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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7012C6FA8B for ; Tue, 6 Sep 2022 15:22:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239251AbiIFPWB (ORCPT ); Tue, 6 Sep 2022 11:22:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39106 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234950AbiIFPVh (ORCPT ); Tue, 6 Sep 2022 11:21:37 -0400 Received: from sibelius.xs4all.nl (80-61-163-207.fixed.kpn.net [80.61.163.207]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A3E4E98370; Tue, 6 Sep 2022 07:33:36 -0700 (PDT) Received: from localhost (bloch.sibelius.xs4all.nl [local]) by bloch.sibelius.xs4all.nl (OpenSMTPD) with ESMTPA id c29ccd8f; Tue, 6 Sep 2022 16:25:49 +0200 (CEST) Date: Tue, 6 Sep 2022 16:25:49 +0200 (CEST) From: Mark Kettenis To: Hector Martin Cc: linux@armlinux.org.uk, linus.walleij@linaro.org, robh@kernel.org, krzysztof.kozlowski@linaro.org, arnd@arndb.de, lee@kernel.org, alyssa@rosenzweig.io, asahi@lists.linux.dev, brgl@bgdev.pl, linux-arm-kernel@lists.infradead.org, linux-gpio@vger.kernel.org, sven@svenpeter.dev, krzysztof.kozlowski+dt@linaro.org, devicetree@vger.kernel.org In-Reply-To: (message from Hector Martin on Tue, 6 Sep 2022 22:53:47 +0900) Subject: Re: [PATCH 1/6] dt-bindings: mfd: add binding for Apple Mac System Management Controller References: <20220902172808.GB52527-robh@kernel.org> <909bb4e7-5bd2-2903-5bba-87ae37f3448a@marcan.st> <5b75dc7e-5337-73eb-450f-b72f479793c4@marcan.st> Message-ID: Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org > Date: Tue, 6 Sep 2022 22:53:47 +0900 > From: Hector Martin > > On 06/09/2022 22.43, Russell King (Oracle) wrote: > > In the case of gpio-macsmc, how would we later add support for the > > slave PMU GPIOs, given that these use keys "gpXX" rather than "gPxx"? > > How do we tell the gpio-macsmc code to use a different set of keys? > > Should DT describe the key "prefix" (in other words "gp" vs "gP"), > > or should it describe it some other way. What if Apple decides to > > instantiate another GPIO controller in a later platform with a > > different prefix, could that be accomodated without breaking any > > solution we come up today? > > > > Maybe the solution to this would be to describe the key prefix in DT > > as that's effectively its "reg". Or maybe we use "reg" to describe > > it somehow (which is value of the key, which seems to have an > > "address" like quality to it?) > > > > We don't have to implement code for this now, we just need to get a > > reasonably correct DT binding for the gpio controller. > > I agree that this is something to think about (I was about to reply on > the subject). > > I can think of two ways: using `reg` for the key name, but that feels > icky since it's ASCII and not *really* a register number/address, or > something like this: > > gpio@0 { > apple,smc-key-base = "gP00"; > ... > } > > gpio@1 { > apple,smc-key-base = "gp00"; > ... > } This would still require us to add a (one-cell) "reg" property and would require adding the appropriate "#address-cells" and "#size-cells" properties to the SMC node. > But this ties back to the device enumeration too, since right now the DT > does not drive that (we'd have to add the subdevice to the mfd subdevice > list somehow anyway, if we don't switch to compatibles). > > I'd love to hear Rob's opinion on this one, and also whether the > existing Linux and OpenBSD code would currently find gpio@0 {} instead > of gpio {} for backwards compat. The OpenBSD driver does a lookup by name and the "@0" is part of that name. So that would break backwards compat. Maybe just name the slave GPIO controller "gpio-slave"? If we add compatibles, the compatibles for the nodes should propbably be different such that we can switch to do a lookup by compatible?