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

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Date:	Fri, 18 Sep 2015 14:38:39 +0000
From:	Shenwei Wang <Shenwei.Wang@...escale.com>
To:	Shawn Guo <shawnguo@...nel.org>
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



> -----Original Message-----
> From: Shawn Guo [mailto:shawnguo@...nel.org]
> Sent: 2015年9月18日 9:15
> To: Wang Shenwei-B38339
> Cc: jason@...edaemon.net; Huang Yongcai-B20788;
> linux-kernel@...r.kernel.org; kernel@...gutronix.de; Sudeep Holla;
> tglx@...utronix.de; shawn.guo@...aro.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.

The current PSCI support in uboot is not complete. It can now support cpuidle, shutdown, 
and reset. But to support system suspend, there would be a lot more tasks. For example,
even the current wakeup source management codes will have to move into the firmware 
too. It is not a short time task. Please continue to consider this platform dependent implementation
first, meanwhile, we will start to migrate the solution to PSCI. However it will take some time.

Thanks,
Shenwei

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