Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261563AbVETUAO (ORCPT ); Fri, 20 May 2005 16:00:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261562AbVETUAO (ORCPT ); Fri, 20 May 2005 16:00:14 -0400 Received: from alog0356.analogic.com ([208.224.222.132]:447 "EHLO chaos.analogic.com") by vger.kernel.org with ESMTP id S261564AbVETUAG (ORCPT ); Fri, 20 May 2005 16:00:06 -0400 Date: Fri, 20 May 2005 15:59:44 -0400 (EDT) From: "Richard B. Johnson" Reply-To: linux-os@analogic.com To: Valdis.Kletnieks@vt.edu cc: Geert Uytterhoeven , Jan-Benedict Glaw , Linux kernel Subject: Re: Screen regen buffer at 0x00b8000 In-Reply-To: <200505201945.j4KJjSAW014218@turing-police.cc.vt.edu> Message-ID: References: <20050520141434.GZ2417@lug-owl.de> <200505201945.j4KJjSAW014218@turing-police.cc.vt.edu> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1678 Lines: 39 On Fri, 20 May 2005 Valdis.Kletnieks@vt.edu wrote: > On Fri, 20 May 2005 21:26:59 +0200, Geert Uytterhoeven said: >> On Fri, 20 May 2005, Richard B. Johnson wrote: > >>> I think that I've discovered a bug. I know that what I have written gets >>> to the screen buffer because I can read in back! This doesn't make >>> any sense. >> >> Even if it's only in the CPU cache, of course you can read it back (using the >> CPU, not DMA ;-). > > No, the bug is in Richard's assuming that because he can read it back in means > that it's in the screen buffer. In fact, it only means he wrote it into some > memory location that he can read back in. ;) > > Now if he added a description that verified that a read *from the screen > buffer* > (rather than "from where he wrote") shows his changes, *then* he'd have > something... > Well MAP_FIXED must either mmap the physical location I provided or it must fail. Since it didn't fail, I figure that it did what I told it to do. Now, that "FIXED" refers to a fixed offset. Geert is correct when he says that it's probably just in cache. Now begs the question... Why would a hardware buffer ever be cached? That's why I think I found a bug. It certainly shouldn't be cached. Cheers, Dick Johnson Penguin : Linux version 2.6.11.9 on an i686 machine (5554.17 BogoMips). Notice : All mail here is now cached for review by Dictator Bush. 98.36% of all statistics are fiction. - 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/