From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C0F9C43219 for ; Thu, 2 May 2019 10:46:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CFA942075E for ; Thu, 2 May 2019 10:46:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726416AbfEBKqC (ORCPT ); Thu, 2 May 2019 06:46:02 -0400 Received: from mga14.intel.com ([192.55.52.115]:20662 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726231AbfEBKqC (ORCPT ); Thu, 2 May 2019 06:46:02 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 02 May 2019 03:46:01 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,421,1549958400"; d="scan'208";a="228622453" Received: from smile.fi.intel.com (HELO smile) ([10.237.72.86]) by orsmga001.jf.intel.com with ESMTP; 02 May 2019 03:45:58 -0700 Received: from andy by smile with local (Exim 4.92) (envelope-from ) id 1hM9Dw-0004MM-M5; Thu, 02 May 2019 13:45:56 +0300 Date: Thu, 2 May 2019 13:45:56 +0300 From: Andy Shevchenko To: Esben Haabendal Cc: linux-serial@vger.kernel.org, Enrico Weigelt , Greg Kroah-Hartman , Jiri Slaby , Darwin Dingel , Jisheng Zhang , Sebastian Andrzej Siewior , He Zhe , Marek Vasut , Douglas Anderson , Paul Burton , linux-kernel@vger.kernel.org Subject: Re: [PATCH] serial: 8250: Add support for using platform_device resources Message-ID: <20190502104556.GS9224@smile.fi.intel.com> References: <20190430140416.4707-1-esben@geanix.com> <20190430153736.GL9224@smile.fi.intel.com> <874l6efxta.fsf@haabendal.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <874l6efxta.fsf@haabendal.dk> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 01, 2019 at 09:17:37AM +0200, Esben Haabendal wrote: > Andy Shevchenko writes: > > Hmm... Currently it's done inside individual port drivers, like 8250_dw.c. > > Each of the drivers can do it differently, for example 8250_lpss.c or > > 8250_pnp.c. > > So, you would prefer to create a new "specialized" port driver that uses > platform resources? I am not doing anything else different from > the generic port driver here in 8250_core.c. If it's required and using serial8250 directly is not enough. > >> + if (!(port->flags & UPF_DEV_RESOURCES)) > >> + release_mem_region(port->mapbase, size); > > > > This is again same issue. The parent should not request resource it > > doesn't use. > > Yes, this is same issue. > > But the last part is not true. A parent mfd driver might "use" a memory > resource for the sole purpose of splitting it up for it's mfd child > devices. This is a core part of mfd framework, and not something I am > inventing with this patch. I am just trying to make it possible to use > 8250 driver in that context. > > > I think I understand what is a confusion here. > > > > For the IO resources we have two operations: > > - mapping / re-mapping (may be shared) > > - requesting (exclusive) > > > > In the parenthesis I put a level of access to it. While many device > > drivers can *share* same resource (mapped or unmapped), the only one > > can actually request it. > > Mostly true. But there is an important twist to the exclusive restriction. > > The exclusive part of the request is limited to the the same root/parent > resource. > > When you request a memory resource from the root resource > (iomem_resource), the resource returned can be used as a new parent > resource. This new parent can then be used to give exclusive access to > slices of that resource. When used like that, I expect that the parent > resource is not supposed to be used for anything else than honoring > resource requests. > > And this is exactly what mfd-core uses the mem_base argument > in mfd_add_devices(). > > > So, the parent can take an slice resources as it would be > > appropriated, but not requesting them. > > The parent is not and should not be doing that by itself. The request > is done on by mfd-core when mfd_add_devices() is called. No, MFD *does not* (and actually *may not* in order to allow standalone drivers to be used as children w/o modifications) request resources. It just passes them to children as parent suggested. > > OTOH, it's possible to have a (weird) MFD case where parent *requested* > > resources, and *all* of its children are aware of that. > > I am not sure what you mean with this, but mfd drivers should not pass > along it's intire requested memory resource(s) to child devices. The > child devices will get the requested resource slices, as implemented by > mfd_add_devices(). > > I hope you can see that I am not violating any fundamental design > decissions here, but actually try adhere to them (resource management, > platform_device resource management, and mfd-core). -- With Best Regards, Andy Shevchenko