linux-kernel - Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses

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Date:	Mon, 20 Jun 2011 09:31:22 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Ryan Mallon <rmallon@...il.com>
Cc:	Petr Tesarik <ptesarik@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fenghua Yu <fenghua.yu@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Luck <tony.luck@...el.com>, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
	linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary
 physical addresses


* Ryan Mallon <rmallon@...il.com> wrote:

> On 17/06/11 19:30, Ingo Molnar wrote:
> >* Petr Tesarik<ptesarik@...e.cz>  wrote:
> >
> >>This patch series enhances /dev/mem, so that read and write is
> >>possible at any address. The patchset includes actual
> >>implementation for x86.
> >This series lacks a description of why this is desired.
> >
> >My strong opinion is that it's not desired at all: /dev/mem never
> >worked beyond 4G addresses so by today it has become largely obsolete
> >and is on the way out really.
> >
> >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.
> 
> There are drivers where this makes sense. For example an FPGA 
> device with a proprietary register layout on the memory bus can be 
> done this way. [...]

So you want us to help vendors screw users with insane, proprietary, 
user-space drivers with sekrit binary blobs?

Wow.

Thanks,

	Ingo
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