From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753138Ab3KUMds (ORCPT ); Thu, 21 Nov 2013 07:33:48 -0500 Received: from mail-ie0-f175.google.com ([209.85.223.175]:50552 "EHLO mail-ie0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750976Ab3KUMdq (ORCPT ); Thu, 21 Nov 2013 07:33:46 -0500 MIME-Version: 1.0 In-Reply-To: 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 12:33:26 +0000 X-Google-Sender-Auth: tu1sEkHhTMchwy476vi-Y08l1GU 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 12:23 PM, Grant Likely wrote: > 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. Okay, I've got one more comment on this. I know that some architectures use unflatten_and_copy_devicetree() to sort out the dtb copy problem. My point here is that for this to become generic code then early_init_dt_scan() needs to grow the ability to differentiate between a DT that needs to be copied (built in) vs. a DT that is already in safe memory. The contents of unflatten_and_copy_devicetree() could even be rolled into unflatten_devicetree() if there is a common way to indicate whether or not the DT needs to be copied that early_init_dt_scan() can manipulate. ie. a global flag. g.