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 11:03:56 +0200
From:	Richard Weinberger <richard@....at>
To:	Chen Gang <gang.chen@...anux.com>
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'

Am 26.06.2013 10:58, schrieb Chen Gang:
> 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.

No.
Not setting CONFIG_HAS_IOMEM=y means "This arch has no io memory and therefore no
functions to mess with it".

Let's get back to the real problem,
drivers/ptp/ptp_pch.c does not build on UML (and I'm very sure also not on S390).
Fix the issue by making it depend on HAS_IOMEM.

Btw: Did you actually look at this driver? There is *zero* reason to have it on UML.
...like 99.9% of all other drivers which use io memory.

Thanks,
//richard
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