linux-kernel - Re: Device driver memory 'mmap()' function helper cleanup

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Message-ID: <516E88A9.9070200@ti.com>
Date:	Wed, 17 Apr 2013 14:34:01 +0300
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Clemens Ladisch <clemens@...isch.de>,
	Arnd Bergmann <arnd@...db.de>, Takashi Iwai <tiwai@...e.de>,
	Mauro Carvalho Chehab <mchehab@...hat.com>
Subject: Re: Device driver memory 'mmap()' function helper cleanup

On 2013-04-17 06:12, Linus Torvalds wrote:
> Guys, I just pushed out a new helper function intended for cleaning up
> various device driver mmap functions, because they are rather messy,
> and at least part of the problem was the bad impedance between what a
> driver author would want to have, and the VM interfaces to map a
> memory range into user space with mmap.
> 
> Some drivers would end up doing extensive checks on the length of the
> mappings and the page offset within the mapping, while other drivers
> would end up doing no checks at all.
> 
> The new helper is in commit b4cbb197c7e7 ("vm: add vm_iomap_memory()
> helper function"), but I didn't actually commit any *users* of it,
> because I just have this untested patch-collection for a few random
> drivers (picked across a few different driver subsystems, just to make
> it interesting).  I did that largely just to check the different use
> cases, but I don't actually tend to *use* all that many fancy drivers,
> so I don't have much of a way of testing it.

Should there be a similar helper that uses remap_pfn_range() instead of
io_remap_pfn_range()?

Some fb drivers use remap_pfn_range(), and I'm not sure if there could
be some side effects on some platforms if they are changed to use
io_remap_pfn_range(). At least mips and sparc seem to have their own
versions for io_remap_pfn_range().

 Tomi



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