linux-kernel - Re: [PATCH] ARM: bcm2836: Send event when onlining other cores

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Date:   Mon, 14 Aug 2017 19:11:35 +0200 (CEST)
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Eric Anholt <eric@...olt.net>,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     Phil Elwell <phil@...pberrypi.org>,
        Scott Branden <sbranden@...adcom.com>,
        Ray Jui <rjui@...adcom.com>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH] ARM: bcm2836: Send event when onlining other cores

Hi Florian,

> Florian Fainelli <f.fainelli@...il.com> hat am 14. August 2017 um 18:25 geschrieben:
> 
> 
> 
> 
> On 08/08/2017 04:04 AM, Phil Elwell wrote:
> > Secondary cores should 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, and
> > the "sev" instruction sends a wakeup event to the other cores.
> > 
> > Add an "sev" (and a memory barrier) to bcm2836_boot_secondary, the
> > function that wakes the waiting cores during booting. This is required
> > if the secondary cores are sitting in "wfe", and harmless if not.
> 
> Eric, should I just pick this up for the upcoming ARM SoC pull requests
> that I am preparing, or do you have more changes aside from the two tags
> I already merged?

this patch depends on series "ARM: bcm2836: Move SMP startup code to arch/arm".

I didn't had the time to test Phil's patch in all relevant cases. But i could at least prepare a branch with my changes with the acks.

Stefan

> 
> Thanks!
> 
> > 
> > Signed-off-by: Phil Elwell <phil@...pberrypi.org>
> > ---
> >  arch/arm/mach-bcm/platsmp.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/arm/mach-bcm/platsmp.c b/arch/arm/mach-bcm/platsmp.c
> > index 3fa1a99..7811160 100644
> > --- a/arch/arm/mach-bcm/platsmp.c
> > +++ b/arch/arm/mach-bcm/platsmp.c
> > @@ -312,6 +312,9 @@ static int bcm2836_boot_secondary(unsigned int cpu, struct task_struct *idle)
> >  	writel(virt_to_phys(secondary_startup),
> >  	       intc_base + LOCAL_MAILBOX3_SET0 + 16 * cpu);
> >  
> > +	dsb(sy);
> > +	sev();
> > +
> >  	iounmap(intc_base);
> >  
> >  	return 0;
> > 
> 
> -- 
> Florian