From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754095Ab3KUMYH (ORCPT ); Thu, 21 Nov 2013 07:24:07 -0500 Received: from mail-ie0-f171.google.com ([209.85.223.171]:64153 "EHLO mail-ie0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753443Ab3KUMYF (ORCPT ); Thu, 21 Nov 2013 07:24:05 -0500 MIME-Version: 1.0 In-Reply-To: <20131121122148.1B43DC40A2C@trevor.secretlab.ca> References: <5283A000.8090007@gmail.com> <1384859554-27268-1-git-send-email-geert@linux-m68k.org> <20131121122148.1B43DC40A2C@trevor.secretlab.ca> From: Grant Likely Date: Thu, 21 Nov 2013 12:23:44 +0000 X-Google-Sender-Auth: wwh2uqINQWyw-RV1TEqMmaeOVwY Message-ID: Subject: Re: [PATCH 1/9] dt: Handle passed/built-in DT selection in early_init_dt_scan() To: Geert Uytterhoeven , Rob Herring Cc: "devicetree@vger.kernel.org" , "linux-arch@vger.kernel.org" , Linux Kernel Mailing List Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 21, 2013 at 12:21 PM, Grant Likely wrote: > On Tue, 19 Nov 2013 12:12:26 +0100, Geert Uytterhoeven wrote: >> Let early_init_dt_scan() fall-back to the built-in DT if no DT was passed, >> or if it's invalid, so architectures don't have to duplicate this logic. >> >> Suggested-by: Rob Herring >> Signed-off-by: Geert Uytterhoeven >> --- >> drivers/of/fdt.c | 24 +++++++++++++++++------- >> include/linux/of_fdt.h | 1 + >> 2 files changed, 18 insertions(+), 7 deletions(-) >> >> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c >> index 2fa024b97c43..a797cd43bc8b 100644 >> --- a/drivers/of/fdt.c >> +++ b/drivers/of/fdt.c >> @@ -868,18 +868,28 @@ void * __init __weak early_init_dt_alloc_memory_arch(u64 size, u64 align) >> >> bool __init early_init_dt_scan(void *params) >> { >> - if (!params) >> - return false; >> - >> /* Setup flat device-tree pointer */ >> initial_boot_params = params; >> >> - /* check device tree validity */ >> - if (be32_to_cpu(initial_boot_params->magic) != OF_DT_HEADER) { >> - initial_boot_params = NULL; >> - return false; >> + /* check passed device tree validity */ >> + if (initial_boot_params && >> + be32_to_cpu(initial_boot_params->magic) == OF_DT_HEADER) { >> + pr_info("FDT at %p\n", initial_boot_params); >> + goto found; >> + } >> + >> + /* check built-in device tree validity */ >> + initial_boot_params = &__dtb_start; >> + if (__dtb_end != (void *)&__dtb_start && >> + be32_to_cpu(initial_boot_params->magic) == OF_DT_HEADER) { >> + pr_info("Compiled-in FDT at %p\n", initial_boot_params); >> + goto found; > > __dtb_start is in an init section which is discarded after initcalls. > For this to work, the dtb needs to be copied into a region of allocated > memory. The dtb section can also potentially contain multiple .dtb > blobs. In the use case that you care about you are probably only > 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. > > Instead of using __dtb_start, it would probably solve both of the above > problems if the build-in DTB has a specific label identifying it as the > default DT. Er, not quite. It still doesn't solve the init section discard problem. That still needs solving. g.