Messages in this thread | | | Subject | Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores | From | Phil Elwell <> | Date | Tue, 9 May 2017 20:02:29 +0100 |
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On 09/05/2017 19:53, Marc Zyngier wrote: > 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.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. > > 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.
If we were using this method on arm64 then the other cores would not start up because armstub8.S has always included a wfe. Nothing in the commit mentions arm64 - this is an ARCH=arm fix.
Phil
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