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

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Date:	Mon, 01 Jul 2013 09:40:25 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Chen Gang <gang.chen@...anux.com>
CC:	Richard Weinberger <richard@....at>,
	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>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] include/asm-generic/io.h: add 'UML' case just like 'no-MMU'

On 06/26/2013 06:22 PM, Chen Gang wrote:
> On 06/26/2013 06:17 PM, Richard Weinberger wrote:
>> 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.
> 

Hmm, if the modules select 'COMPILE_TEST', it is better to let asm-generic
support this features (at least, not forbid it)

So how about the diff below ?  ;-)

---------------------------diff begin-----------------------------------

diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index d5afe96..ede3775 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -303,13 +303,17 @@ static inline void *phys_to_virt(unsigned long address)
 /*
  * Change "struct page" to physical address.
  *
- * This implementation is for the no-MMU case only... if you have an MMU
- * you'll need to provide your own definitions.
+ * This for the no-MMU, or no-IOMEM but still try to COMPILE_TEST cases.
+ * if you have an MMU and IOMEM, you'll need to provide your own definitions.
  */
-#ifndef CONFIG_MMU
+#if !defined(CONFIG_MMU) || \
+	(!defined(CONFIG_HAS_IOMEM) && defined(COMPILE_TEST))
 static inline void __iomem *ioremap(phys_addr_t offset, unsigned long size)
 {
+#if !defined(CONFIG_MMU)
 	return (void __iomem*) (unsigned long)offset;
+#else
+	return NULL;
 }
 
 #define __ioremap(offset, size, flags)	ioremap(offset, size)
@@ -325,7 +329,7 @@ static inline void __iomem *ioremap(phys_addr_t offset, unsigned long size)
 static inline void iounmap(void __iomem *addr)
 {
 }
-#endif /* CONFIG_MMU */
+#endif /* !MMU || (!HAS_IOMEM && COMPILE_TEST) */
 
 #ifdef CONFIG_HAS_IOPORT
 #ifndef CONFIG_GENERIC_IOMAP

---------------------------diff end-------------------------------------

> It is really the time for stopping discussion, and thank you all for
> spending your time resources on this discussion.
> 
> Next, I will send related patch for it (also cc to you all).
> 
> 
> Thanks.
> 


-- 
Chen Gang
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