From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753557AbeE3O44 (ORCPT ); Wed, 30 May 2018 10:56:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:33986 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751289AbeE3O4w (ORCPT ); Wed, 30 May 2018 10:56:52 -0400 Date: Wed, 30 May 2018 09:56:50 -0500 From: Bjorn Helgaas To: okaya@codeaurora.org Cc: Christoph Hellwig , Gabriele Paoloni , "open list:DOCUMENTATION" , linux-pci@vger.kernel.org, Keith Busch , Kai-Heng Feng , Ingo Molnar , Christoffer Dall , Jonathan Corbet , timur@codeaurora.org, "Rafael J. Wysocki" , Dongdong Liu , David Rientjes , Thymo van Beers , "Paul E. McKenney" , Frederick Lawler , Konrad Rzeszutek Wilk , Marc Zyngier , linux-arm-msm@vger.kernel.org, Frederic Weisbecker , Bjorn Helgaas , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Oza Pawandeep , Greg Kroah-Hartman , open list Subject: Re: [PATCH] PCI: Add pci=safemode option Message-ID: <20180530145650.GA39853@bhelgaas-glaptop.roam.corp.google.com> References: <1527650389-31575-1-git-send-email-okaya@codeaurora.org> <20180530043103.GA19734@kroah.com> <6c317ed8-cca3-8862-5f3b-12cf14e4d53b@codeaurora.org> <20180530073735.GA28793@infradead.org> <6dfe2db8f974d94c9867f30ec83d9333@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6dfe2db8f974d94c9867f30ec83d9333@codeaurora.org> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 30, 2018 at 12:44:29AM -0700, okaya@codeaurora.org wrote: > On 2018-05-30 00:37, Christoph Hellwig wrote: > > On Tue, May 29, 2018 at 09:41:33PM -0700, Sinan Kaya wrote: > > > Bjorn and I discussed the need for such a "safe" mode feature when you > > > want to bring up PCI for a platform. You want to turn off everything > > > as > > > a starter and just stick to bare minimum. > > > > Can we please make it a config option the instead of adding code > > to every kernel? Also maybe the bringup should be in the name > > to make this more clear? > > One other requirement was to have a runtime option rather than compile time > option. > > When someone reported a problem, we wanted to be able to say "use this > option and see if system boots" without doing any bisects or recompilation. > > This would be the first step in troubleshooting a system to see if > fundamental features are working. > > I don't mind changing the name > Bjorn mentioned safe option. I made it safemode. I am looking at Bjorn for > suggestions at this moment. This *was* my idea, but I'm starting to think it was a bad idea. I don't want people to use pci= parameters as the normal way to get a system to boot. That would be a huge support hassle (putting things in release notes, diagnosing problems when people forget it, etc). But the parameters *are* useful for debugging. If we had a "pci=safemode" and it avoided some problem, the next step would be to narrow it down by using the more specific flags (pci=nomsi, pci=noari, pci=no_ext_tags, etc). So I think 95% of the value is in the specific flags, and a "pci=safemode" might add a little bit of value but at the cost of a small but nagging maintenance concern and code clutter. Bjorn