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

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Date:	Wed, 15 Apr 2015 15:46:32 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	Kumar Gala <galak@...eaurora.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 Tue, Apr 14, 2015 at 10:51:40PM +0200, Arnd Bergmann wrote:
> 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.

As a starting point, we actually have one that can do both spin table
and PSCI ;) (three-clause BSD license):

git://git.kernel.org/pub/scm/linux/kernel/git/mark/boot-wrapper-aarch64.git

Its primary goal is to create an ELF file that can be loaded on a
software model but there isn't anything that prevents you from
generating a kernel Image-like header.

-- 
Catalin
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