Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759284Ab2FFXST (ORCPT ); Wed, 6 Jun 2012 19:18:19 -0400 Received: from mail-vc0-f174.google.com ([209.85.220.174]:63046 "EHLO mail-vc0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757317Ab2FFXSR convert rfc822-to-8bit (ORCPT ); Wed, 6 Jun 2012 19:18:17 -0400 MIME-Version: 1.0 In-Reply-To: <1339023839.25761.764.camel@lyra> References: <20120427190033.GA17588@ldl.usa.hp.com> <20120606135009.GB1517@srcf.ucam.org> <1338999463.25761.630.camel@lyra> <20120606162703.GA6779@srcf.ucam.org> <1339003956.25761.667.camel@lyra> <20120606174202.GA8750@srcf.ucam.org> <1339006060.25761.689.camel@lyra> <1339023839.25761.764.camel@lyra> Date: Wed, 6 Jun 2012 17:18:16 -0600 Message-ID: Subject: Re: [PATCH] Disable Bus Master on PCI device shutdown From: Myron Stowe To: Khalid Aziz Cc: Matthew Garrett , linux-kernel@vger.kernel.org, bhelgaas@google.com, linux-pci@vger.kernel.org, "Eric W. Biederman" Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2402 Lines: 58 On Wed, Jun 6, 2012 at 5:03 PM, Khalid Aziz wrote: > On Wed, 2012-06-06 at 14:16 -0600, Myron Stowe wrote: >> Hay Khalid, >> >> I've been following this discussion but still do not understand what the >> perceived correct fix is for the situation you were originally trying to >> circumvent - namely, stopping NIC devices from triggering DMA activity >> upon receipt of an incoming packet. >> >> From the discussion it sounds like a driver, upon shutdown, can end >> all active I/O >> clearing the I/O queue, and also (?) shut down its DMA engine, and may >> also go as far as disabling the Bus Master bit. >> >> What was occurring in the original issue - was the driver in question not >> shutting down its DMA engine for some, possibly valid, reason? >> >> Thanks, >> ?Myron > > Hi Myron, > > The last driver issue with kexec was reported on kexec mailing list in > July of last year and that was with qla driver. From what H Peter Anvin > described, the driver left DMA engine running. > > For the issue I found on an ia64 platform, it was so many years ago that > you are now taxing my old and decrepit memory :) Yeah, if it was more than a couple of weeks ago then I'm likely to have forgotten myself. If you can find it great but don't spend too much time digging. I just wanted some validation of my understanding - o That drivers must consider both "active I/O" and "DMA" (when shutting down), o That the Bus Master disablement was trying to compensate for a driver not quiescing "DMA" as it probably should have (I wasn't sure if these were separate capabilities and/or if there was possibly a valid reason for a driver leaving "DMA" in an enabled state upon shutdown - i.e. Wake on LAN or something similar). Myron > I am digging through > old internal bug reports and will let you know once I find that original > bug report. > > ==================================================================== > Khalid Aziz ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Unix Systems Lab > (970)898-9214 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?Hewlett-Packard > khalid.aziz@hp.com ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?Fort Collins, CO > -- 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/