From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from az33egw01.freescale.net (az33egw01.freescale.net [192.88.158.102]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "az33egw01.freescale.net", Issuer "Thawte Premium Server CA" (verified OK)) by ozlabs.org (Postfix) with ESMTP id DDBE2DDE01 for ; Thu, 6 Dec 2007 04:46:16 +1100 (EST) Message-ID: <4756E3E8.8090102@freescale.com> Date: Wed, 05 Dec 2007 11:46:16 -0600 From: Scott Wood MIME-Version: 1.0 To: michael.firth@bt.com Subject: Re: Maximum ioremap size for ppc arch? References: <36D7B34A3A79F84F82FA0C154F299F2506080F6F@E03MVX1-UKDY.domain1.systemhost.net> In-Reply-To: <36D7B34A3A79F84F82FA0C154F299F2506080F6F@E03MVX1-UKDY.domain1.systemhost.net> Content-Type: text/plain; charset=UTF-8; format=flowed Cc: linuxppc-embedded@ozlabs.org List-Id: Linux on Embedded PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , michael.firth@bt.com wrote: > My main queries are: 1) Why did changing the kernel base address to > 0x80000000 make the system unstable? Because there's a bug somewhere. :-) > 2) Currently IMMRBAR has the same physical and virtual address. Does > this need to be the case? No, and it is not done that way in arch/powerpc. > 3) Why the kernel is designed to run at 0xc0000000? My guess is because it's a number that Linus pulled out of thin air back when a gig of RAM was unimaginably large. :-P > This seems to leave only 1GB of addressing space for all the > physically addressable memory (RAM + ioremapped + registers), while > reserving 3GB of space for user processes. The 3GB is presumably > mostly unusable on a system without a large amount of swap, as the > 1GB limit on memory will prevent much more than that being available > for user space. Well, it's also useful for sparse mappings, but I agree that the 3/1 split is probably suboptimal for most workloads. -Scott