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Message-ID: <20190424162850.g5ripuixdkvvzsjm@mail.google.com>
Date: Thu, 25 Apr 2019 00:28:52 +0800
From: Changbin Du <changbin.du@...il.com>
To: Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
Cc: Changbin Du <changbin.du@...il.com>,
Jonathan Corbet <corbet@....net>,
Bjorn Helgaas <bhelgaas@...gle.com>, rjw@...ysocki.net,
linux-pci@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
x86@...nel.org, fenghua.yu@...el.com,
linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
linux-gpio@...r.kernel.org
Subject: Re: [PATCH v4 09/63] Documentation: ACPI: move
method-customizing.txt to firmware-guide/acpi and convert to reST
On Tue, Apr 23, 2019 at 06:03:16PM -0300, Mauro Carvalho Chehab wrote:
> Em Wed, 24 Apr 2019 00:28:38 +0800
> Changbin Du <changbin.du@...il.com> escreveu:
>
> > This converts the plain text documentation to reStructuredText format and
> > add it to Sphinx TOC tree. No essential content change.
> >
> > Signed-off-by: Changbin Du <changbin.du@...il.com>
> > ---
> > Documentation/acpi/method-customizing.txt | 73 -----------------
> > Documentation/firmware-guide/acpi/index.rst | 3 +-
> > .../acpi/method-customizing.rst | 82 +++++++++++++++++++
> > 3 files changed, 84 insertions(+), 74 deletions(-)
> > delete mode 100644 Documentation/acpi/method-customizing.txt
> > create mode 100644 Documentation/firmware-guide/acpi/method-customizing.rst
> >
> > diff --git a/Documentation/acpi/method-customizing.txt b/Documentation/acpi/method-customizing.txt
> > deleted file mode 100644
> > index 7235da975f23..000000000000
> > --- a/Documentation/acpi/method-customizing.txt
> > +++ /dev/null
> > @@ -1,73 +0,0 @@
> > -Linux ACPI Custom Control Method How To
> > -=======================================
> > -
> > -Written by Zhang Rui <rui.zhang@...el.com>
> > -
> > -
> > -Linux supports customizing ACPI control methods at runtime.
> > -
> > -Users can use this to
> > -1. override an existing method which may not work correctly,
> > - or just for debugging purposes.
> > -2. insert a completely new method in order to create a missing
> > - method such as _OFF, _ON, _STA, _INI, etc.
> > -For these cases, it is far simpler to dynamically install a single
> > -control method rather than override the entire DSDT, because kernel
> > -rebuild/reboot is not needed and test result can be got in minutes.
> > -
> > -Note: Only ACPI METHOD can be overridden, any other object types like
> > - "Device", "OperationRegion", are not recognized. Methods
> > - declared inside scope operators are also not supported.
> > -Note: The same ACPI control method can be overridden for many times,
> > - and it's always the latest one that used by Linux/kernel.
> > -Note: To get the ACPI debug object output (Store (AAAA, Debug)),
> > - please run "echo 1 > /sys/module/acpi/parameters/aml_debug_output".
> > -
> > -1. override an existing method
> > - a) get the ACPI table via ACPI sysfs I/F. e.g. to get the DSDT,
> > - just run "cat /sys/firmware/acpi/tables/DSDT > /tmp/dsdt.dat"
> > - b) disassemble the table by running "iasl -d dsdt.dat".
> > - c) rewrite the ASL code of the method and save it in a new file,
> > - d) package the new file (psr.asl) to an ACPI table format.
> > - Here is an example of a customized \_SB._AC._PSR method,
> > -
> > - DefinitionBlock ("", "SSDT", 1, "", "", 0x20080715)
> > - {
> > - Method (\_SB_.AC._PSR, 0, NotSerialized)
> > - {
> > - Store ("In AC _PSR", Debug)
> > - Return (ACON)
> > - }
> > - }
> > - Note that the full pathname of the method in ACPI namespace
> > - should be used.
> > - e) assemble the file to generate the AML code of the method.
> > - e.g. "iasl -vw 6084 psr.asl" (psr.aml is generated as a result)
> > - If parameter "-vw 6084" is not supported by your iASL compiler,
> > - please try a newer version.
> > - f) mount debugfs by "mount -t debugfs none /sys/kernel/debug"
> > - g) override the old method via the debugfs by running
> > - "cat /tmp/psr.aml > /sys/kernel/debug/acpi/custom_method"
> > -
> > -2. insert a new method
> > - This is easier than overriding an existing method.
> > - We just need to create the ASL code of the method we want to
> > - insert and then follow the step c) ~ g) in section 1.
> > -
> > -3. undo your changes
> > - The "undo" operation is not supported for a new inserted method
> > - right now, i.e. we can not remove a method currently.
> > - For an overridden method, in order to undo your changes, please
> > - save a copy of the method original ASL code in step c) section 1,
> > - and redo step c) ~ g) to override the method with the original one.
> > -
> > -
> > -Note: We can use a kernel with multiple custom ACPI method running,
> > - But each individual write to debugfs can implement a SINGLE
> > - method override. i.e. if we want to insert/override multiple
> > - ACPI methods, we need to redo step c) ~ g) for multiple times.
> > -
> > -Note: Be aware that root can mis-use this driver to modify arbitrary
> > - memory and gain additional rights, if root's privileges got
> > - restricted (for example if root is not allowed to load additional
> > - modules after boot).
> > diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
> > index 61d67763851b..d1d069b26bbc 100644
> > --- a/Documentation/firmware-guide/acpi/index.rst
> > +++ b/Documentation/firmware-guide/acpi/index.rst
> > @@ -10,5 +10,6 @@ ACPI Support
> > namespace
> > enumeration
> > osi
> > + method-customizing
> > DSD-properties-rules
> > - gpio-properties
> > + gpio-properties
> > \ No newline at end of file
> > diff --git a/Documentation/firmware-guide/acpi/method-customizing.rst b/Documentation/firmware-guide/acpi/method-customizing.rst
> > new file mode 100644
> > index 000000000000..32eb1cdc1549
> > --- /dev/null
> > +++ b/Documentation/firmware-guide/acpi/method-customizing.rst
> > @@ -0,0 +1,82 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +=======================================
> > +Linux ACPI Custom Control Method How To
> > +=======================================
> > +
> > +:Author: Zhang Rui <rui.zhang@...el.com>
> > +
> > +
> > +Linux supports customizing ACPI control methods at runtime.
> > +
> > +Users can use this to:
> > +
> > +1. override an existing method which may not work correctly,
> > + or just for debugging purposes.
> > +2. insert a completely new method in order to create a missing
> > + method such as _OFF, _ON, _STA, _INI, etc.
> > +
> > +For these cases, it is far simpler to dynamically install a single
> > +control method rather than override the entire DSDT, because kernel
> > +rebuild/reboot is not needed and test result can be got in minutes.
> > +
> > +.. note:: Only ACPI METHOD can be overridden, any other object types like
> > + "Device", "OperationRegion", are not recognized. Methods
> > + declared inside scope operators are also not supported.
> > +.. note:: The same ACPI control method can be overridden for many times,
> > + and it's always the latest one that used by Linux/kernel.
> > +.. note:: To get the ACPI debug object output (Store (AAAA, Debug)),
> > + please run "echo 1 > /sys/module/acpi/parameters/aml_debug_output".
>
> Hmm... this may work (not sure if Sphinx would warn or not), but it
> is visually bad on text mode. I would code it, instead, with something
> like:
>
> .. note::
>
> - Only ACPI METHOD can be overridden, any other object types like
> "Device", "OperationRegion", are not recognized. Methods
> declared inside scope operators are also not supported.
>
> - The same ACPI control method can be overridden for many times,
> and it's always the latest one that used by Linux/kernel.
>
> - To get the ACPI debug object output (Store (AAAA, Debug)),
> please run::
>
> echo 1 > /sys/module/acpi/parameters/aml_debug_output
>
> As this would make it visually better on both text and html formats.
>
No warnings given. Your suggested style is better so applied it. Thanks!
> > +
> > +1. override an existing method
> > +==============================
> > +a) get the ACPI table via ACPI sysfs I/F. e.g. to get the DSDT,
> > + just run "cat /sys/firmware/acpi/tables/DSDT > /tmp/dsdt.dat"
> > +b) disassemble the table by running "iasl -d dsdt.dat".
> > +c) rewrite the ASL code of the method and save it in a new file,
> > +d) package the new file (psr.asl) to an ACPI table format.
> > + Here is an example of a customized \_SB._AC._PSR method::
> > +
> > + DefinitionBlock ("", "SSDT", 1, "", "", 0x20080715)
> > + {
> > + Method (\_SB_.AC._PSR, 0, NotSerialized)
> > + {
> > + Store ("In AC _PSR", Debug)
> > + Return (ACON)
> > + }
> > + }
> > +
> > + Note that the full pathname of the method in ACPI namespace
> > + should be used.
> > +e) assemble the file to generate the AML code of the method.
> > + e.g. "iasl -vw 6084 psr.asl" (psr.aml is generated as a result)
> > + If parameter "-vw 6084" is not supported by your iASL compiler,
> > + please try a newer version.
>
> I would use ``iasl -vw 6084 psr.asl`` and ``-vw 6084``.
>
> > +f) mount debugfs by "mount -t debugfs none /sys/kernel/debug"
>
> I would do:
>
> f) mount debugfs by running::
>
> mount -t debugfs none /sys/kernel/debug
>
> As it makes a better html document. I believe that the focus here is
> sysadmins. Doing the above makes easier for them to cut and paste
> commands.
>
> > +g) override the old method via the debugfs by running
> > + "cat /tmp/psr.aml > /sys/kernel/debug/acpi/custom_method"
>
> Same applies here: I would also place the "cat" command on a literal
> block.
>
> > +
> > +2. insert a new method
> > +======================
> > +This is easier than overriding an existing method.
> > +We just need to create the ASL code of the method we want to
> > +insert and then follow the step c) ~ g) in section 1.
> > +
> > +3. undo your changes
> > +====================
> > +The "undo" operation is not supported for a new inserted method
> > +right now, i.e. we can not remove a method currently.
> > +For an overridden method, in order to undo your changes, please
> > +save a copy of the method original ASL code in step c) section 1,
> > +and redo step c) ~ g) to override the method with the original one.
> > +
> > +
> > +.. note:: We can use a kernel with multiple custom ACPI method running,
> > + But each individual write to debugfs can implement a SINGLE
> > + method override. i.e. if we want to insert/override multiple
> > + ACPI methods, we need to redo step c) ~ g) for multiple times.
> > +
> > +.. note:: Be aware that root can mis-use this driver to modify arbitrary
> > + memory and gain additional rights, if root's privileges got
> > + restricted (for example if root is not allowed to load additional
> > + modules after boot).
>
> Same comment as above: IMHO, having a single note block with the two
> notes would be better.
>
> Thanks,
> Mauro
--
Cheers,
Changbin Du
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