Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses
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- To: Ingo Molnar <mingo@xxxxxxx>
- Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses
- From: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>
- Date: Fri, 17 Jun 2011 10:41:25 +0100
- Cc: Petr Tesarik <ptesarik@xxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Fenghua Yu <fenghua.yu@xxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Paul Mundt <lethal@xxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Tony Luck <tony.luck@xxxxxxxxx>, x86@xxxxxxxxxx, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linux-sh@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Arjan van de Ven <arjan@xxxxxxxxxxxxx>, Dave Jones <davej@xxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
- In-reply-to: <20110617093032.GA19235@elte.hu>
- List-id: <linux-ia64.vger.kernel.org>
- References: <201106171038.25988.ptesarik@suse.cz> <20110617093032.GA19235@elte.hu>
- User-agent: Mutt/1.5.19 (2009-01-05)
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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