Message-Id: <1181579321.28514.304.camel@queen.suse.de>
Date:	Mon, 11 Jun 2007 18:28:41 +0200
From:	Thomas Renninger <trenn@...e.de>
To:	"Brown, Len" <len.brown@...el.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-acpi <linux-acpi@...r.kernel.org>,
	Jesper Juhl <jesper.juhl@...il.com>,
	Zhang Rui <rui.zhang@...el.com>,
	Alexey Starikovskiy <aystarik@...il.com>
Subject: Re: Documentation - How to debug ACPI Problems

Thanks a lot for all your input!

Here is an updated version in patch format.
Len, it would be great if you can also add this one to your test tree.

On Wed, 2007-06-06 at 16:59 +0200, Jesper Juhl wrote:
> On 06/06/07, Thomas Renninger <trenn@...e.de> wrote:
> > Hi,
> >
> > (patches already exist in
> >          2.6.22-rcX-mm?) to send syslog messages over firewire.
> >          The latter might be the only way to debug early hangs on laptops
> >          without serial console anyway.
> >
> 
> "without a serial console" ???
Without a serial device (or serial port?), better?
> 
> >    3.2.2 Using ACPI_DEBUG Boot Parameters via /sysfs and /proc
> >
> >          The same as 3.2.1., you can also pass the parameters at runtime e.g.
> >          via:
> >          echo 0x1F >/proc/acpi/debug_level    # before 2.6.22 or
> >          echo ?!?  >/sys/?/!/?                # Rui?
> 
> Seems like some bits are missing here ^^^
Thanks to Rui, updated..

    Thomas

Create Documentation/acpi dir and add first ACPI debug How-To

Signed-off-by: Thomas Renninger <trenn@...e.de>

---
 Documentation/00-INDEX                |    3 
 Documentation/acpi/00-INDEX           |    4 
 Documentation/acpi/acpi_debugging.txt |  181 ++++++++++++++++++++++++++++++++++
 3 files changed, 188 insertions(+)

