linux-kernel - Re: [RESEND PATCH 2/6] soc: Mediatek: Add SCPSYS CPU power domain driver

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Date:	Fri, 24 Jul 2015 07:50:38 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Scott Shu <scott.shu@...iatek.com>
Cc:	yingjoe.chen@...iatek.com, robh+dt@...nel.org,
	matthias.bgg@...il.com, linux@....linux.org.uk,
	rchintakuntla@...ium.com, lorenzo.pieralisi@....com,
	marc.ceeeee@...il.com, heiko@...ech.de, catalin.marinas@....com,
	arnd@...db.de, galak@...eaurora.org, srv_wsdupstream@...iatek.com,
	linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, loda.chou@...iatek.com,
	jades.shih@...iatek.com, scott.shu@...il.com
Subject: Re: [RESEND PATCH 2/6] soc: Mediatek: Add SCPSYS CPU power domain
 driver

On Fri, Jul 24, 2015 at 10:02:03AM +0800, Scott Shu wrote:
> On Tue, 2015-06-23 at 07:53 +0200, Sascha Hauer wrote:
> > Hi Scott,
> > 
> > On Fri, Jun 19, 2015 at 02:01:17AM +0800, Scott Shu wrote:
> > > This adds a CPU power domain driver for the Mediatek SCPSYS unit on
> > > MT6580.
> > 
> > This seems to be support for the very same hardware as I am posting
> > here:
> > 
> > https://lkml.org/lkml/2015/6/22/41
> > 
> > We should consolidate this.
> > 
> > My driver is currently handles all power domains except the CPUs while
> > yours handles only the CPUs.
> > I currently haven't looked whether CPUs can just be part of a power
> > domain aswell, but if that works this would probably be the way to go.
> > 
> > Sascha
> > 
> > 
> Hi Sascga,
> 
> We had posted new patch set in following link, but still keep our
> original framework.
> http://lists.infradead.org/pipermail/linux-mediatek/2015-July/001498.html
> 
> As we mentioned in the new email thread, the SMP operations (smp_boot_secondary)
> will be executed before registering the scpsys_drv driver, so the CPUs power
> domain is controlled on arch/arm/mach-$(MACHINE) directory. 
> 
> Please kindly provide your comments and suggestion. Thank you very much.

I think that instead of explaining why have to duplicate the code you
should rather search for ways how the code can be shared. Yes, we'll
need a second (early) entry point to the driver. Maybe we even have to
create the shared code which is then called from the driver and your
early architecture code.
You'll probably have to do this separation between early code and
regular driver code in your driver anyway, since I bet the MT6580 also
has some power domains which shall be controlled by the regular Linux
power domain code later. Also we probably could control the CPU power
domains for the MT8173 in the SCPSYS driver aswell, we just don't have
to because we use PSCI there. You see we are approaching the same
problem from two different corners. Let's find a way to share the code.

Sascha

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