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Documentation: Ask driver writers to provide PM support

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Add a paragraph in Documentation/SubmittingDrivers requesting that the
basic PM support be provided by new device drivers.

Add two new documents in Documentation/power/ giving general instructions
on debugging the suspend/resume functionality and testing the suspend and
resume support in device drivers.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: David Brownell <david-b@pacbell.net>
Cc: Nigel Cunningham <ncunningham@linuxmail.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rafael J. Wysocki 2007-05-08 00:24:07 -07:00 committed by Linus Torvalds
parent 8e2c20023f
commit 5b79520212
3 changed files with 163 additions and 0 deletions
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15
Documentation/SubmittingDrivers
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@ -87,6 +87,21 @@ Clarity: It helps if anyone can see how to fix the driver. It helps
driver that intentionally obfuscates how the hardware works
it will go in the bitbucket.
PM support: Since Linux is used on many portable and desktop systems, your
driver is likely to be used on such a system and therefore it
should support basic power management by implementing, if
necessary, the .suspend and .resume methods used during the
system-wide suspend and resume transitions. You should verify
that your driver correctly handles the suspend and resume, but
if you are unable to ensure that, please at least define the
.suspend method returning the -ENOSYS ("Function not
implemented") error. You should also try to make sure that your
driver uses as little power as possible when it's not doing
anything. For the driver testing instructions see
Documentation/power/drivers-testing.txt and for a relatively
complete overview of the power management issues related to
drivers see Documentation/power/devices.txt .
Control: In general if there is active maintainance of a driver by
the author then patches will be redirected to them unless
they are totally obvious and without need of checking.

106
Documentation/power/basic-pm-debugging.txt Normal file
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@ -0,0 +1,106 @@
Debugging suspend and resume
(C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL
1. Testing suspend to disk (STD)
To verify that the STD works, you can try to suspend in the "reboot" mode:
# echo reboot > /sys/power/disk
# echo disk > /sys/power/state
and the system should suspend, reboot, resume and get back to the command prompt
where you have started the transition. If that happens, the STD is most likely
to work correctly, but you need to repeat the test at least a couple of times in
a row for confidence. This is necessary, because some problems only show up on
a second attempt at suspending and resuming the system. You should also test
the "platform" and "shutdown" modes of suspend:
# echo platform > /sys/power/disk
# echo disk > /sys/power/state
or
# echo shutdown > /sys/power/disk
# echo disk > /sys/power/state
in which cases you will have to press the power button to make the system
resume. If that does not work, you will need to identify what goes wrong.
a) Test mode of STD
To verify if there are any drivers that cause problems you can run the STD
in the test mode:
# echo test > /sys/power/disk
# echo disk > /sys/power/state
in which case the system should freeze tasks, suspend devices, disable nonboot
CPUs (if any), wait for 5 seconds, enable nonboot CPUs, resume devices, thaw
tasks and return to your command prompt. If that fails, most likely there is
a driver that fails to either suspend or resume (in the latter case the system
may hang or be unstable after the test, so please take that into consideration).
To find this driver, you can carry out a binary search according to the rules:
- if the test fails, unload a half of the drivers currently loaded and repeat
(that would probably involve rebooting the system, so always note what drivers
have been loaded before the test),
- if the test succeeds, load a half of the drivers you have unloaded most
recently and repeat.
Once you have found the failing driver (there can be more than just one of
them), you have to unload it every time before the STD transition. In that case
please make sure to report the problem with the driver.
It is also possible that a cycle can still fail after you have unloaded
all modules. In that case, you would want to look in your kernel configuration
for the drivers that can be compiled as modules (testing again with them as
modules), and possibly also try boot time options such as "noapic" or "noacpi".
b) Testing minimal configuration
If the test mode of STD works, you can boot the system with "init=/bin/bash"
and attempt to suspend in the "reboot", "shutdown" and "platform" modes. If
that does not work, there probably is a problem with a driver statically
compiled into the kernel and you can try to compile more drivers as modules,
so that they can be tested individually. Otherwise, there is a problem with a
modular driver and you can find it by loading a half of the modules you normally
use and binary searching in accordance with the algorithm:
- if there are n modules loaded and the attempt to suspend and resume fails,
unload n/2 of the modules and try again (that would probably involve rebooting
the system),
- if there are n modules loaded and the attempt to suspend and resume succeeds,
load n/2 modules more and try again.
Again, if you find the offending module(s), it(they) must be unloaded every time
before the STD transition, and please report the problem with it(them).
c) Advanced debugging
In case the STD does not work on your system even in the minimal configuration
and compiling more drivers as modules is not practical or some modules cannot
be unloaded, you can use one of the more advanced debugging techniques to find
the problem. First, if there is a serial port in your box, you can set the
CONFIG_DISABLE_CONSOLE_SUSPEND kernel configuration option and try to log kernel
messages using the serial console. This may provide you with some information
about the reasons of the suspend (resume) failure. Alternatively, it may be
possible to use a FireWire port for debugging with firescope
(ftp://ftp.firstfloor.org/pub/ak/firescope/). On i386 it is also possible to
use the PM_TRACE mechanism documented in Documentation/s2ram.txt .
2. Testing suspend to RAM (STR)
To verify that the STR works, it is generally more convenient to use the s2ram
tool available from http://suspend.sf.net and documented at
http://en.opensuse.org/s2ram . However, before doing that it is recommended to
carry out the procedure described in section 1.
Assume you have resolved the problems with the STD and you have found some
failing drivers. These drivers are also likely to fail during the STR or
during the resume, so it is better to unload them every time before the STR
transition. Now, you can follow the instructions at
http://en.opensuse.org/s2ram to test the system, but if it does not work
"out of the box", you may need to boot it with "init=/bin/bash" and test
s2ram in the minimal configuration. In that case, you may be able to search
for failing drivers by following the procedure analogous to the one described in
1b). If you find some failing drivers, you will have to unload them every time
before the STR transition (ie. before you run s2ram), and please report the
problems with them.

