linux-kernel - Re: [PATCH] ARM: EXYNOS: mcpm: Don't rely on firmware's secondary_cpu

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Date:	Mon, 9 Jun 2014 23:38:31 +0100
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Kukjin Kim <kgene.kim@...sung.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Abhilash Kesavan <a.kesavan@...sung.com>,
	Andrew Bresticker <abrestic@...omium.org>,
	Inderpal Singh <inderpal.s@...sung.com>,
	Thomas Abraham <thomas.ab@...sung.com>,
	"olof@...om.net" <olof@...om.net>,
	Tushar Behera <trblinux@...il.com>,
	Kevin Hilman <khilman@...aro.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: EXYNOS: mcpm: Don't rely on firmware's
 secondary_cpu_start

On Mon, Jun 09, 2014 at 06:03:31PM +0100, Doug Anderson wrote:

[...]

> Cold boot and resume from suspend are detected via various special
> flags in various special locations.  Resume from suspend looks at
> INFORM1 (0x10048004) for flags.  This register is 0 during a cold boot
> and has special values set by the kernel at resume time.
> 
> It also looks as if some code looks at 0x10040900 (PMU_SPARE0) to help
> tell initial cold boot and secondary CPU bringup.

Ok, thanks a lot. It looks like firmware paths should be ready to
detect cold vs warm boot, and hopefully do not rely on a specific
MPIDR to come up first out of power states.

> > I am asking to check if on this platform CPUidle (where the notion of
> > primary CPU disappears) has a chance to run properly.
> 
> I believe it should be possible, but we don't have CPUidle implemented
> in our current system.  Abhilash may be able to comment more.

I am interested in more insights, that's very helpful thanks.

> > Probably CPUidle won't attain idle states where IRAM content is lost, but I
> > am still worried about the primary vs secondaries firmware boot behaviour.
> 
> I don't think iRAM can be turned off for CPUidle.

It might be added a system state but I doubt that too and if you are
relying on registers for jump addresses that's not even a problem in
the first place.

> > What happens on reboot from suspend to RAM (or to put it differently,
> > what does secure firmware do on reboot from suspend to RAM - in
> > particular how is the "jump" address to bootloader/kernel set ?)
> 
> Should be described above now.

Thank you very much.

Lorenzo

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