docs: power: convert docs to ReST and rename to *.rst

Convert the PM documents to ReST, in order to allow them to
build with Sphinx.

The conversion is actually:
  - add blank lines and indentation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>

1 files changed, 501 insertions, 0 deletions

diff --git a/Documentation/power/swsusp.rst b/Documentation/power/swsusp.rst
new file mode 100644
index 000000000000..d000312f6965
--- /dev/null
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+============
+Swap suspend
+============
+
+Some warnings, first.
+
+.. warning::
+
+   **BIG FAT WARNING**
+
+   If you touch anything on disk between suspend and resume...
+				...kiss your data goodbye.
+
+   If you do resume from initrd after your filesystems are mounted...
+				...bye bye root partition.
+
+			[this is actually same case as above]
+
+   If you have unsupported ( ) devices using DMA, you may have some
+   problems. If your disk driver does not support suspend... (IDE does),
+   it may cause some problems, too. If you change kernel command line
+   between suspend and resume, it may do something wrong. If you change
+   your hardware while system is suspended... well, it was not good idea;
+   but it will probably only crash.
+
+   ( ) suspend/resume support is needed to make it safe.
+
+   If you have any filesystems on USB devices mounted before software suspend,
+   they won't be accessible after resume and you may lose data, as though
+   you have unplugged the USB devices with mounted filesystems on them;
+   see the FAQ below for details.  (This is not true for more traditional
+   power states like "standby", which normally don't turn USB off.)
+
+Swap partition:
+  You need to append resume=/dev/your_swap_partition to kernel command
+  line or specify it using /sys/power/resume.
+
+Swap file:
+  If using a swapfile you can also specify a resume offset using
+  resume_offset=<number> on the kernel command line or specify it
+  in /sys/power/resume_offset.
+
+After preparing then you suspend by::
+
+	echo shutdown > /sys/power/disk; echo disk > /sys/power/state
+
+- If you feel ACPI works pretty well on your system, you might try::
+
+	echo platform > /sys/power/disk; echo disk > /sys/power/state
+
+- If you would like to write hibernation image to swap and then suspend
+  to RAM (provided your platform supports it), you can try::
+
+	echo suspend > /sys/power/disk; echo disk > /sys/power/state
+
+- If you have SATA disks, you'll need recent kernels with SATA suspend
+  support. For suspend and resume to work, make sure your disk drivers
+  are built into kernel -- not modules. [There's way to make
+  suspend/resume with modular disk drivers, see FAQ, but you probably
+  should not do that.]
+
+If you want to limit the suspend image size to N bytes, do::
+
+	echo N > /sys/power/image_size
+
+before suspend (it is limited to around 2/5 of available RAM by default).
+
+- The resume process checks for the presence of the resume device,
+  if found, it then checks the contents for the hibernation image signature.
+  If both are found, it resumes the hibernation image.
+
+- The resume process may be triggered in two ways:
+
+  1) During lateinit:  If resume=/dev/your_swap_partition is specified on
+     the kernel command line, lateinit runs the resume process.  If the
+     resume device has not been probed yet, the resume process fails and
+     bootup continues.
+  2) Manually from an initrd or initramfs:  May be run from
+     the init script by using the /sys/power/resume file.  It is vital
+     that this be done prior to remounting any filesystems (even as
+     read-only) otherwise data may be corrupted.
+
+Article about goals and implementation of Software Suspend for Linux
+====================================================================
+
+Author: Gábor Kuti
+Last revised: 2003-10-20 by Pavel Machek
+
+Idea and goals to achieve
+-------------------------
+
+Nowadays it is common in several laptops that they have a suspend button. It
+saves the state of the machine to a filesystem or to a partition and switches
+to standby mode. Later resuming the machine the saved state is loaded back to
+ram and the machine can continue its work. It has two real benefits. First we
+save ourselves the time machine goes down and later boots up, energy costs
+are real high when running from batteries. The other gain is that we don't have
+to interrupt our programs so processes that are calculating something for a long
+time shouldn't need to be written interruptible.
+
+swsusp saves the state of the machine into active swaps and then reboots or
+powerdowns.  You must explicitly specify the swap partition to resume from with
+`resume=` kernel option. If signature is found it loads and restores saved
+state. If the option `noresume` is specified as a boot parameter, it skips
+the resuming.  If the option `hibernate=nocompress` is specified as a boot
+parameter, it saves hibernation image without compression.
+
+In the meantime while the system is suspended you should not add/remove any
+of the hardware, write to the filesystems, etc.
