Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753317Ab0HWGbp (ORCPT ); Mon, 23 Aug 2010 02:31:45 -0400 Received: from cantor.suse.de ([195.135.220.2]:53208 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751978Ab0HWGbn (ORCPT ); Mon, 23 Aug 2010 02:31:43 -0400 Date: Mon, 23 Aug 2010 08:31:42 +0200 Message-ID: From: Takashi Iwai To: Zhenyu Wang Cc: Eric Anholt , David Airlie , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] agp/intel: Fix dma mask for Sandybridge In-Reply-To: <20100823061922.GD29442@zhen-devel.sh.intel.com> References: <20100823013507.GA29442@zhen-devel.sh.intel.com> <20100823054303.GC29442@zhen-devel.sh.intel.com> <20100823061922.GD29442@zhen-devel.sh.intel.com> User-Agent: Wanderlust/2.15.6 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.7 Emacs/23.1 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1184 Lines: 37 At Mon, 23 Aug 2010 14:19:22 +0800, Zhenyu Wang wrote: > > On 2010.08.23 08:02:42 +0200, Takashi Iwai wrote: > > > > Also, I don't understand the logic of 40bit addr calculation: > > > > > static unsigned long intel_gen6_mask_memory(struct agp_bridge_data *bridge, > > > dma_addr_t addr, int type) > > > { > > > /* Shift high bits down */ > > > addr |= (addr >> 28) & 0xff; > > > > Isn't it 0xff0? > > > > No. This depends on hw 32bit PTE format for sandybridge. > > bit 31 bit 11 bit 4 bit 0 > |<-physical addr 31:12->|<-physical addr 39:32->|<-cache ctl 3:1->|valid| Then I really don't understand why it works. You shift 28bit and mask with 0xff. Obviously it overwrite bits 0:3 with original 28:31 bits. Masking 0xff0 fixes the issue. And, the information like above would be greatly helpful if put into either changelog or comment... thanks, Takashi -- 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/