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

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Date:	Thu, 29 May 2014 11:26:44 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"H. Peter Anvin" <hpa@...or.com>
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 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.

	Arnd
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