Index: linux-2.6.22-rc3/Documentation/acpi/acpi_debugging.txt
===================================================================
--- /dev/null
+++ linux-2.6.22-rc3/Documentation/acpi/acpi_debugging.txt
@@ -0,0 +1,181 @@
+How to debug ACPI (Advanced Configuration and Power Interface) Problems
+=======================================================================
+
+Thomas Renninger <trenn@...e.de>, 2007
+Copyright (C) 2007 SUSE Linux GmbH
+
+
+1. Introduction
+---------------
+
+1.1. General Info
+- - - - - - - -
+
+Please refer to the latest ACPI spec for general ACPI information:
+http://www.acpi.info/spec.htm
+
+
+ACPI is required by most recent x86, x86_64 and IA64 architecture based
+machines.
+
+In general ACPI tables provide information from the BIOS to the OS.
+There are ACPI tables (DSDT and SSDTs), written in the ACPI Source
+Language (ASL) which include byte code (similar to Java byte code) that gets
+interpreted by the OS. The kernel makes use of BIOS functions declared and
+described there by interpreting them to setup and access different hardware.
+
+There exist two compilers/interpreters for ASL code, one from Microsoft and
+one from Intel. The Intel code has an Open Source license. The software package
+is called ACPICA. It includes the code for disassembling DSDT tables,
+(re-)compiling them, parsing several ACPI tables and interpreting ACPI Machine
+Language (AML, the compiled ASL..). The code is used to provide several
+userspace tools, but large parts are also contributed to the linux kernel and
+other OSs.
+drivers/acpi/*.c currently is Linux code implementing most parts of the ACPI
+spec, everything in the directories below, gets synchronized with the ACPICA
+Intel package.
+
+
+1.2. Useful Userspace Tools for Table Playing
+- - - - - - - - - - - - - - - - - - - - - - -
+
+The ACPI tables of your system can be extracted with the acpidump tool in the
+latest pmutils package from here:
+ftp://ftp.kernel.org/pub/linux/kernel/people/lenb/acpi/utils
+
+acpixtract, iasl, acpiexec can be found in the ACPICA sources:
+http://developer.intel.com/technology/iapc/acpi/downloads.htm
+
+You can now:
+acpidump >acpidump       # cp your ACPI tables from memory to disk
+acpixtract -a acpidump   # extract them into raw, single tables
+iasl -d TABLE.dat        # disassemble/parse a specific table
+iasl -sa DSDT.dsl        # e.g. recompile a modified, disassembled DSDT for
+                           initramfs inclusion (see later)
+acpiexec DSDT.dat        # parse, interpret and load a DSDT in userspace
+
+The latter can sometimes be very useful to debug buggy DSDTs in userspace.
+It provides a debug shell which e.g. offers execution of specific ACPI
+functions, increase of debug output and more.
+
+
+2. Overriding DSDT
+------------------
+
+The DSDT (there is a patch also for SSDTs) can be overridden by the user.
+The tables get copied to RAM when booting and the kernel can override them with
+alternative tables at early boot time.
+
+Historically people used to override their DSDT to workaround BIOS or even
+kernel bugs. This is a bad idea, the override functionality is for short
+term workarounds and mainly for debugging! Please always report such bugs to
+bugzilla.kernel.org or post to linux-acpi@...r.kernel.org if unsure.
+
+There are two possibilities to override the DSDT:
+
+  - via CONFIG_ACPI_CUSTOM_DSDT (and _FILE) compile option(s)
+  - via adding a customized DSDT into initramfs
+
+The second approach does not need kernel recompilation and some distributions
+provide the patch, which is not included in mainline, in their kernels.
+
+The patch and more information can be found here (many thanks to Markus
+Gaugusch and Eric Piel):
+http://gaugusch.at/kernel.shtml
+
+
+3. Problem Analysis and Solving
+-------------------------------
+
+3.1. I see Warnings or Errors when disassembling or compiling my DSDT
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+Some might be sever ACPICA or BIOS bugs, some might just be incompatibilities
+with the Microsoft compiler. We want to fix both, therefore a bug should be
+filed at bugzilla.kernel.org
+In general you should watch your system, if you don't miss any functionality
+there is no reason to panic (e.g. modify the DSDT and override your original
+one, you really should not do that if you do not see any big advantage and even
+then, better try to get a real fix or at least a kernel workaround like a
+boot or module parameter).
+
+You should be able to debug this with userspace tools (See:
+"1.2. Useful Userspace Tools for Table Playing")
+
+
+3.2. Hardware accessed by ACPI is not working correctly - Using ACPI_DEBUG
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+If you suspect the bug to be in a module in drivers/acpi/*.c code, you may be
+able to find or narrow down the culprit simply by adding printk()'s.
+
+For more complicated bugs you should make use of the ACPI_DEBUG=y facility.
+This allows you to fine grain enable specific output in the ACPI interpreter.
+
+
+   3.2.1 Using ACPI_DEBUG Boot Parameters acpi.debug_level and acpi.debug_layer
+
+         Note: In kernel versions before 2.6.22 the boot parameters were:
+	       acpi_dbg_level and acpi_dbg_layer
+
+         ACPI can produce tons of debug output if these debug masks are
+         switched to full on.
+	 include/acpi/acoutput.h shows which flags can be enabled for level and
+         layer (cat /proc/acpi/debug_{level,layer} also shows you the flags,
+	 but that interface will move to sysfs, not sure whether there still
+	 will be such a help).
+
+         Therefore, switch on debug flags carefully. You also might want to
+	 increase the kernel ring buffer by passing:
+	 log_buf_len=XY in bytes and later use dmesg -s XY to get more than
+	 16k kernel log output.
+	 Instead of serial console logging you might want to use the netconsole
+	 interface (Documentation/networking/netconsole.txt) to send syslog
+	 messages over network or firewire to send syslog messages over
+	 firewire.
+	 The latter might be the only way to debug early hangs on laptops
+	 without a serial device anyway.
+
+   3.2.2 Using ACPI_DEBUG Boot Parameters via /sysfs and /proc
+
+	 The same as 3.2.1., you can also pass the parameters at runtime e.g.
+	 via:
+	 echo 0x1F >/sys/module/acpi/parameters/debug_{level,layer}
+
+	 Be aware that this interface exists since 2.6.22. In older kernels
+	 it is /proc/acpi/debug_{level,layer}, which worked in the same way.
+
+	 Wrapping such statements around loading and unloading a bug affected
+	 ACPI module might give you the possibility to increase debug_level,
+	 but still only give you a manageable amount of debug output.
+
+   3.2.3 Using ACPI_DEBUG ASL debug object
+
+	 You can also add a kind of printk to DSDT code(see 2. Overriding DSDT)
+	 Store (XY, debug), will print the value of the ACPI XY variable into
+	 syslog. Be aware that you need to have the
+	 #define ACPI_LV_DEBUG_OBJECT        0x00000008
+	 value defined in the debug_level mask to see any output.
+	 This may only be useful if you get too much output with 3.2.[12] and
+	 you think it is convenient to debug a very specific part of the ACPI
+	 code.
+
+   3.2.4 Using ACPI_DEBUG acpi_dbg_layer and acpi_dbg_level kernel variables
+
+	 Similar, but more powerful than 3.2.3 is to modify the global kernel
+	 variables for level and layer conditionally in the kernel code for
+	 your needs.
+	 E.g.
+	 acpi_debug_level=0xFFFFFFFF /* increase debug output to max */
+	 status = acpi_ut_evaluate_object(...) /* by kernel invoked ACPI method
+						  that should get debugged with
+						  very high debug output*/
+ 	 acpi_debug_level=0x3        /* lower debug output again */
+
+
+
+
+"It seems unfortunate if we do this work and get our
+partners to do the work and the result is that Linux works great without
+having to do the work" (Bill Gates on Making ACPI Not Work with Linux,
+http://www.osnews.com/story.php/17689/Bill-Gates-on-Making-ACPI-Not-Work-with-Linux)
Index: linux-2.6.22-rc3/Documentation/acpi/00-INDEX
===================================================================
--- /dev/null
+++ linux-2.6.22-rc3/Documentation/acpi/00-INDEX
@@ -0,0 +1,4 @@
+00-INDEX
+	- this file
+acpi_debugging.txt
+	- How to debug ACPI problems
\ No newline at end of file
Index: linux-2.6.22-rc3/Documentation/00-INDEX
===================================================================
--- linux-2.6.22-rc3.orig/Documentation/00-INDEX
+++ linux-2.6.22-rc3/Documentation/00-INDEX
@@ -12,6 +12,9 @@ Following translations are available on 
 
 00-INDEX
 	- this file.
+acpi/
+	- general ACPI information
+
 BUG-HUNTING
 	- brute force method of doing binary search of patches to find bug.
 Changes


View attachment "acpi_debug_doc.patch" of type "text/x-patch" (9115 bytes)

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