linux-kernel - Re: [PATCH v8 2/2] ARM: imx: support suspend states on imx7D

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Date:	Fri, 18 Sep 2015 22:15:24 +0800
From:	Shawn Guo <shawnguo@...nel.org>
To:	Shenwei Wang <Shenwei.Wang@...escale.com>
Cc:	"jason@...edaemon.net" <jason@...edaemon.net>,
	Huang Anson <Anson.Huang@...escale.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	Sudeep Holla <sudeep.holla@....com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v8 2/2] ARM: imx: support suspend states on imx7D

On Tue, Sep 08, 2015 at 03:01:07PM +0000, Shenwei Wang wrote:
> > >  arch/arm/mach-imx/Kconfig        |   1 +
> > >  arch/arm/mach-imx/Makefile       |   2 +
> > >  arch/arm/mach-imx/common.h       |   4 +
> > >  arch/arm/mach-imx/pm-imx7.c      | 917
> > +++++++++++++++++++++++++++++++++++++++
> > >  arch/arm/mach-imx/suspend-imx7.S | 529 ++++++++++++++++++++++
> > >  5 files changed, 1453 insertions(+)
> > 
> > 1453 lines addition to kernel only for i.MX7D suspend support.  Yes, this is the
> > way we support suspend on i.MX6, but that's enough, and we have to stop this
> > somewhere.  I would ask you to take Sudeep's comment and adopt PSCI for
> > i.MX7D power management.
> 
> According to PSCI spec, a supervisory software must be implemented under either
> HVC(EL2) or SMC(EL3) privilege level. I agree that, with this idea, we could finally move 
> these 1453 lines of codes from kernel into a platform specific firmware. The problem
> is we don't have the firmware so far, and we haven't even had a plan to enable the
> hypervisor or secure software on this platform. Because low power consumption is
> the key feature of this i.MX7D platform, please continue to consider the current 
> implementation and get this feature supported first. 

Can't U-Boot be considered as a firmware to implement PSCI?  I have seen
an initial ARMv7 PSCI core support for U-Boot added by Marc Zyngier.

Shawn

[1] http://lists.denx.de/pipermail/u-boot/2013-December/168655.html
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