linux-kernel - Re: [PATCH] include/asm-generic/io.h: add 'UML' case just like 'no-MMU'

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Message-ID: <51CABFAC.1040505@nod.at>
Date:	Wed, 26 Jun 2013 12:17:16 +0200
From:	Richard Weinberger <richard@....at>
To:	Chen Gang <gang.chen@...anux.com>
CC:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Jeff Dike <jdike@...toit.com>, Arnd Bergmann <arnd@...db.de>,
	David Sharp <dhsharp@...gle.com>,
	"sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	uml-devel <user-mode-linux-devel@...ts.sourceforge.net>,
	uml-user <user-mode-linux-user@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] include/asm-generic/io.h: add 'UML' case just like 'no-MMU'

Am 26.06.2013 12:01, schrieb Chen Gang:
> On 06/26/2013 05:48 PM, Geert Uytterhoeven wrote:
>> On Wed, Jun 26, 2013 at 11:38 AM, Richard Weinberger <richard@....at> wrote:
>>>>>> Since the API itself already contents the meaning: "return NULL means
>>>>>> the arch has no related io memory",
>> No, NULL means it could not map the I/O memory.
>>
> 
> "it could not map the I/O memory" includes "has no related io memory".
> So it is enough for our case.
> 
>>>>>> Why not define a generic dummy one in "include/asm-generic/io.h" instead
>>>>>> of "HAS_IOMEM" (which has already spread many various places, and also,
>>>>>> most of new drivers have to know about it).
>>>>>>
>>>>>> e.g: in "include/asm-generic/io.h", if "CONFIG_HAS_IOMEM=n", define a
>>>>>> dummy ioremap() which return NULL ... (also need consider more details).
>>>>
>>>> Because we don't even want to build these drivers and not make them fail while
>>>> executing io memory related functions.
>> Indeed, it doesn't make sense to build drivers that cannot work.
>> And they may fail in a very bad way.
> 
> That is our 'platform' guys feeling, not the 'module' guys, as
> 'platform' guys, it is better to provide the choice to 'module' guys,
> and let them decide by themselves, not forced by us.

FYI, this is my last reply to this thread.

As Geert and I said, drivers which need io memory have to depend on HAS_IOMEM=y.
If an arch does not have io memory these drivers cannot work and therefore we don't
want them built.

Over and out,
//richard
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