linux-kernel - Re: [RFC PATCH 5/5] arm64: qcom: add cpu operations

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Date:	Tue, 14 Apr 2015 22:51:40 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Mark Rutland <mark.rutland@....com>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"arm@...nel.org" <arm@...nel.org>,
	Abhimanyu Kapur <abhimany@...eaurora.org>
Subject: Re: [RFC PATCH 5/5] arm64: qcom: add cpu operations

On Tuesday 14 April 2015 17:29:53 Mark Rutland wrote:
> 
> > +static int msm_cpu_boot(unsigned int cpu)
> > +{
> > +       int ret = 0;
> > +
> > +       if (per_cpu(cold_boot_done, cpu) == false) {
> > +               ret = msm_unclamp_secondary_arm_cpu(cpu);
> > +               if (ret)
> > +                       return ret;
> > +               per_cpu(cold_boot_done, cpu) = true;
> > +       }
> > +       return secondary_pen_release(cpu);
> > +}
> 
> Ah, so cold_boot_done is for pseudo-hotplug. Absolute NAK to that.
> 
> The only thing this gives you over spin-table is one-time powering up of
> the CPUs that can be performed prior to entry to Linux. If you do that,
> you can trivially share the spin-table code by setting each CPU's
> enable-method to "spin-table".
> 
> That won't give you cpuidle or actual hotplug. For those you'll need
> PSCI.

Maybe a way out for the broken firmware is to have a custom boot wrapper
that gets distributed separately and that uses the normal spin-table
API. We've done similar things on arch/arm/mach-sunxi for boot loaders
that are just too different from what we expect.

Once someone implements a proper loader, they could skip that extra
wrapper.

	Arnd
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