linux-kernel - Re: Fwd: Re: sparc64: Build failure due to commit f1600e549b94 (sparc: Make sparc64 use scalable lib/iommu-common.c functions)

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Message-ID: <1429515520.12716.3.camel@ellerman.id.au>
Date:	Mon, 20 Apr 2015 17:38:40 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Sowmini Varadhan <sowmini.varadhan@...cle.com>,
	benh@...nel.crashing.org, aik@....ibm.com, anton@....ibm.com,
	paulus@...ba.org, linuxppc-dev@...ts.ozlabs.org,
	sparclinux@...r.kernel.org, davem@...emloft.net,
	linux-kernel@...r.kernel.org
Subject: Re: Fwd: Re: sparc64: Build failure due to commit f1600e549b94
 (sparc: Make sparc64 use scalable lib/iommu-common.c functions)

On Sun, 2015-04-19 at 22:17 -0700, Guenter Roeck wrote:
> Hi Michael,

Hi Guenter,

> On 04/19/2015 08:01 PM, Michael Ellerman wrote:
> 
> > Someone needs to be doing s390/alpha builds with that enabled anyway, because
> > otherwise a clash between generic code and s390/alpha won't be caught.
> >
> > Or if that's too hard we can rename the powerpc version, but it seems silly to
> > rename a powerpc variable to deal with a debug option that is only useful for
> > s390/alpha.
> 
> The debug option is intended for all _other_ architectures, to ensure that
> changes made for those don't break alpha/s390 builds. alpha/s390 have
> ARCH_NEEDS_WEAK_PER_CPU and don't need the debug option.

But that can't actually work. If you introduce a percpu variable in generic
code that has the same name as a variable in the s390/alpha code, the only way
you can detect that is by building for s390/alpha.

Sure it might catch two variables in generic code that have the same name, but
that will get caught as soon as someone does a s390/alpha build anyway - which
is at least every night for linux-next.

More likely it catches cases like this, which is variables in code that will
never build for s390/alpha. So it just seems like a PITA to me.

> Sowmini's patch would change the variable name in the lib/ code. But that was
> not the question here. The question was if the powerpc code could be changed
> to use the generic iommu code instead of using the powerpc specific code.

Not for this merge window sorry, we need to test it properly.

cheers



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