42
Documentation/power/drivers-testing.txt Normal file
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@ -0,0 +1,42 @@
Testing suspend and resume support in device drivers
(C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL
1. Preparing the test system
Unfortunately, to effectively test the support for the system-wide suspend and
resume transitions in a driver, it is necessary to suspend and resume a fully
functional system with this driver loaded. Moreover, that should be done
several times, preferably several times in a row, and separately for the suspend
to disk (STD) and the suspend to RAM (STR) transitions, because each of these
cases involves different ordering of operations and different interactions with
the machine's BIOS.
Of course, for this purpose the test system has to be known to suspend and
resume without the driver being tested. Thus, if possible, you should first
resolve all suspend/resume-related problems in the test system before you start
testing the new driver. Please see Documents/power/basic-pm-debugging.txt for
more information about the debugging of suspend/resume functionality.
2. Testing the driver
Once you have resolved the suspend/resume-related problems with your test system
without the new driver, you are ready to test it:
a) Build the driver as a module, load it and try the STD in the test mode (see:
Documents/power/basic-pm-debugging.txt, 1a)).
b) Load the driver and attempt to suspend to disk in the "reboot", "shutdown"
and "platform" modes (see: Documents/power/basic-pm-debugging.txt, 1).
c) Compile the driver directly into the kernel and try the STD in the test mode.
d) Attempt to suspend to disk with the driver compiled directly into the kernel
in the "reboot", "shutdown" and "platform" modes.
e) Attempt to suspend to RAM using the s2ram tool with the driver loaded (see:
Documents/power/basic-pm-debugging.txt, 2). As far as the STR tests are
concerned, it should not matter whether or not the driver is built as a module.
Each of the above tests should be repeated several times and the STD tests
should be mixed with the STR tests. If any of them fails, the driver cannot be
regarded as suspend/resume-safe.