linux-kernel - Re: [PATCH] i2c: allow building emev2 without slave mode again

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Message-ID: <20151217120157.GC3958@katana>
Date:	Thu, 17 Dec 2015 13:01:57 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	kbuild test robot <lkp@...el.com>, kbuild-all@...org,
	linux-i2c@...r.kernel.org,
	Niklas Söderlund 
	<niklas.soderlund+renesas@...natech.se>, linux-sh@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: allow building emev2 without slave mode again

On Mon, Dec 14, 2015 at 11:27:22PM +0100, Arnd Bergmann wrote:
> On Monday 14 December 2015 14:52:06 Wolfram Sang wrote:
> > > > What about not ifdeffing the inline function and keep the build error
> > > > whenever someone uses it without I2C_SLAVE being selected?
> > > 
> > > The inline function is only added there for the case that I2C_SLAVE is
> > > disabled, so that would be pointless.
> > > 
> > > However, what we could do is move the extern declaration outside of
> > > the #ifdef to make it always visible. The if(IS_ENABLED(CONFIG_I2C_SLAVE))
> > > check should then ensure that it never actually gets called, and we
> > > get a link error if some driver gets it wrong.
> > 
> > Yes, that's what I meant: move the whole function (as it was before your
> > patch) out of the CONFIG_I2C_SLAVE block. We should get a compiler error
> > even, because for !I2C_SLAVE, the client struct will not have the
> > slave_cb member.
> > 
> 
> But we don't want a compile-error for randconfig builds, and we don't
> want unnecessary #ifdef in the driver. 

My conclusion for now is:

There needs something to be done surely, but currently I don't have the
bandwidth to do it or even play around with it. I am not fully happy
with your patches as well because __maybe_unused has some kind of "last
resort" feeling to me.

So, to get the build failures away immediately I'd simply submit a patch
for the emev driver to select I2C_SLAVE and postpone the proper fix to
later.

That being said, thanks a lot for your input. I will surely come back to it.

All the best,

   Wolfram


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