Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751781AbZIHRvu (ORCPT ); Tue, 8 Sep 2009 13:51:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751954AbZIHRvu (ORCPT ); Tue, 8 Sep 2009 13:51:50 -0400 Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:53508 "EHLO www.etchedpixels.co.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751750AbZIHRvt (ORCPT ); Tue, 8 Sep 2009 13:51:49 -0400 Date: Tue, 8 Sep 2009 18:53:06 +0100 From: Alan Cox To: Alan Stern Cc: linux-ide@vger.kernel.org, Kernel development list Subject: Re: Limiting DMA speeds for individual IDE drives Message-ID: <20090908185306.0f30c07b@lxorguk.ukuu.org.uk> In-Reply-To: References: X-Mailer: Claws Mail 3.7.2 (GTK+ 2.14.7; x86_64-redhat-linux-gnu) 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 Content-Length: 1428 Lines: 29 > I've got a situation where a drive claims to be capable of supporting > UDMA/100, but it's in a noisy environment and gets lots of errors at > that speed. I'd like to limit it to UDMA/66 or even UDMA/33. That should never occur with a proper cable and I would be concerned the fault might be something more problematic such as speed misconfiguration or an incompatibility. Which driver is in use ? > The hdparm command should be able to do this but I can't run it until > the system has booted, by which time a bunch of CRC and possibly other > errors have already occurred. Ideally it should be possible to limit Only the data transfers are CRC protected and at high speed, but noise at low speed would be a real concern as the commands are sent low speed but without protection on PATA devices - so a bit flip can send a DMA to the wrong sector. > the speed starting as early as device detection, but I can't find any > way to do it. Is there support for such a thing or will I have to hack > it in? You can disallow DMA but not clip DMA to UDMA33 with the old driver. You could disallow DMA at boot and reallow it with a speed set by hdparm in your boot scripts... -- 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/