From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756622AbbAFVsA (ORCPT ); Tue, 6 Jan 2015 16:48:00 -0500 Received: from mail-qa0-f47.google.com ([209.85.216.47]:50937 "EHLO mail-qa0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750921AbbAFVr6 (ORCPT ); Tue, 6 Jan 2015 16:47:58 -0500 Message-ID: <54AC580B.2050809@hurleysoftware.com> Date: Tue, 06 Jan 2015 16:47:55 -0500 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Arnd Bergmann CC: Greg Kroah-Hartman , One Thousand Gnomes , Jiri Slaby , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Sebastian Andrzej Siewior , Tony Lindgren , Grant Likely Subject: Re: [PATCH] serial: 8250: Make ISA ports optional References: <1420513785-23660-1-git-send-email-peter@hurleysoftware.com> <9492211.AECobr3jIN@wuerfel> <54ABF1E2.1010905@hurleysoftware.com> <6786513.g26uGMFKLE@wuerfel> In-Reply-To: <6786513.g26uGMFKLE@wuerfel> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/06/2015 02:43 PM, Arnd Bergmann wrote: > On Tuesday 06 January 2015 09:32:02 Peter Hurley wrote: >> On 01/06/2015 08:13 AM, Arnd Bergmann wrote: >>> On Monday 05 January 2015 22:09:45 Peter Hurley wrote: >>>> Some arches have no need to create unprobed 8250 ports; these phantom >>>> ports are primarily required for ISA ports which have no probe >>>> mechanism or to provide non-operational ports for userspace to >>>> configure (via TIOCSSERIAL and TIOCSERCONFIG ioctls). >>>> >>>> Provide CONFIG_SERIAL_8250_PHANTOM_UARTS knob to disable phantom port >>>> registration; ie., CONFIG_SERIAL_8250_PHANTOM_UARTS=N only registers >>>> probed ports (ACPI/PNP, "serial8250" platform devices, PCI, etc). >>>> >>>> Cc: Sebastian Andrzej Siewior >>>> Cc: Tony Lindgren >>>> Cc: Grant Likely >>>> Cc: Arnd Bergmann >>>> Signed-off-by: Peter Hurley >>> >>> The intent is definitely right, but I think a better approach is >>> possible. >>> >>> I haven't tried it here, but how about moving the serial8250_init >>> function into a separate module, along with all the other parts >>> that are only used for ISA devices, but leaving the actual core >>> (all exported symbols) in this file? >> >> Unfortunately, I don't see a way to remove the stacked initialization >> without risking tons of breakage. >> >> Since later probes can "find" an already-existing port and >> re-initialize it, the probe order is crucial. For example, a PCI >> probe can "find" an existing "serial8250" platform device port, >> resulting in only one device node. > > I'm probably missing something important, by why would that > be any different if the PCI driver gets loaded first and the > ISA driver second? Well, the PCI driver would have the proper irq, for one. So, if the the platform driver re-initialized the port to the wrong irq... >> And the configuration knob will be required on all arches anyway because >> that's how user-configurable device nodes are created. > > I think that's fine: The user-configurable ports are the same as > the "ISA" or "phantom" ports we were talking about above, right? Yes. > If those are part of a separate (possibly loadable) module, having > a configuration knob is the obvious way to do it. A lot of architectures > can just turn it off because they know exactly which ports are present > and there is no need for user-configurability. The ones that don't know > can load the module. Let me give this some more thought. Regards, Peter Hurley