linux-kernel - Re: [PATCH 01/11] ARM: vexpress: use ARM_CPU

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Date:	Sat, 14 Feb 2015 07:03:46 +0800 (HKT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Liviu Dudau <Liviu.Dudau@....com>
cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"arm@...nel.org" <arm@...nel.org>,
	Kevin Hilman <khilman@...aro.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>
Subject: Re: [PATCH 01/11] ARM: vexpress: use ARM_CPU_SUSPEND if needed

On Fri, 13 Feb 2015, Liviu Dudau wrote:

> On Fri, Feb 13, 2015 at 11:16:12AM +0000, Russell King - ARM Linux wrote:
> > On Fri, Feb 13, 2015 at 11:01:52AM +0000, Liviu Dudau wrote:
> > > On Fri, Feb 13, 2015 at 10:57:53AM +0000, Russell King - ARM Linux wrote:
> > > > On Fri, Feb 13, 2015 at 10:37:16AM +0000, Liviu Dudau wrote:
> > > > > On Thu, Feb 12, 2015 at 07:42:33PM +0000, Arnd Bergmann wrote:
> > > > > > The vexpress tc2 power management code calls mcpm_loopback, which
> > > > > > is only available if ARM_CPU_SUSPEND is enabled, otherwise we
> > > > > > get a link error:
> > > > > > 
> > > > > > arch/arm/mach-vexpress/built-in.o: In function `tc2_pm_init':
> > > > > > arch/arm/mach-vexpress/tc2_pm.c:389: undefined reference to `mcpm_loopback'
> > > > > 
> > > > > Arnd,
> > > > > 
> > > > > We are having reports of TC2 not booting with MCPM enabled. Lorenzo
> > > > > was investigating this but then headed for Linaro Connect this week,
> > > > > so we don't have yet a resolution. Can this patch be postponed for
> > > > > a later -rc?
> > > > 
> > > > Why?
> > > > 
> > > > This patch isn't forcing MCPM to be enabled for Versatile Express.
> > > > 
> > > > * In order to build tc2_pm.c, MCPM must already be enabled (the
> > > >   feature depends on MCPM in the Kconfig already)
> > > > * When this feature is enabled, the above link error occurs if
> > > >   ARM_CPU_SUSPEND is not also enabled.
> > > > 
> > > > So, it is merely fixing the requirement that tc2_pm.c needs the CPU
> > > > suspend infrastructure, which in turn has no effect on whether MCPM
> > > > is enabled or not.
> > > 
> > > Because I think Lorenzo's plan was to disable MCPM for TC2. Which would
> > > make this patch moot.
> > 
> > I don't think that makes a difference - the two issues are orthogonal.
> > 
> > As the code stands today, it requires ARM_CPU_SUSPEND to be set, so
> > merging this change makes total sense.
> > 
> > If the code is temporarily disabled, then we still need this patch
> > merged to fix the error when the feature is re-enabled.  If the code
> > is changed later such that it doesn't need mcpm_loopback, then that's
> > the time to remove the select of this symbol.
> > 
> > If the code is removed, that is something which is not going to happen
> > during this merge window, so the patch still might as well be applied
> > to prevent build errors.
> 
> Russell,
> 
> I'm not arguing either way, I was just asking for a delay until Lorenzo
> (one other maintainer of the code that is in the Cc) has a chance to
> have his say, because I thought it was relevant (and I have explained why).
> 
> If Arnd feels he would rather push the patch now rather than (let say) late
> Monday, then I can give my Acked-by.

Sorry but I must disagree.

As the original author of that file _and_ actually being responsible for 
the bug fixed by that patch, I really don't understand why waiting for 
Lorenzo would be necessary here.


Nicolas
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