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

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Date:	Wed, 26 Jun 2013 16:58:05 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Richard Weinberger <richard@....at>
CC:	Jeff Dike <jdike@...toit.com>, Arnd Bergmann <arnd@...db.de>,
	dhsharp@...gle.com,
	Mark Brown <broonie@...nsource.wolfsonmicro.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>
Subject: Re: [PATCH] include/asm-generic/io.h: add 'UML' case just like 'no-MMU'

On 06/26/2013 04:39 PM, Richard Weinberger wrote:
>>>>> >>>> The drivers internal code has already check the related return value,
>>>>> >>>> so it is the architecture's duty to 'tell' the driver whether support
>>>>> >>>> io memory (e.g. define ioremap, but return NULL).
>>> >> It does so already by setting CONFIG_HAS_IOMEM=n
>> > 
>> > Excuse me, I use "grep -rn ioremap *" under "include/" and "arch/um/"
>> > directory, but can not find the related definition for 'ioremap'.
>> > 
>> > Is there another declaration or definition way which I don't know ?
>> > (maybe it is).
> Both UML and s390 (in the !CONFIG_PCI) do not define ioremap() because
> without io memory you cannot have a ioremap().
> 

I assume if ioremap() return NULL, it means "without io memory", is it
correct ?

If it is correct, "define a dummy ioremap(), and return NULL" is just
the meaning that you mentioned above.

If so, for UML, it is not requirement, but recommend to define a dummy
ioremap() which return NULL, so can be generic enough to mach all cases.


>> > For our case, the ".config" file does not define 'CONFIG_HAS_IOMEM', can
>> > I assume it means "CONFIG_HAS_IOMEM=n" ?
> If I'm not mistaken it works the other way around.
> All archs except UML and s390 set CONFIG_HAS_IOMEM=y.

I guess so, too.


Thanks.
-- 
Chen Gang

Asianux Corporation
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