On 10/05/2017 08:42, Marc Zyngier wrote: > On 09/05/17 20:02, Phil Elwell wrote: >> 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.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. >> >> 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. > > Thanks for the clarification, which you could have added to the commit > message. > > The question still remains: why do we have CPU bring-up code in an > interrupt controller, instead of having it in the architecture code? > > The RPi-2 is the *only* platform to have its SMP bringup code outside of > arch/arm, so the first course of action would be to move that code where > it belongs.
You were CC'd on the commit (41f4988cc287e5f836d3f6620c9f900bc9b560e9) that introduced bcm2836_smp_boot_secondary - it seems strange to start objecting now. Yes, I think it is odd that it didn't go into arch/arm/mach-bcm, but in the interests of making changes in small, independent steps, do you have a problem with this commit? Phil