Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755132Ab1FSXC2 (ORCPT ); Sun, 19 Jun 2011 19:02:28 -0400 Received: from mail-iy0-f174.google.com ([209.85.210.174]:56637 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755093Ab1FSXC0 (ORCPT ); Sun, 19 Jun 2011 19:02:26 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:content-type:content-transfer-encoding; b=Mx2jx99mUs73B3XWM/coFXUkbk93MYOqWJPbx0eWBgdo9EA73/wm/kVvgS4vBR9Kfr rySn0RZOY1dfCJgv74cP0gQCmO1fvxC37Seaba4ups/Zi9T6S05PnXHPApgxBymBa7Ci cuxGeZxT0Fb4875rmaZkb7uikKt5+iFCE3onU= Message-ID: <4DFE7FF9.9070406@gmail.com> Date: Mon, 20 Jun 2011 09:02:17 +1000 From: Ryan Mallon User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110424 Lightning/1.0b2 Thunderbird/3.1.10 MIME-Version: 1.0 To: Ingo Molnar CC: Petr Tesarik , Andrew Morton , Fenghua Yu , "H. Peter Anvin" , Ingo Molnar , Paul Mundt , Russell King , Thomas Gleixner , Tony Luck , x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org, Arjan van de Ven , Dave Jones , Linus Torvalds Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses References: <201106171038.25988.ptesarik@suse.cz> <20110617093032.GA19235@elte.hu> In-Reply-To: <20110617093032.GA19235@elte.hu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1554 Lines: 37 On 17/06/11 19:30, Ingo Molnar wrote: > * Petr Tesarik 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. The FPGA can simply be mapped in user-space via /dev/mem and handled there. If the device requires no access other than memory bus reads and writes then writing a custom char device driver just to get an mmap function seems a bit overkill. ~Ryan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/