From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755115Ab3KURtM (ORCPT ); Thu, 21 Nov 2013 12:49:12 -0500 Received: from mail-pb0-f53.google.com ([209.85.160.53]:56687 "EHLO mail-pb0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755085Ab3KURtJ (ORCPT ); Thu, 21 Nov 2013 12:49:09 -0500 MIME-Version: 1.0 In-Reply-To: <20131121155348.66751C406A3@trevor.secretlab.ca> References: <5283A000.8090007@gmail.com> <20131121155348.66751C406A3@trevor.secretlab.ca> Date: Thu, 21 Nov 2013 18:49:08 +0100 X-Google-Sender-Auth: tM8La1LAe0E_nrb8_RbnJt2ta90 Message-ID: Subject: Re: [PATCH 1/9] dt: Handle passed/built-in DT selection in early_init_dt_scan() From: Geert Uytterhoeven To: Grant Likely Cc: Rob Herring , "devicetree@vger.kernel.org" , Linux-Arch , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 21, 2013 at 4:53 PM, Grant Likely wrote: >> My changes don't change the current behavior much: currently >> early_init_dt_scan() is already called with &__dtb_start in several places. >> If this is broken, it's already broken. > > Yes, but it is called on platforms that already make that assumption > that __dtb_start must be copied and therefore call > unflatten_and_copy_devicetree(). This change makes *all* platforms do > that. That breaks arm, arm64, c6x, microblaze, some mips platforms, and > powerpc! arm, arm64, and powerpc don't have builtin DTBs, hence no change. microblaze and c6x already did "early_init_devtree(&__dtb_start)" before. That leaves mips, which has DT handling in too many variants, which I didn't all verify. >> > memory. The dtb section can also potentially contain multiple .dtb >> > blobs. In the use case that you care about you are probably only >> >> Multiple dtb blobs are currently handled in platform-specific code, which >> passes the right dtb to early_init_dt_scan(). > > The problem is that it makes the default dt completely random because > the generic code still deferrences __dtb_start. Only if no DT was passed by the bootloader. And only if there really is something at __dtb_start. Before it would fail if no DTB was passed by the bootloader. >> > thinking about one, but it is entirely possible for device drivers to >> > have a dtb linked in which may break this if it gets linked in a >> > different order. The specific example I'm thinking about is I want to >> > have the DT selftest code load an overlay to get testcase data from a >> > dtb blob. >> > >> > The other concern I have here is that I don't really want this to be the >> > default on a lot of platforms. ARM and PowerPC for instance should only >> > get the default dtb from the boot wrapper. It needs to be configurable >> > in some way. >> >> On ARM and PowerPC, the section is empty, hence &__dbt_start == >> &__dtb_end. > > There is no guarantee that that will always be so. The patch makes some > poor assumtions, but they shouldn't be difficult to fix. OK, how to proceed? Thanks! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds