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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 D426BC83000 for ; Tue, 28 Apr 2020 13:06:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ABB6C206D6 for ; Tue, 28 Apr 2020 13:06:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726870AbgD1NG0 (ORCPT ); Tue, 28 Apr 2020 09:06:26 -0400 Received: from foss.arm.com ([217.140.110.172]:51134 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726746AbgD1NG0 (ORCPT ); Tue, 28 Apr 2020 09:06:26 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 145BA31B; Tue, 28 Apr 2020 06:06:25 -0700 (PDT) Received: from [10.57.33.170] (unknown [10.57.33.170]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 710363F68F; Tue, 28 Apr 2020 06:06:21 -0700 (PDT) Subject: Re: [PATCH v3 02/16] mfd: mfd-core: Don't overwrite the dma_mask of the child device To: Andy Shevchenko , Michael Walle Cc: linux-gpio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-pwm@vger.kernel.org, linux-watchdog@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Linus Walleij , Bartosz Golaszewski , Rob Herring , Jean Delvare , Guenter Roeck , Lee Jones , Thierry Reding , =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= , Wim Van Sebroeck , Shawn Guo , Li Yang , Thomas Gleixner , Jason Cooper , Marc Zyngier , Mark Brown , Greg Kroah-Hartman References: <20200423174543.17161-1-michael@walle.cc> <20200423174543.17161-3-michael@walle.cc> <20200428124548.GS185537@smile.fi.intel.com> From: Robin Murphy Message-ID: <3cd3705a-4f48-6a46-e869-3ee11dc17323@arm.com> Date: Tue, 28 Apr 2020 14:06:20 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200428124548.GS185537@smile.fi.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-hwmon-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org On 2020-04-28 1:45 pm, Andy Shevchenko wrote: > On Thu, Apr 23, 2020 at 07:45:29PM +0200, Michael Walle wrote: >> Commit cdfee5623290 ("driver core: initialize a default DMA mask for >> platform device") initialize the DMA of a platform device. But if the >> parent doesn't have a dma_mask set, for example if it's an I2C device, >> the dma_mask of the child platform device will be set to zero again. >> Which leads to many "DMA mask not set" warnings, if the MFD cell has the >> of_compatible property set. > > I'm wondering why parent doesn't have it. Because the parent isn't on a DMA-capable bus, and thus really shouldn't have a valid DMA configuration ever. > I remember we have explicit patches in the past for buses such as PCI and AMBA > to set default DMA mask for all physical devices on the respective bus, of > course they can individually override it later. > > So, this seems to me a paper over the real issue (absence of default DMA mask > where it's needed) and devices should explicitly define it if they disagree > with default. > > If I'm wrong, you really need elaborate commit message much better. The problem here is that MFD children are created as platform devices (regardless of what their parent is) and assigned an of_node, at which point they look pretty much indistinguishable from SoC devices created by the of_platform code, that *do* have to be assumed to be DMA-capable to prevent ~90% of existing devicetrees from breaking. Of course the real fundamental issue is the platform bus itself, but it's way too late to fix that :( Robin.