From b6ce4083ed8e2a01a3a59301eabe0fc1e68a8a84 Mon Sep 17 00:00:00 2001
From: Vladimir Lebedev <vladimir.p.lebedev@intel.com>
Date: Tue, 20 Feb 2007 15:48:06 +0300
Subject: [PATCH] ACPI: Cache battery status instead of re-evaluating AML

/proc exports _BST in a single file, and _BST is re-evaulated
whenever that file is read.

Sometimes user-space reads this file frequently, and on some
systems _BST takes a long time to evaluate due to a slow EC.

Further, when we move to sysfs, the values returned from _BST
will be in multiple files, and evaluating _BST for each
file read would make matters worse.

Here code is added to support caching the results of _BST.
A new module parameter "update_time" tells how many seconds the
cached _BST should be used before it is re-evaluated.
Currently, update_time defaults to 0, and so the
existing behaviour of re-evaluating on each read retained.

Signed-off-by: Vladimir Lebedev <vladimir.p.lebedev@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
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