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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 32BA2C433DF for ; Tue, 9 Jun 2020 19:05:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0F0AE206C3 for ; Tue, 9 Jun 2020 19:05:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="YzCXPlKz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730592AbgFITEv (ORCPT ); Tue, 9 Jun 2020 15:04:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53002 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730506AbgFITEu (ORCPT ); Tue, 9 Jun 2020 15:04:50 -0400 Received: from mail-wm1-x343.google.com (mail-wm1-x343.google.com [IPv6:2a00:1450:4864:20::343]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A71A4C08C5C3 for ; Tue, 9 Jun 2020 12:04:49 -0700 (PDT) Received: by mail-wm1-x343.google.com with SMTP id l26so3845206wme.3 for ; Tue, 09 Jun 2020 12:04:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to; bh=Ge3VyoAaZL1/OTneZ+2zUT+PtoEIvR18KepPJWadg9c=; b=YzCXPlKztl5CJV/qwyuSuukBnUr3e+8KLSfzl0TTqnV1Tbrsyld6tNRKD3PrQoU0l9 Sa5fTQ6+C9sRbTX2XaHSoLR1M6k97ZiNwg4wPy8nTgzHmiS6XNuh6V5W6g0utgMwljM5 rzYxOOFmojUpgjLWDRYm6IUeSOsSK+AWPgs4xw9KocaDbKG0yrMIKJJzm2GUeOkmN2Zc kPZljWf/OGSNTRpZJveKQDz5RY+4kFNQNIWjdAb7CZtH+rcPNb6BOf6lC13G7R7mCGEk h5F9TxveHrq1CUWDceH9H+nZ/cLOxU0xOILATOaRfuJRqTysFIz3kwn7j5rR1F494h5I Ukdg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=Ge3VyoAaZL1/OTneZ+2zUT+PtoEIvR18KepPJWadg9c=; b=gtafTH5XAwvaCsruD8ZwqANzQ+M8abEkDR4itCR/TkVqxgZn8+/MWeJDoFqwhOpIhD rWCfsOTsU1QyaCOu4duAeAyodxv4uqIU/i6yVr4QfJylJ8Qr3uBns7n1mr0XGBWGQ9lh J8zWQnm8qazuv2st8XPWikZHXUAa5nj4oO9dnoPX1qWnsqUhalWF9K1xI9pUcV5ym4kR 4Zvfzkki8l3hR/6EmtdImhh2+afI6mwhyMxHC01mMx+dHw8OLR6PsZdVso8F6TUJ5IzC rKzkcWaqxtykDER126Tpu0knJQw+bSihLzHgQT04wvB0DPQzS2/c7wUDhgHVhsQs4omI BroQ== X-Gm-Message-State: AOAM533RVAPkZyVg/+fVmv6AFiD6Xi4BUuNyQbDVcpjhzbtFvoQ4DIGk mbPYaqeNqL24+xm/JIINxwAJFw== X-Google-Smtp-Source: ABdhPJzN+BygjHAXONePT0Kf4YAs7yH6hesdbbYDOCsdr+huL8ukQ34b+ZD+otUf+KiEJ7FWdD9eJA== X-Received: by 2002:a7b:ce88:: with SMTP id q8mr5410226wmj.176.1591729488213; Tue, 09 Jun 2020 12:04:48 -0700 (PDT) Received: from dell ([2.27.167.101]) by smtp.gmail.com with ESMTPSA id g25sm3794436wmh.18.2020.06.09.12.04.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Jun 2020 12:04:46 -0700 (PDT) Date: Tue, 9 Jun 2020 20:04:45 +0100 From: Lee Jones To: Andy Shevchenko Cc: Michael Walle , Rob Herring , Mark Brown , devicetree , Linux Kernel Mailing List , linux-arm Mailing List , Linus Walleij , Guenter Roeck , Andy Shevchenko , Robin Murphy , GregKroah-Hartmangregkh@linuxfoundation.org Subject: Re: [RFC] MFD's relationship with Device Tree (OF) Message-ID: <20200609190445.GP4106@dell> References: <20200609110136.GJ4106@dell> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Tue, 09 Jun 2020, Andy Shevchenko wrote: > On Tue, Jun 9, 2020 at 2:01 PM Lee Jones wrote: > > > > Good morning, > > > > After a number of reports/queries surrounding a known long-term issue > > in the MFD core, including the submission of a couple of attempted > > solutions, I've decided to finally tackle this one myself. > > > > Currently, when a child platform device (sometimes referred to as a > > sub-device) is registered via the Multi-Functional Device (MFD) API, > > the framework attempts to match the newly registered platform device > > with its associated Device Tree (OF) node. Until now, the device has > > been allocated the first node found with an identical OF compatible > > string. Unfortunately, if there are, say for example '3' devices > > which are to be handled by the same driver and therefore have the same > > compatible string, each of them will be allocated a pointer to the > > *first* node. > > > > Let me give you an example. > > > > I have knocked up an example 'parent' and 'child' device driver. The > > parent utilises the MFD API to register 3 identical children, each > > controlled by the same driver. This happens a lot. Fortunately, in > > the majority of cases, the OF nodes are also totally identical, but > > what if you wish to configure one of the child devices with different > > attributes or resources supplied via Device Tree, like a clock? This > > is currently impossible. > > > > Here is the Device Tree representation for the 1 parent and the 3 > > child (sub) devices described above: > > > > parent { > > compatible = "mfd,of-test-parent"; > > > > child@0 { > > compatible = "mfd,of-test-child"; > > clocks = <&clock 0>; > > }; > > > > child@1 { > > compatible = "mfd,of-test-child"; > > clocks = <&clock 1>; > > }; > > > > child@2 { > > compatible = "mfd,of-test-child"; > > clocks = <&clock 2>; > > }; > > }; > > > > This is how we register those devices from MFD: > > > > static const struct mfd_cell mfd_of_test_cell[] = { > > OF_MFD_CELL("mfd_of_test_child", NULL, NULL, 0, 0, "mfd,of-test-child"), > > OF_MFD_CELL("mfd_of_test_child", NULL, NULL, 0, 1, "mfd,of-test-child"), > > OF_MFD_CELL("mfd_of_test_child", NULL, NULL, 0, 2, "mfd,of-test-child") > > }; > > > > ... which we pass into mfd_add_devices() for processing. > > > > In an ideal world. The devices with the platform_id; 0, 1 and 2 would > > be matched up to Device Tree nodes; child@0, child@1 and child@2 > > respectively. Instead all 3 devices will be allocated a pointer to > > child@0's OF node, which is obviously not correct. > > > > This is how it looks when each of the child devices are probed: > > > > [0.708287] mfd-of-test-parent mfd_of_test: Registering 3 devices > > [...] > > [0.712511] mfd-of-test-child mfd_of_test_child.0: Probing platform device: 0 > > [0.712710] mfd-of-test-child mfd_of_test_child.0: Using OF node: child@0 > > [0.713033] mfd-of-test-child mfd_of_test_child.1: Probing platform device: 1 > > [0.713381] mfd-of-test-child mfd_of_test_child.1: Using OF node: child@0 > > [0.713691] mfd-of-test-child mfd_of_test_child.2: Probing platform device: 2 > > [0.713889] mfd-of-test-child mfd_of_test_child.2: Using OF node: child@0 > > > > "Why is it when I change child 2's clock rate, it also changes 0's?" > > > > Whoops! > > > > So in order to fix this, we need to make MFD more-cleverer! > > > > However, this is not so simple. There are some rules we should abide > > by (I use "should" intentionally here, as something might just have to > > give): > > > > a) Since Device Tree is designed to describe hardware, inserting > > arbitrary properties into DT is forbidden. This precludes things > > we would ordinarily be able to match on, like 'id' or 'name'. > > b) As an extension to a) DTs should also be OS agnostic, so > > properties like 'mfd-device', 'mfd-order' etc are also not > > not suitable for inclusion. > > c) The final solution should ideally be capable of supporting both > > newly defined and current trees (without retroactive edits) > > alike. > > d) Existing properties could be used, but not abused. For example, > > one of my suggestions (see below) is to use the 'reg' property. > > This is fine in principle but loading 'reg' with arbitrary values > > (such as; 0, 1, 2 ... x) which 1) clearly do not have anything to > > do with registers and 2) would be meaningless in other OSes/ > > implementations, just to serve our purpose, is to be interpreted > > as an abuse. > > > > Proposal 1: > > > > As mentioned above, my initial thoughts were to use the 'reg' property > > to match an MFD cell entry with the correct DT node. However, not > > all Device Tree nodes have 'reg' properties. Particularly true in the > > case of MFD, where memory resources are usually shared with the parent > > via Regmap, or (as in the case of the ab8500) the MFD handles all > > register transactions via its own API. > > > > Proposal 2: > > > > If we can't guarantee that all DT nodes will have at least one > > property in common to be used for matching and we're prevented from > > supplying additional, potentially bespoke properties, then we must > > seek an alternative procedure. > > > > It should be possible to match based on order. However, the developer > > would have to guarantee that the order in which the child devices are > > presented to the MFD API are in exactly the same order as they are > > represented in the Device Tree. The obvious draw-back to this > > strategy is that it's potentially very fragile. > > > > Current Proposal: > > > > How about a collection of Proposal 1 and Proposal 2? First we could > > attempt a match on the 'reg' property. Then, if that fails, we would > > use the fragile-but-its-all-we-have Proposal 2 as the fall-back. > > > > Thoughts? > > Just a side note, have you considered software nodes on the picture? > You can add properties or additional references to the existing > (firmware) nodes. Is that the properties framework you are trying to replace? Is that different to placing additional attributes into pdata? Using my clock example above, how would one allocate a DT based clock to a child device using properties? -- Lee Jones [李琼斯] Senior Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog