Subject: Re: Documentation - How to debug ACPI Problems
From: Thomas Renninger <trenn@suse.de>
Reply-To: trenn@suse.de
To: Len Brown <lenb@kernel.org>
Cc: "Brown, Len" <len.brown@intel.com>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       linux-acpi <linux-acpi@vger.kernel.org>,
       Jesper Juhl <jesper.juhl@gmail.com>, Zhang Rui <rui.zhang@intel.com>,
       Alexey Starikovskiy <aystarik@gmail.com>
In-Reply-To: <200706180012.05665.lenb@kernel.org>
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Organization: Novell/SUSE
Date: Mon, 18 Jun 2007 13:18:47 +0200
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On Mon, 2007-06-18 at 00:12 -0400, Len Brown wrote:
> > +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@vger.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
> > +
> 
> how to override the DSDT by re-compiling the upstream kernel
> is already documented here:
> 
> http://ftp.kernel.org/pub/linux/kernel/people/lenb/acpi/patches/README.ACPI
Ah yes, a link to this one is quite convenient...

> It seems inconsistent to refer to the initrd patch from the in-tree Documentation,
> since that patch will always be out-of-tree.
It is inconsistent to point to a useful debug patch outside the kernel?

> I would think that the in-tree Documentation would refer to specifics relating
> to the kernel that is actually checked into the tree with the Documentation.
> This assumption can probably clear up some of the wording relating to the
> debug flags -- we don't have to describe the old ones -- if somebody is
> reading this documentation, they already have the new ones:-)
rip out mentioning /proc/acpi/debug_{level,layer}?
Ok.

> Asside from those specific things that describe the kernel in the tree,
> I'm thinking that acpi.sourceforge.net documentation would be a better
> place for a general HOWTO on debugging ACPI issues in general.
Looking at:
http://ftp.kernel.org/pub/linux/kernel/people/lenb/acpi/patches/README.ACPI,
maybe we could just add that one instead to Documentation/acpi/*?
If, splitting would IMO be easier to read, e.g. something like:
  - report_acpi_kernel_bugs.txt
  - sending_ACPI_patches.txt
  - debugging_acpi_kernel_errors.txt

      Thomas

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