From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2992675AbXDDGEe (ORCPT ); Wed, 4 Apr 2007 02:04:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S2992677AbXDDGEe (ORCPT ); Wed, 4 Apr 2007 02:04:34 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:34412 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2992675AbXDDGEd (ORCPT ); Wed, 4 Apr 2007 02:04:33 -0400 Subject: Re: [PATCH] Stop pmac_zilog from abusing 8250's device numbers. From: David Woodhouse To: Paul Mackerras Cc: Alan Cox , Brad Boyer , linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org In-Reply-To: <17939.15726.114059.679277@cargo.ozlabs.ibm.com> References: <1175610345.2665.15.camel@shinybook.infradead.org> <17938.57292.870224.132415@cargo.ozlabs.ibm.com> <1175642916.10567.24.camel@shinybook.infradead.org> <20070403212928.GA12951@cynthia.pants.nu> <20070404022544.59b022a6@the-village.bc.nu> <17939.10130.687893.167511@cargo.ozlabs.ibm.com> <1175663999.2932.8.camel@shinybook.infradead.org> <17939.15726.114059.679277@cargo.ozlabs.ibm.com> Content-Type: text/plain Date: Wed, 04 Apr 2007 02:03:54 -0400 Message-Id: <1175666635.2932.17.camel@shinybook.infradead.org> Mime-Version: 1.0 X-Mailer: Evolution 2.10.0 (2.10.0-7.fc7.dwmw2.2) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2007-04-04 at 15:53 +1000, Paul Mackerras wrote: > David Woodhouse writes: > > > Why? What's so special about the name 'ttyS'? > > It's the name that users of Linux expect built-in serial ports to have. Not really. The norm under Linux is for non-8250 ports to use properly-registered device numbers and names. There's not many which are still broken in this respect -- it's basically pmac_zilog and some Sun UARTs, isn't it? And even if it _were_ true, it wouldn't be a particularly good reason for changing the way we handle serial ports under Linux. > > > The built-in ports can generally be enumerated early on boot in a > > > stable order, and they should be assigned the low ttySn numbers, > > > regardless of what chip is used to implement them. > > > > I don't see why that 'should' be the case. Certainly it _isn't_ the case > > on most supported platforms -- we have separate device numbers, and > > names, for most types of ports. There's only one or two drivers which > > abuse ttySn for anything other than 8250 ports. > > It 'should' be the case because that is what is easiest for users and > makes most sense from a user's point of view. I really don't buy that argument. People cope perfectly well with /dev/ttySA0 on StrongARM, with /dev/ttySC0 on SH, etc. If it isn't an 8250, it doesn't usually get called ttyS0. There's certainly nothing _easier_ about ttyS0. Unless it's really an effort to type that extra character :) > You still haven't given any reason why a user should have to know or > care whether the built-in serial ports on his/her computer are > implemented with a 16C550 chip or a Z85C30 chip or something else. Because that's the way serial ports are named under Linux. If you want to change that, then take it up with the serial maintainer -- but pmac_zilog as it is upstream at the moment is just _broken_. The module just doesn't load if you have 8250 built in or loaded. That's what you get when you abuse device numbers belonging to another driver. > In any case your patch is a user-visible incompatible API change and > will break existing working setups, so it should only be put in after > suitable warning has been given. Maybe we need a module parameter to > select between the old and new behaviour to ease the transition. Perhaps that's true; I'd certainly never seen a working setup with pmac_zilog, because I'd never actually seen the module load. It's always failed for me, because I have 8250 support built in to my kernels. -- dwmw2