+
+Sleep states summary
+====================
+
+There are three different interfaces you can use, /proc/acpi should
+work like this:
+
+In a really perfect world::
+
+  echo 1 > /proc/acpi/sleep       # for standby
+  echo 2 > /proc/acpi/sleep       # for suspend to ram
+  echo 3 > /proc/acpi/sleep       # for suspend to ram, but with more power conservative
+  echo 4 > /proc/acpi/sleep       # for suspend to disk
+  echo 5 > /proc/acpi/sleep       # for shutdown unfriendly the system
+
+and perhaps::
+
+  echo 4b > /proc/acpi/sleep      # for suspend to disk via s4bios
+
+Frequently Asked Questions
+==========================
+
+Q:
+  well, suspending a server is IMHO a really stupid thing,
+  but... (Diego Zuccato):
+
+A:
+  You bought new UPS for your server. How do you install it without
+  bringing machine down? Suspend to disk, rearrange power cables,
+  resume.
+
+  You have your server on UPS. Power died, and UPS is indicating 30
+  seconds to failure. What do you do? Suspend to disk.
+
+
+Q:
+  Maybe I'm missing something, but why don't the regular I/O paths work?
+
+A:
+  We do use the regular I/O paths. However we cannot restore the data
+  to its original location as we load it. That would create an
+  inconsistent kernel state which would certainly result in an oops.
+  Instead, we load the image into unused memory and then atomically copy
+  it back to it original location. This implies, of course, a maximum
+  image size of half the amount of memory.
+
+  There are two solutions to this:
+
+  * require half of memory to be free during suspend. That way you can
+    read "new" data onto free spots, then cli and copy
+
+  * assume we had special "polling" ide driver that only uses memory
+    between 0-640KB. That way, I'd have to make sure that 0-640KB is free
+    during suspending, but otherwise it would work...
+
+  suspend2 shares this fundamental limitation, but does not include user
+  data and disk caches into "used memory" by saving them in
+  advance. That means that the limitation goes away in practice.
+
+Q:
+  Does linux support ACPI S4?
+
+A:
+  Yes. That's what echo platform > /sys/power/disk does.
+
+Q:
+  What is 'suspend2'?
+
+A:
+  suspend2 is 'Software Suspend 2', a forked implementation of
+  suspend-to-disk which is available as separate patches for 2.4 and 2.6
+  kernels from swsusp.sourceforge.net. It includes support for SMP, 4GB
+  highmem and preemption. It also has a extensible architecture that
+  allows for arbitrary transformations on the image (compression,
+  encryption) and arbitrary backends for writing the image (eg to swap
+  or an NFS share[Work In Progress]). Questions regarding suspend2
+  should be sent to the mailing list available through the suspend2
+  website, and not to the Linux Kernel Mailing List. We are working
+  toward merging suspend2 into the mainline kernel.
+
+Q:
+  What is the freezing of tasks and why are we using it?
+
+A:
+  The freezing of tasks is a mechanism by which user space processes and some
+  kernel threads are controlled during hibernation or system-wide suspend (on some
+  architectures).  See freezing-of-tasks.txt for details.
+
+Q:
+  What is the difference between "platform" and "shutdown"?
+
+A:
+  shutdown:
+	save state in linux, then tell bios to powerdown
+
+  platform:
+	save state in linux, then tell bios to powerdown and blink
+        "suspended led"
+
+  "platform" is actually right thing to do where supported, but
+  "shutdown" is most reliable (except on ACPI systems).
+
+Q:
+  I do not understand why you have such strong objections to idea of
+  selective suspend.
+
+A:
+  Do selective suspend during runtime power management, that's okay. But
+  it's useless for suspend-to-disk. (And I do not see how you could use
+  it for suspend-to-ram, I hope you do not want that).
+
+  Lets see, so you suggest to
+
+  * SUSPEND all but swap device and parents
+  * Snapshot
+  * Write image to disk
+  * SUSPEND swap device and parents
+  * Powerdown
+
+  Oh no, that does not work, if swap device or its parents uses DMA,
+  you've corrupted data. You'd have to do
+
+  * SUSPEND all but swap device and parents
+  * FREEZE swap device and parents
+  * Snapshot
+  * UNFREEZE swap device and parents
+  * Write
+  * SUSPEND swap device and parents
+
+  Which means that you still need that FREEZE state, and you get more
+  complicated code. (And I have not yet introduce details like system
+  devices).
+
+Q:
+  There don't seem to be any generally useful behavioral
+  distinctions between SUSPEND and FREEZE.
