linux-kernel - Re: [PATCH v2 02/31] arm64: Kernel booting and initialisation

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Date:	Fri, 24 Aug 2012 10:50:12 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Tony Lindgren <tony@...mide.com>
Cc:	"Shilimkar, Santosh" <santosh.shilimkar@...com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Will Deacon <Will.Deacon@....com>
Subject: Re: [PATCH v2 02/31] arm64: Kernel booting and initialisation

On Fri, Aug 17, 2012 at 02:13:59PM +0100, Tony Lindgren wrote:
> * Shilimkar, Santosh <santosh.shilimkar@...com> [120817 03:11]:
> > On Fri, Aug 17, 2012 at 3:35 PM, Catalin Marinas
> > <catalin.marinas@....com> wrote:
> > >
> > > On Fri, Aug 17, 2012 at 10:41:10AM +0100, Santosh Shilimkar wrote:
> > > >
> > > > So you expect all the secondary CPUs to be in wakeup state and probably
> > > > looping in WFE for a signal from kernel to boot. There is one issue
> > > > with this requirement though. For large CPU system, you need to reset
> > > > all the CPUs and hit this waiting loop. This will lead to large inrush
> > > > current need at bootup which may be not be supported. To avoid this
> > > > issue, secondary CPUs are kept in OFF state and then they are woken
> > > > up from kernel one by one whenever they need to be brought into the
> > > > system. This requirement should be considered.
> > >
> > > I agree, this part will be extended. That's one method that we currently
> > > support and suitable to the model.
> > >
> > > The better method is the SMC standardisation that Charles Garcia-Tobin
> > > has written (to be made available soon) and was presented at the last
> > > Linaro Connect in HK. Given that the CPU power is usually controlled by
> > > the secure side, we'll ask for an SMC to be issued for waking up
> > > secondary CPUs, so it's up to the secure firmware to write the correct
> > > hardware registers.
> > >
> > Thanks for the information. SMC standardization would indeed help
> > to overcome some of these. Will wait for that information before
> > next set of questions.
> 
> Yes please. If the SMC is not standardized for most calls at least,
> we'll end up with a horrible mess of SoC specific calls like we
> currently have. Related to that, the virtualization calls should be
> also standardized so we don't end up with multiple different hypervisors
> with different calls.

The Power State Coordination Interface initial proposal has been
published here:

http://infocenter.arm.com/help/topic/com.arm.doc.den0022a/index.html

(as with other ARM documents, they are public but free registration
required).

-- 
Catalin
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