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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 284C1C282DA for ; Sat, 6 Apr 2019 06:07:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EDD2C21855 for ; Sat, 6 Apr 2019 06:07:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1554530843; bh=KsrQE2MTBp3bk98l3KOK/flwpZegAQ2o0wmrUkaT1qk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=FCtd2oBnXH0QADwZIAHahDiKf3uZ9dcuiBWZo7MHhdqNWxLZ4O9/GEUs2XL64kFXp +6kNax2+hoWjin/Gsw89Ubjwl5D3p4ROyDBguVn0IFcqbHrqM+HQfnw21+vBP7X0w1 QDfgVicm/0Myl9kB7VYUHYg28cEja8m/4w21Q88c= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726921AbfDFGHV (ORCPT ); Sat, 6 Apr 2019 02:07:21 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:42789 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725290AbfDFGHU (ORCPT ); Sat, 6 Apr 2019 02:07:20 -0400 Received: by mail-pg1-f196.google.com with SMTP id p6so4190851pgh.9; Fri, 05 Apr 2019 23:07:20 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:message-id:date:from:to:cc:subject:references :mime-version:content-disposition:in-reply-to; bh=CrDN3pSofWfhjPsMJgky5ErEeSo4CNJyaPHKeeJSTRE=; b=L6lyTRkthYY743tKivdLDTH2ckQc1NJTWFNJ5htLeYt4ry5l5eTSjE1nY5cmqncVi3 wc2GdnSd/eujdIdHgKbNCPqiGHV212ytIneFA3ipexxoAagtJ5kzFZeM1TXLvWubTutV nYAWAiBplJ3NN0kOq5ZqNBOxcGgMHRO1DsuxoU63JgSenqrKg6UrgvzmTFv9Hix50wX2 Qo7GyPNigTt3NUDshse+moLETdeu6PCP0eu+FmiP0ZiiTcV/qdEXP1VfztuLOzEm+RyJ tv+E00GuUTLfU8YwNbjxx8nXOwMpHRFLawezBeuNoeFHDhr74p8uk+XeduFLt/49nvis Ue1g== X-Gm-Message-State: APjAAAXaeqV27JMB14AEWFdf6lp04+RZJWxkyiuFY8JeiPVIaUt+ipME 8Mon5xqN9oVE9JSVxlCYgQ== X-Google-Smtp-Source: APXvYqy4GAsrJVsherGMBDLhOFGl5ut5+YkFmH6wbcv+3GV2SAxFqxzf+b7mgrWEcTE/wH7jQ3L5NA== X-Received: by 2002:a63:9dc4:: with SMTP id i187mr15185563pgd.259.1554530839480; Fri, 05 Apr 2019 23:07:19 -0700 (PDT) Received: from localhost ([210.160.217.71]) by smtp.gmail.com with ESMTPSA id l88sm41573983pfb.104.2019.04.05.23.07.18 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 05 Apr 2019 23:07:18 -0700 (PDT) Message-ID: <5ca84216.1c69fb81.3205c.592c@mx.google.com> Date: Sat, 06 Apr 2019 01:07:16 -0500 From: Rob Herring To: Chris Packham Cc: "pantelis.antoniou@konsulko.com" , "frowand.list@gmail.com" , "devicetree@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Hamish Martin Subject: Re: Using device tree overlays in Linux References: <71fb0ff289e84c55bd92ecd96bc9aa76@svr-chch-ex1.atlnz.lc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <71fb0ff289e84c55bd92ecd96bc9aa76@svr-chch-ex1.atlnz.lc> X-Mutt-References: <71fb0ff289e84c55bd92ecd96bc9aa76@svr-chch-ex1.atlnz.lc> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 04, 2019 at 01:50:20AM +0000, Chris Packham wrote: > Hi, > > I'm implementing support for some modular Linux based systems using > device tree overlays. The code is working but it seems a little more > fiddly that than it should be so I'm wondering if I'm doing it right. > > An example of what I'm doing is > > > arch/arm/boot/dts/Makefile: > DTC_FLAGS_myboard += -@ > > drivers/foo/Makefile: > obj-y += myplugin.dtb.o > obj-y += mydriver.o > > drivers/foo/myplugin.dts: > /dts-v1/; > /plugin/; > /{ > fragment@0 { > target = <&i2c0>; > __overlay__ { > gpio@74 { > compatible = "nxp,pca9539"; > reg = <0x74> > }; > }; > }; > }; > > drivers/foo/mydriver.c: > extern uint8_t __dtb_myplugin_begin[]; > extern uint8_t __dtb_myplugin_end[]; > > int mydriver_probe(struct platform_device *pdev) > { > u32 size = __dtb_myplugin_end - __dtb_myplugin_begin; > int overlay_id; > int ret; > > ret = of_overlay_fdt_apply(__dtb_myplugin_begin, > size, &overlay_id); > return ret; > } > > > The first issue is that I need to add -@ to the DTC_FLAGS for my board > dtb. I kind of understand that I only need -@ if my overlay targets > something symbolic so I might not need it but I was surprised that there > wasn't a Kconfig option that makes this happen automatically. Whether overlays make sense or are needed are per board. You could add a kconfig entry that drivers which depend on overlays select, but turning on '-@' has to be per board (or SoC family if the SoC maintainer is okay with that). > externing things in C files makes checkpatch.pl complain. I see the > of/unittests.c and rcar_du_of.c hide this with a macro. I was again > surprised that there wasn't a common macro to declare these. Feel free to propose something. There just aren't that many cases that anyone has cared what checkpatch says. Rob