linux-kernel - Re: [PATCH v2] um: add dummy ioremap and iounmap functions

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Date:   Wed, 21 Jun 2017 23:30:52 +0200
From:   Richard Weinberger <richard@....at>
To:     Logan Gunthorpe <logang@...tatee.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        uml-devel <user-mode-linux-devel@...ts.sourceforge.net>,
        Stephen Bates <sbates@...thlin.com>,
        Jeff Dike <jdike@...toit.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2] um: add dummy ioremap and iounmap functions

Logan,

Am 21.06.2017 um 23:25 schrieb Logan Gunthorpe:
> Poke.
> 
> On 08/06/17 01:17 PM, Richard Weinberger wrote:
>> Am 08.06.2017 um 20:53 schrieb Logan Gunthorpe:
>> IMHO an ifdef in scatterlist code does not hurt.
>> It is equally ugly than mocking ioremap for UML.
> 
> I disagree. Having ifdefs scattered around all call sites of a function
> is *much* worse than having an extra mock function tucked away in a
> header file somewhere.
> 
> It's a very common pattern in the kernel for providers of functions that
> depend on a configuration option to provide mock functions when the
> configuration option is not selected. This prevents needing every caller
> of said function to put #ifdefs around the call. For a few examples:
> 
> include/linux/blkdev.h:1952
> include/linux/dax.h:24
> include/linux/pci.h:1329
> 
> And, frankly, it's _exactly_ what Linus Torvalds himself was arguing
> against in the link I sent up-thread [1].
> 
>> So, I'm puzzled.
>> Arnd, what do you think?
>> Shall !HAS_IOMEM archs just mock these functions?
> 
> So, once again, 'um' is now the only architecture that has this problem
> since tile and s390 accepted my patches (and without a fuss too). So can
> you please consider merging this patch or proposing something that will
> also fix the problem?

Since Arnd stays silent and um is the only remaining odd-ball, let's merge this
in v4.13.

Thanks,
//richard