linux-kernel - Re: [PATCH 1/3] arm: ls1: add CPU hotplug platform support

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Date:	Fri, 26 Sep 2014 13:46:14 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Chenhui Zhao <chenhui.zhao@...escale.com>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Zhuoyu.Zhang@...escale.com" <Zhuoyu.Zhang@...escale.com>,
	"Jason.Jin@...escale.com" <Jason.Jin@...escale.com>,
	"leoli@...escale.com" <leoli@...escale.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/3] arm: ls1: add CPU hotplug platform support

On Fri, Sep 26, 2014 at 01:20:04PM +0100, Russell King - ARM Linux wrote:
> On Fri, Sep 26, 2014 at 07:25:01PM +0800, Chenhui Zhao wrote:
> > +static inline void ls1_do_lowpower(unsigned int cpu, int *spurious)
> > +{
> > +	/*
> > +	 * there is no power-control hardware on this platform, so all
> > +	 * we can do is put the core into WFI; this is safe as the calling
> > +	 * code will have already disabled interrupts
> > +	 */
> > +	for (;;) {
> > +		wfi();
> > +
> > +		if (pen_release == cpu_logical_map(cpu)) {
> > +			/*OK, proper wakeup, we're done*/
> > +			break;
> > +		}
> > +
> > +		/*
> > +		 * Getting here, means that we have come out of WFI without
> > +		 * having been woken up - this shouldn't happen
> > +		 *
> > +		 * Just note it happening - when we're woken, we can report
> > +		 * its occurrence.
> > +		 */
> > +		(*spurious)++;
> > +	}
> > +}
> 
> This is pretty much unacceptable - this breaks kexec(), and suspend
> support because your secondary CPUs aren't really sleeping, they're
> sitting in a loop doing nothing.

Agreed.

This looks to be a carbon copy of the vexpress pseudo-hotplug in
arch/arm/mach-vexpress/hotplug.c, which is obviously broken in the way
you describe above. Perhaps we should go about ripping that out?

Mark.
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