Re: [PATCH] ARM: EXYNOS: mcpm: Don't rely on firmware's secondary_cpu_start

[Lorenzo Pieralisi]

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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/