Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752168AbdHPPW3 (ORCPT ); Wed, 16 Aug 2017 11:22:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:46366 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751635AbdHPPW0 (ORCPT ); Wed, 16 Aug 2017 11:22:26 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8029822C8D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=robh+dt@kernel.org MIME-Version: 1.0 In-Reply-To: <20170816004238.GH20467@bill-the-cat> References: <1502831736-28282-1-git-send-email-trini@konsulko.com> <599388D0.9050108@gmail.com> <20170816004238.GH20467@bill-the-cat> From: Rob Herring Date: Wed, 16 Aug 2017 10:22:03 -0500 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] devicetree: Enable generation of __symbols__ in all dtb files To: Tom Rini Cc: Frank Rowand , "devicetree@vger.kernel.org" , Tero Kristo , Nishanth Menon , Tomi Valkeinen , Sekhar Nori , Masahiro Yamada , Michal Marek , Pantelis Antoniou , "linux-kernel@vger.kernel.org" , Linux Kbuild mailing list Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2182 Lines: 50 On Tue, Aug 15, 2017 at 7:42 PM, Tom Rini wrote: > On Tue, Aug 15, 2017 at 04:50:40PM -0700, Frank Rowand wrote: >> On 08/15/17 14:15, Tom Rini wrote: >> > With support for stacked overlays being part of libfdt it is now >> > possible and likely that overlays which require __symbols__ will be >> > applied to the dtb files generated by the kernel. This is done by >> > passing -@ to dtc. This does increase the filesize (and resident memory >> > usage) based on the number of __symbol__ entries added to match the >> > contents of the dts. >> > >> > Cc: Rob Herring >> > Cc: Frank Rowand >> > Cc: Masahiro Yamada >> > Cc: Michal Marek >> > Cc: Pantelis Antoniou >> > Cc: devicetree@vger.kernel.org >> > Cc: linux-kernel@vger.kernel.org >> > CC: linux-kbuild@vger.kernel.org >> > Signed-off-by: Tom Rini >> > --- >> > In order for a dtb file to be useful with all types of overlays, it >> > needs to be generated with the -@ flag passed to dtc so that __symbols__ >> > are generated. This however is not free, and increases the resulting >> > dtb file by up to approximately 50% today. In the current worst case >> > this is moving from 88KiB to 133KiB. In talking with Frank about this, >> > he outlined 3 possible ways (with the 4th option of something else >> > entirely). >> > >> > 1. Make passing -@ to dtc be dependent upon some CONFIG symbol. >> > 2. In the kernel, if the kernel does not have overlay support, discard >> > the __symbols__ information that we've been passed. >> > 3. Have the bootloader pass in, or not, __symbols__ information. >> >> I also was hoping that other people might have ideas for additional >> approaches. > > Yes, please. A couple of other options come to mind: "make DTC_FLAGS='-@' dtbs" should already work. So there's already a way to build what you want and the kernel is not setting the policy. Do like we do for the unittests and make it a per board decision: DTC_FLAGS_my-som-board.dtb := -@ Then boards that actually need it like SoMs can turn it on. Rob