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

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Message-ID: <51CAB556.4070700@asianux.com>
Date:	Wed, 26 Jun 2013 17:33:10 +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 05:03 PM, Richard Weinberger wrote:
> 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".
> 

Since the API itself already contents the meaning: "return NULL means
the arch has no related io memory",

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).


All together, I think: it is the duty of "asm-generic/io.h" to process
this issue, not the duty of many drivers and some architectures.


> 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.
> 

At least now, it seems it is the only suitable way to fix this issue.  :-(


> 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.

Excuse me, I did not look at the details of this driver. Maybe it just
like you said above.


Thanks.
-- 
Chen Gang

Asianux Corporation
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