From patchwork Tue Sep 25 14:56:01 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Thomas Renninger X-Patchwork-Id: 1504721 Return-Path: X-Original-To: patchwork-linux-acpi@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by patchwork2.kernel.org (Postfix) with ESMTP id DAFF4DF24C for ; Tue, 25 Sep 2012 14:57:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756685Ab2IYO5E (ORCPT ); Tue, 25 Sep 2012 10:57:04 -0400 Received: from cantor2.suse.de ([195.135.220.15]:38686 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755950Ab2IYO43 (ORCPT ); Tue, 25 Sep 2012 10:56:29 -0400 Received: from relay2.suse.de (unknown [195.135.220.254]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mx2.suse.de (Postfix) with ESMTP id A054BA41E0; Tue, 25 Sep 2012 16:56:26 +0200 (CEST) From: Thomas Renninger To: hpa@zytor.com Cc: lenb@kernel.org, initramfs@vger.kernel.org, robert.moore@intel.com, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, yinghai@kernel.org, Thomas Renninger Subject: [PATCH 6/6] ACPI: Document ACPI table overriding via initrd Date: Tue, 25 Sep 2012 16:56:01 +0200 Message-Id: <1348584961-1476-7-git-send-email-trenn@suse.de> X-Mailer: git-send-email 1.7.6.1 In-Reply-To: <1348584961-1476-1-git-send-email-trenn@suse.de> References: <1348584961-1476-1-git-send-email-trenn@suse.de> Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org Signed-off-by: Thomas Renninger --- Documentation/acpi/initrd_table_override.txt | 94 ++++++++++++++++++++++++++ 1 files changed, 94 insertions(+), 0 deletions(-) create mode 100644 Documentation/acpi/initrd_table_override.txt diff --git a/Documentation/acpi/initrd_table_override.txt b/Documentation/acpi/initrd_table_override.txt new file mode 100644 index 0000000..35c3f54 --- /dev/null +++ b/Documentation/acpi/initrd_table_override.txt @@ -0,0 +1,94 @@ +Overriding ACPI tables via initrd +================================= + +1) Introduction (What is this about) +2) What is this for +3) How does it work +4) References (Where to retrieve userspace tools) + +1) What is this about +--------------------- + +If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible to +override nearly any ACPI table provided by the BIOS with an instrumented, +modified one. + +For a full list of ACPI tables that can be overridden, take a look at +the char *table_sigs[MAX_ACPI_SIGNATURE]; definition in drivers/acpi/osl.c +All ACPI tables iasl (Intel's ACPI compiler and disassembler) knows should +be overridable, except: + - ACPI_SIG_RSDP (has a signature of 6 bytes) + - ACPI_SIG_FACS (does not have an ordinary ACPI table header) +Both could get implemented as well. + + +2) What is this for +------------------- + +Please keep in mind that this is a debug option. +ACPI tables should not get overridden for productive use. +If BIOS ACPI tables are overridden the kernel will get tainted with the +TAINT_OVERRIDDEN_ACPI_TABLE flag. +Complain to your platform/BIOS vendor if you find a bug which is so sever +that a workaround is not accepted in the Linux kernel. + +Still, it can and should be enabled in any kernel, because: + - There is no functional change with not instrumented initrds + - It provides a powerful feature to easily debug and test ACPI BIOS table + compatibility with the Linux kernel. + + +3) How does it work +------------------- + +# Extract the machine's ACPI tables: +cd /tmp +acpidump >acpidump +acpixtract -a acpidump +# Disassemble, modify and recompile them: +iasl -d *.dat +# For example add this statement into a _PRT (PCI Routing Table) function +# of the DSDT: +Store("HELLO WORLD", debug) +iasl -sa dsdt.dsl +# Add the raw ACPI tables to an uncompressed cpio archive. +# They must be put into a /kernel/firmware/acpi directory inside the +# cpio archive. +# The uncompressed cpio archive must be the first. +# Other, typically compressed cpio archives, must be +# concatenated on top of the uncompressed one. +mkdir -p kernel/firmware/acpi +cp dsdt.aml kernel/firmware/acpi +# A maximum of: #define ACPI_OVERRIDE_TABLES 10 +# tables are currently allowed (see osl.c): +iasl -sa facp.dsl +iasl -sa ssdt1.dsl +cp facp.aml kernel/firmware/acpi +cp ssdt1.aml kernel/firmware/acpi +# Create the uncompressed cpio archive and concatenate the original initrd +# on top: +find kernel | cpio -H newc --create > /boot/instrumented_initrd +cat /boot/initrd >>/boot/instrumented_initrd +# reboot with increased acpi debug level, e.g. boot params: +acpi.debug_level=0x2 acpi.debug_layer=0xFFFFFFFF +# and check your syslog: +[ 1.268089] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0._PRT] +[ 1.272091] [ACPI Debug] String [0x0B] "HELLO WORLD" + +iasl is able to disassemble and recompile quite a lot different, +also static ACPI tables. + + +4) Where to retrieve userspace tools +------------------------------------ + +iasl and acpixtract are part of Intel's ACPICA project: +http://acpica.org/ +and should be packaged by distributions (for example in the acpica package +on SUSE). + +acpidump can be found in Len Browns pmtools: +ftp://kernel.org/pub/linux/kernel/people/lenb/acpi/utils/pmtools/acpidump +This tool is also part of the acpica package on SUSE. +Alternatively, used ACPI tables can be retrieved via sysfs in latest kernels: +/sys/firmware/acpi/tables