From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753486AbYCPUq6 (ORCPT ); Sun, 16 Mar 2008 16:46:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752440AbYCPUqs (ORCPT ); Sun, 16 Mar 2008 16:46:48 -0400 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:41176 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1752534AbYCPUqs (ORCPT ); Sun, 16 Mar 2008 16:46:48 -0400 Date: Sun, 16 Mar 2008 20:31:09 +0000 From: Alan Cox To: Linus Torvalds Cc: Bartlomiej Zolnierkiewicz , Anders Eriksson , "Rafael J. Wysocki" , Jens Axboe , Ingo Molnar , Linux Kernel Mailing List Subject: Re: Linux 2.6.25-rc4 Message-ID: <20080316203109.50e8c526@core> In-Reply-To: References: <20080316140118.891732DC044@tippex.mynet.homeunix.org> <200803161907.04581.bzolnier@gmail.com> <20080316185602.79064f7c@core> X-Mailer: Claws Mail 3.3.1 (GTK+ 2.12.5; x86_64-redhat-linux-gnu) Organization: Red Hat UK Cyf., Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE, Y Deyrnas Gyfunol. Cofrestrwyd yng Nghymru a Lloegr o'r rhif cofrestru 3798903 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 16 Mar 2008 12:39:43 -0700 (PDT) Linus Torvalds wrote: > > > On Sun, 16 Mar 2008, Alan Cox wrote: > > > > No it doesn't. DRQ simply means "drive has more data for the controller > > if you want it". Interrupts are controlled via IEN and the interrupt line. > > A _lot_ of chips require you to clear the DRQ by taking the data they > have. Almost none and mostly very old ones. I'm not saying we shouldn't do it (except where it hangs the hardware - hence the FIFO flag) but for the traces presented and hardware reported it appears to be a bit of a red herring. > > If the drive wants to give us data and we end the transaction that is > > fine. In practice a tiny few devices crap themselves if we don't. > > More than a few tiny devices from what I remember. It tends to be the > other way around - most devices do *not* want to get new commands until > you've finished the previous one by draining the queues. Not in my experience having maintained a lot of ATA drivers for a very long time. In fact the changes for draining the DRQ went into libata only very recently because it was only when we had a distro sized userbase with PATA devices that it became apparent that a few corner case problems remained. Alan