19:52:08 +0100 |
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On 09/05/2017 19:14, Marc Zyngier wrote: > On 09/05/17 19:08, Eric Anholt wrote: >> Marc Zyngier <marc.zyngier@arm.com> writes: >> >>> On 09/05/17 17:59, Eric Anholt wrote: >>>> Phil Elwell <phil@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 <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; >>>>> } >>>> >>>> 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.
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