On Wed, May 10 2017 at 7:02:44 pm BST, Eric Anholt <e...@anholt.net> wrote: > Florian Fainelli <f.faine...@gmail.com> writes: > >> On 05/10/2017 03:31 AM, Phil Elwell wrote: >>> On 10/05/2017 11:09, Marc Zyngier wrote: >>>> On 10/05/17 10:05, Phil Elwell wrote: >>>>> On 10/05/2017 09:55, Marc Zyngier wrote: >>>>>> On Wed, May 10 2017 at 9:27:10 am BST, Phil Elwell >>>>>> <p...@raspberrypi.org> wrote: >>>>>>> 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. >>>>>> >>>>>> Well, I'm far from being perfect. If I had noticed it, I'd have NACKed >>>>>> it. >>>>>> >>>>>>> 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? >>>>>> >>>>>> On its own, no. I'm just not keen on adding more unrelated stuff to this >>>>>> file, so let's start with dealing with the original bug, and you can >>>>>> then add this fix on top. >>>>> >>>>> That's an interesting use of the word "bug". From Wikipedia: >>>>> >>>>> "A software bug is an error, flaw, failure or fault in a computer >>>>> program or >>>>> system that causes it to produce an incorrect or unexpected result, or to >>>>> behave in unintended ways." >>>> >>>> Whatever. Should I call it "pile of crap dumped in unsuitable locations" >>>> instead? What does Wikipedia says about it? >>>> >>>>> Although your concerns are valid, the faults you are objecting to >>>>> are not causing >>>>> a malfunction of any kind. If we were to update the RPi firmware >>>>> before this >>>>> patch was merged then upstream users would be left with one wheel >>>>> on their wagon. >>>> >>>> And that'd be your problem, not mine. Look, you can argue around this >>>> all day, or you can fix this mess. Your choice. >>> >>> Is that the opinion of all here? >> >> The choice of word here got largely out of the original topic and I >> surely did eat a ton of popcorn here. There are two things that need >> fixing, and the time line and process for fixing these is clear: >> >> - your bugfix (Phil) is something that should be applied now, and >> backported to -stable trees once the fix hits the irqchip tree (or Linus') >> >> - relocating the code that does the secondary boot out of >> drivers/irqchip/ into arch/arm/mach-bcm/ needs to happen (Marc), and >> this is 4.13 material, there is no urgency in doing this *right now*, >> but it needs to happen >> >> Does that work for everyone? > > Agreed. This patch, which we'll want to go to -stable, should clearly > go in first. Marc's patch can go in after, since it's not a -stable > candidate. > > Thomas, could you add the cc to stable when picking this patch?
So, for the record, I'm clearly NAKing this patch. Thomas or Jason can pick it if they want to, I definitely won't. M. -- Jazz is not dead, it just smell funny.