+
+A:
+  Doing SUSPEND when you are asked to do FREEZE is always correct,
+  but it may be unnecessarily slow. If you want your driver to stay simple,
+  slowness may not matter to you. It can always be fixed later.
+
+  For devices like disk it does matter, you do not want to spindown for
+  FREEZE.
+
+Q:
+  After resuming, system is paging heavily, leading to very bad interactivity.
+
+A:
+  Try running::
+
+    cat /proc/[0-9]*/maps | grep / | sed 's:.* /:/:' | sort -u | while read file
+    do
+      test -f "$file" && cat "$file" > /dev/null
+    done
+
+  after resume. swapoff -a; swapon -a may also be useful.
+
+Q:
+  What happens to devices during swsusp? They seem to be resumed
+  during system suspend?
+
+A:
+  That's correct. We need to resume them if we want to write image to
+  disk. Whole sequence goes like
+
+      **Suspend part**
+
+      running system, user asks for suspend-to-disk
+
+      user processes are stopped
+
+      suspend(PMSG_FREEZE): devices are frozen so that they don't interfere
+      with state snapshot
+
+      state snapshot: copy of whole used memory is taken with interrupts disabled
+
+      resume(): devices are woken up so that we can write image to swap
+
+      write image to swap
+
+      suspend(PMSG_SUSPEND): suspend devices so that we can power off
+
+      turn the power off
+
+      **Resume part**
+
+      (is actually pretty similar)
+
+      running system, user asks for suspend-to-disk
+
+      user processes are stopped (in common case there are none,
+      but with resume-from-initrd, no one knows)
+
+      read image from disk
+
+      suspend(PMSG_FREEZE): devices are frozen so that they don't interfere
+      with image restoration
+
+      image restoration: rewrite memory with image
+
+      resume(): devices are woken up so that system can continue
+
+      thaw all user processes
+
+Q:
+  What is this 'Encrypt suspend image' for?
+
+A:
+  First of all: it is not a replacement for dm-crypt encrypted swap.
+  It cannot protect your computer while it is suspended. Instead it does
+  protect from leaking sensitive data after resume from suspend.
+
+  Think of the following: you suspend while an application is running
+  that keeps sensitive data in memory. The application itself prevents
+  the data from being swapped out. Suspend, however, must write these
+  data to swap to be able to resume later on. Without suspend encryption
+  your sensitive data are then stored in plaintext on disk.  This means
+  that after resume your sensitive data are accessible to all
+  applications having direct access to the swap device which was used
+  for suspend. If you don't need swap after resume these data can remain
+  on disk virtually forever. Thus it can happen that your system gets
+  broken in weeks later and sensitive data which you thought were
+  encrypted and protected are retrieved and stolen from the swap device.
+  To prevent this situation you should use 'Encrypt suspend image'.
+
+  During suspend a temporary key is created and this key is used to
+  encrypt the data written to disk. When, during resume, the data was
+  read back into memory the temporary key is destroyed which simply
+  means that all data written to disk during suspend are then
+  inaccessible so they can't be stolen later on.  The only thing that
+  you must then take care of is that you call 'mkswap' for the swap
+  partition used for suspend as early as possible during regular
+  boot. This asserts that any temporary key from an oopsed suspend or
+  from a failed or aborted resume is erased from the swap device.
+
+  As a rule of thumb use encrypted swap to protect your data while your
+  system is shut down or suspended. Additionally use the encrypted
+  suspend image to prevent sensitive data from being stolen after
+  resume.
+
+Q:
+  Can I suspend to a swap file?
+
+A:
+  Generally, yes, you can.  However, it requires you to use the "resume=" and
+  "resume_offset=" kernel command line parameters, so the resume from a swap file
+  cannot be initiated from an initrd or initramfs image.  See
+  swsusp-and-swap-files.txt for details.
+
+Q:
+  Is there a maximum system RAM size that is supported by swsusp?
+
+A:
+  It should work okay with highmem.
+
+Q:
+  Does swsusp (to disk) use only one swap partition or can it use
+  multiple swap partitions (aggregate them into one logical space)?
+
+A:
+  Only one swap partition, sorry.
+
+Q:
+  If my application(s) causes lots of memory & swap space to be used
+  (over half of the total system RAM), is it correct that it is likely
+  to be useless to try to suspend to disk while that app is running?
+
+A:
+  No, it should work okay, as long as your app does not mlock()
+  it. Just prepare big enough swap partition.
+
+Q:
+  What information is useful for debugging suspend-to-disk problems?
