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

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Date:	Tue, 10 Jun 2014 13:42:11 +0530
From:	Chander Kashyap <chander.kashyap@...aro.org>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:	Doug Anderson <dianders@...omium.org>,
	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 10 June 2014 04:08, Lorenzo Pieralisi <lorenzo.pieralisi@....com> wrote:
> 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.
>

Cpuidle is implemented for exynos5420, and is tested on chromebook.


> 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.

Yes thats true.
>
> 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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-- 
with warm regards,
Chander Kashyap
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