From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lanttor Subject: why the PAGE_OFFSET is not 0xc0000000 on m68k platform Date: Thu, 21 May 2009 12:17:41 +0800 Message-ID: <4A14D5E5.9070103@freescale.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from az33egw02.freescale.net ([192.88.158.103]:59523 "EHLO az33egw02.freescale.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750757AbZEUEIQ (ORCPT ); Thu, 21 May 2009 00:08:16 -0400 Received: from az33smr02.freescale.net (az33smr02.freescale.net [10.64.34.200]) by az33egw02.freescale.net (8.14.3/az33egw02) with ESMTP id n4L48HeJ029885 for ; Wed, 20 May 2009 21:08:17 -0700 (MST) Received: from zch01exm25.fsl.freescale.net (zch01exm25.ap.freescale.net [10.192.129.217]) by az33smr02.freescale.net (8.13.1/8.13.0) with ESMTP id n4L48FSu027530 for ; Wed, 20 May 2009 23:08:16 -0500 (CDT) Sender: linux-m68k-owner@vger.kernel.org List-Id: linux-m68k@vger.kernel.org To: linux-m68k@vger.kernel.org Hi, I see the definition of PAGE_OFFSET on m68k platform like that: #define PAGE_OFFSET (PAGE_OFFSET_RAW) #ifdef CONFIG_MMU #ifndef CONFIG_SUN3 #define PAGE_OFFSET_RAW 0x00000000 #else #define PAGE_OFFSET_RAW 0x0E000000 #endif #else #define PAGE_OFFSET_RAW CONFIG_RAMBASE #endif In my understanding, the kernel page mapping depends on PAGE_OFFSET. For example, if PAGE_OFFSET is 0x00000000 (assuming 256M memory), the kernel virtual address will be at (0x00000000 - 0x10000000), right? Could this incur some side effect? I see the definition of PAGE_OFFSET is 0xc0000000 on much platforms. Thanks, -- Best Regards, Lanttor