+
+A:
+  Well, last messages on the screen are always useful. If something
+  is broken, it is usually some kernel driver, therefore trying with as
+  little as possible modules loaded helps a lot. I also prefer people to
+  suspend from console, preferably without X running. Booting with
+  init=/bin/bash, then swapon and starting suspend sequence manually
+  usually does the trick. Then it is good idea to try with latest
+  vanilla kernel.
+
+Q:
+  How can distributions ship a swsusp-supporting kernel with modular
+  disk drivers (especially SATA)?
+
+A:
+  Well, it can be done, load the drivers, then do echo into
+  /sys/power/resume file from initrd. Be sure not to mount
+  anything, not even read-only mount, or you are going to lose your
+  data.
+
+Q:
+  How do I make suspend more verbose?
+
+A:
+  If you want to see any non-error kernel messages on the virtual
+  terminal the kernel switches to during suspend, you have to set the
+  kernel console loglevel to at least 4 (KERN_WARNING), for example by
+  doing::
+
+	# save the old loglevel
+	read LOGLEVEL DUMMY < /proc/sys/kernel/printk
+	# set the loglevel so we see the progress bar.
+	# if the level is higher than needed, we leave it alone.
+	if [ $LOGLEVEL -lt 5 ]; then
+	        echo 5 > /proc/sys/kernel/printk
+		fi
+
+        IMG_SZ=0
+        read IMG_SZ < /sys/power/image_size
+        echo -n disk > /sys/power/state
+        RET=$?
+        #
+        # the logic here is:
+        # if image_size > 0 (without kernel support, IMG_SZ will be zero),
+        # then try again with image_size set to zero.
+	if [ $RET -ne 0 -a $IMG_SZ -ne 0 ]; then # try again with minimal image size
+                echo 0 > /sys/power/image_size
+                echo -n disk > /sys/power/state
+                RET=$?
+        fi
+
+	# restore previous loglevel
+	echo $LOGLEVEL > /proc/sys/kernel/printk
+	exit $RET
+
+Q:
+  Is this true that if I have a mounted filesystem on a USB device and
+  I suspend to disk, I can lose data unless the filesystem has been mounted
+  with "sync"?
+
+A:
+  That's right ... if you disconnect that device, you may lose data.
+  In fact, even with "-o sync" you can lose data if your programs have
+  information in buffers they haven't written out to a disk you disconnect,
+  or if you disconnect before the device finished saving data you wrote.
+
+  Software suspend normally powers down USB controllers, which is equivalent
+  to disconnecting all USB devices attached to your system.
+
+  Your system might well support low-power modes for its USB controllers
+  while the system is asleep, maintaining the connection, using true sleep
+  modes like "suspend-to-RAM" or "standby".  (Don't write "disk" to the
+  /sys/power/state file; write "standby" or "mem".)  We've not seen any
+  hardware that can use these modes through software suspend, although in
+  theory some systems might support "platform" modes that won't break the
+  USB connections.
+
+  Remember that it's always a bad idea to unplug a disk drive containing a
+  mounted filesystem.  That's true even when your system is asleep!  The
+  safest thing is to unmount all filesystems on removable media (such USB,
+  Firewire, CompactFlash, MMC, external SATA, or even IDE hotplug bays)
+  before suspending; then remount them after resuming.
+
+  There is a work-around for this problem.  For more information, see
+  Documentation/driver-api/usb/persist.rst.
+
+Q:
+  Can I suspend-to-disk using a swap partition under LVM?
+
+A:
+  Yes and No.  You can suspend successfully, but the kernel will not be able
+  to resume on its own.  You need an initramfs that can recognize the resume
+  situation, activate the logical volume containing the swap volume (but not
+  touch any filesystems!), and eventually call::
+
+    echo -n "$major:$minor" > /sys/power/resume
+
+  where $major and $minor are the respective major and minor device numbers of
+  the swap volume.
+
+  uswsusp works with LVM, too.  See http://suspend.sourceforge.net/
+
+Q:
+  I upgraded the kernel from 2.6.15 to 2.6.16. Both kernels were
+  compiled with the similar configuration files. Anyway I found that
+  suspend to disk (and resume) is much slower on 2.6.16 compared to
+  2.6.15. Any idea for why that might happen or how can I speed it up?
+
+A:
+  This is because the size of the suspend image is now greater than
+  for 2.6.15 (by saving more data we can get more responsive system
+  after resume).
+
+  There's the /sys/power/image_size knob that controls the size of the
+  image.  If you set it to 0 (eg. by echo 0 > /sys/power/image_size as
+  root), the 2.6.15 behavior should be restored.  If it is still too
+  slow, take a look at suspend.sf.net -- userland suspend is faster and
+  supports LZF compression to speed it up further.