Re: [PATCH 00/10] Enhance /dev/mem to allow read/write ofarbitrary physical addresses

From: Russell King - ARM Linux
Date: Fri Jun 17 2011 - 05:46:25 EST

On Fri, Jun 17, 2011 at 11:30:32AM +0200, Ingo Molnar wrote:
> I'm aware of these current /dev/mem uses:
> - Xorg maps below 4G non-RAM addresses and the video BIOS
> - It used to have some debugging role but these days kexec and kgdb
> has largely taken over that role - partly due to the 4G limit.
> - there's some really horrible out-of-tree drivers that do mmap()s
> via /dev/mem, those should be fixed if they want to move beyond
> 4G: their char device should be mmap()able.
> - all distro kernel's i'm aware of use CONFIG_STRICT_DEVMEM=y, which
> restricts /dev/mem to non-RAM pages of physical memory.
> [ With the sad inclusion of the first 1MB, which Xorg needs. ]

There's another use case for /dev/mem:

- debugging via devmem2 on embedded platforms, where you want to be able
to boot a kernel, and then peek and poke at MMIO registers either to
verify register values or test things out.
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