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 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 B78D9C433E3 for ; Mon, 8 Jun 2020 15:41:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 88D852076C for ; Mon, 8 Jun 2020 15:41:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=walle.cc header.i=@walle.cc header.b="Bi0kBxLj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730349AbgFHPlz (ORCPT ); Mon, 8 Jun 2020 11:41:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53496 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730237AbgFHPly (ORCPT ); Mon, 8 Jun 2020 11:41:54 -0400 Received: from ssl.serverraum.org (ssl.serverraum.org [IPv6:2a01:4f8:151:8464::1:2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0E018C08C5C2; Mon, 8 Jun 2020 08:41:54 -0700 (PDT) Received: from ssl.serverraum.org (web.serverraum.org [172.16.0.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ssl.serverraum.org (Postfix) with ESMTPSA id AFD1C22EDB; Mon, 8 Jun 2020 17:41:51 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=walle.cc; s=mail2016061301; t=1591630912; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=etHTaFe1EeC9mBKvG6HTofjnIp6HCeqLDPf5/dR8kqA=; b=Bi0kBxLjCYDjn9gKsxm1WK1dR/X+gTRDxY4SHRyL5qu5dMnITfQG2NTYcKF7lHNWy1f3+x PkWD9sdh/ko4F6iRWIvyIA52MxvjMFHrzOjFsYWggFruJSQgbowUgvkjVjmiTO9OZZsjoW yW+vV7MAFPS4Ms8LjJg5r/ni8YX5+Kk= MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Mon, 08 Jun 2020 17:41:51 +0200 From: Michael Walle To: Andy Shevchenko Cc: Lee Jones , Ranjani Sridharan , david.m.ertman@intel.com, shiraz.saleem@intel.com, Rob Herring , Mark Brown , "open list:GPIO SUBSYSTEM" , devicetree , Linux Kernel Mailing List , linux-hwmon@vger.kernel.org, linux-pwm@vger.kernel.org, linux-watchdog@vger.kernel.org, linux-arm Mailing List , Linus Walleij , Bartosz Golaszewski , Jean Delvare , Guenter Roeck , Thierry Reding , =?UTF-8?Q?Uwe_Kleine-K?= =?UTF-8?Q?=C3=B6nig?= , Wim Van Sebroeck , Shawn Guo , Li Yang , Thomas Gleixner , Jason Cooper , Marc Zyngier , Greg Kroah-Hartman , Andy Shevchenko Subject: Re: [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller In-Reply-To: References: <20200604211039.12689-1-michael@walle.cc> <20200604211039.12689-3-michael@walle.cc> <20200605065709.GD3714@dell> <20200605105026.GC5413@sirena.org.uk> <20200606114645.GB2055@sirena.org.uk> <20200608082827.GB3567@dell> User-Agent: Roundcube Webmail/1.4.4 Message-ID: <7d7feb374cbf5a587dc1ce65fc3ad672@walle.cc> X-Sender: michael@walle.cc Sender: linux-watchdog-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-watchdog@vger.kernel.org Am 2020-06-08 12:02, schrieb Andy Shevchenko: > +Cc: some Intel people WRT our internal discussion about similar > problem and solutions. > > On Mon, Jun 8, 2020 at 11:30 AM Lee Jones wrote: >> On Sat, 06 Jun 2020, Michael Walle wrote: >> > Am 2020-06-06 13:46, schrieb Mark Brown: >> > > On Fri, Jun 05, 2020 at 10:07:36PM +0200, Michael Walle wrote: >> > > > Am 2020-06-05 12:50, schrieb Mark Brown: > > ... > >> Right. I'm suggesting a means to extrapolate complex shared and >> sometimes intertwined batches of register sets to be consumed by >> multiple (sub-)devices spanning different subsystems. >> >> Actually scrap that. The most common case I see is a single Regmap >> covering all child-devices. > > Yes, because often we need a synchronization across the entire address > space of the (parent) device in question. > >> It would be great if there was a way in >> which we could make an assumption that the entire register address >> space for a 'tagged' (MFD) device is to be shared (via Regmap) between >> each of the devices described by its child-nodes. Probably by picking >> up on the 'simple-mfd' compatible string in the first instance. >> >> Rob, is the above something you would contemplate? >> >> Michael, do your register addresses overlap i.e. are they intermingled >> with one another? Do multiple child devices need access to the same >> registers i.e. are they shared? No they don't overlap, expect for maybe the version register, which is just there once and not per function block. >> >> > > > But, there is more in my driver: >> > > > (1) there is a version check >> >> If we can rid the Regmap dependency, then creating an entire driver to >> conduct a version check is unjustifiable. This could become an inline >> function which is called by each of the sub-devices instead, for >> example. sounds good to me. (although there would then be a probe fail per sub-device if the version is not supported) >> > > > (2) there is another function for which there is no suitable linux >> > > > subsystem I'm aware of and thus which I'd like to us sysfs >> > > > attributes for: This controller supports 16 non-volatile >> > > > configuration bits. (this is still TBD) >> >> There is a place for everything in Linux. >> >> What do these bits configure? - hardware strappings which have to be there before the board powers up, like clocking mode for different SerDes settings - "keep-in-reset" bits for onboard peripherals if you want to save power - disable watchdog bits (there is a watchdog which is active right from the start and supervises the bootloader start and switches to failsafe mode if it wasn't successfully started) - special boot modes, like eMMC, etc. Think of it as a 16bit configuration word. >> > > TBH I'd also say that the enumeration of the subdevices for this >> > > device should be in the device rather than the DT, they don't >> > > seem to be things that exist outside of this one device. >> > >> > We're going circles here, formerly they were enumerated in the MFD. >> > Yes, they are devices which aren't likely be used outside a >> > "sl28cpld", but there might there might be other versions of the >> > sl28cpld with other components on different base addresses. I >> > don't care if they are enumerated in DT or MFD, actually, I'd >> > prefer the latter. _But_ I would like to have the device tree >> > properties for its subdevices, e.g. the ones for the watchdog or >> > whatever components there might be in the future. >> >> [...] >> >> > MFD core can >> > match a device tree node today; but only one per unique compatible >> > string. So what should I use to differentiate the different >> > subdevices? >> >> Right. I have been aware of this issue. The only suitable solution >> to this would be to match on 'reg'. see below (1) >> >> FYI: I plan to fix this. >> >> If your register map needs to change, then I suggest that this is >> either a new device or at least a different version of the device and >> would also have to be represented as different (sub-)mfd_cell. >> >> > Rob suggested the internal offset, which I did here. >> >> FWIW, I don't like this idea. DTs should not have to be modified >> (either in the first instance or subsequently) or specifically >> designed to patch inadequacies in any given OS. How does (1) play together with this? What do you propose the "reg" property should contain? >> >> > But then, there is less use in duplicating the offsets in the MFD >> > just to have the MFD enumerate the subdevices and then match >> > the device tree nodes against it. I can just use >> > of_platform_populate() to enumerate the children and I won't >> > have to duplicate the base addresses. >> >> Which is fine. However this causes a different issue for you. By >> stripping out the MFD code you render the MFD portion seemingly >> superfluous. Another issue driver authors commonly contend with. Yeah, I agree. -michael