Date:	Sat, 26 Jul 2008 08:29:11 +0200
From:	Elias Oltmanns <eo@...ensachen.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>, Jeff Garzik <jeff@...zik.org>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	Pavel Machek <pavel@....cz>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 5/5] Add documentation for hard disk shock protection
	interface

Put some information (and pointers to more) into the kernel's doc tree,
describing briefly how to set up disk shock protection under GNU/Linux.

Signed-off-by: Elias Oltmanns <eo@...ensachen.de>
---

 Documentation/laptops/disk-shock-protection.txt |   66 +++++++++++++++++++++++
 1 files changed, 66 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/laptops/disk-shock-protection.txt

diff --git a/Documentation/laptops/disk-shock-protection.txt b/Documentation/laptops/disk-shock-protection.txt
new file mode 100644
index 0000000..ac26040
--- /dev/null
+++ b/Documentation/laptops/disk-shock-protection.txt
@@ -0,0 +1,66 @@
+Hard disk shock protection
+==========================
+
+Author: Elias Oltmanns <eo@...ensachen.de>
+Last modified: 2008-07-24
+
+
+Intro
+-----
+
+ATA/ATAPI-7 specifies the IDLE IMMEDIATE command with UNLOAD FEATURE.
+Issuing this command should cause the drive to switch to idle mode and
+unload disk heads. This feature is being used in modern laptops in
+conjunction with accelerometers and appropriate software to implement
+a shock protection facility. The idea is to stop all I/O operations on
+the internal hard drive and park its heads on the ramp when critical
+situations are anticipated. The desire to have such a feature
+available on GNU/Linux systems has been the original motivation to
+implement a generic disk head parking interface in the Linux kernel.
+
+
+The interface
+-------------
+
+The interface works as follows: Writing an integer value to
+/sys/block/*/device/unload_heads will take the heads of the respective
+drive off the platter and block all I/O operations for the specified
+number of seconds. When the timeout expires and no further disk head
+park request has been issued in the meantime, normal operation will be
+resumed.
+
+FIXME:
+Once we've addressed the problem with pre-ATA-7 drives supporting the
+UNLOAD FEATURE but not announcing it properly, we'll document it
+accordingly.
+
+
+References
+----------
+
+There are several laptops from different brands featuring shock
+protection capabilities. As manufacturers have refused to support open
+source development of the required software components so far, Linux
+support for shock protection varies considerably between different
+hardware implementations. Ideally, this section should contain a list
+of pointers at different projects aiming at an implementation of shock
+protection on different systeems. Unfortunately, I only know of a
+single project which, although still considered experimental, is fit
+for use. Please feel free to add projects that have been the victims
+of my ignorance.
+
+- http://www.thinkwiki.org/wiki/HDAPS
+  See this page for information about Linux support of the hard disk
+  active protection syystem as implemented in IBM/Lenovo Thinkpads.
+  (FIXME: The information there will have to be updated once this
+  patch has been approved or the user interface has been agreed upon
+  at least.)
+
+
+CREDITS
+-------
+
+This implementation of disk head parking has been based on a patch
+originally published by Jon Escombe <lists@...sco.co.uk>. Assisted by
+various kernel developers, the author of this document has rewritten
+the original patch in order to make it fit for upstream submission.


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