linux-kernel - Re: [PATCH] drivers/char/mem.c: Add /dev/ioports, supporting 16-bit and 32-bit ports

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Message-ID: <5387385B.1030203@zytor.com>
Date:	Thu, 29 May 2014 06:38:35 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	josh@...htriplett.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH] drivers/char/mem.c: Add /dev/ioports, supporting 16-bit
 and 32-bit ports

On 05/29/2014 02:26 AM, Arnd Bergmann wrote:
> On Wednesday 28 May 2014 14:41:52 H. Peter Anvin wrote:
>> On 05/19/2014 05:36 AM, Arnd Bergmann wrote:
>>>
>>> My feeling is that all devices we can think of fall into at least one
>>> of these categories:
>>>
>>> * legacy PC stuff that needs only byte access
>>> * PCI devices that can be accessed through sysfs
>>> * devices on x86 that can be accessed using iopl
>>>
>>
>> I don't believe PCI I/O space devices can be accessed through sysfs, but
>> perhaps I'm wrong?  (mmapping I/O space is not portable.)
> 
> The interface is there, both a read/write and mmap on the resource
> bin_attribute. But it seems you're right, neither of them is implemented
> on all architectures.
> 
> Only powerpc, microblaze, alpha, sparc and xtensa allow users to mmap
> I/O space, even though a lot of others could. The read-write interface
> is only defined for alpha, ia64, microblaze and powerpc.
> 

And how is that read/write interface defined?  Does it have the same
silly handling of data sizes?

	-hpa


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