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

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Message-ID: <7990730.tNeXHUrIig@wuerfel>
Date:	Thu, 17 Dec 2015 20:57:04 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Wolfram Sang <wsa@...-dreams.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 Thursday 17 December 2015 20:40:17 Wolfram Sang wrote:
> > > 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.
> > 
> > I generally like __maybe_unused, but it's a matter of personal preference.
> > We could avoid the __maybe_unused if the reg_slave/unreg_slave callback
> > pointers are always available in struct i2c_algorithm.
> 
> Yes, I was thinking in this direction, looking at how PM does it. Needs
> some playing around, though.

I think PM gets it slightly wrong, the way you have to use #ifdef leads
to subtle bugs all the time, and I actually have a patch that converts
a few dozen drivers to use __maybe_unused to shut up build warnings and
errors.

What you can do though is to use a reference like

#define __i2c_slave_ptr(x) (IS_ENABLED(CONFIG_I2C_SLAVE) ? (x) : NULL)

	...
	.reg_slave = __i2c_slave_ptr(em_i2c_reg_slave),
	.unreg_slave = __i2c_slave_ptr(em_i2c_unreg_slave),
	...

This has the same effect as the __maybe_unused annotation.

	Arnd
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