linux-kernel - Add 1-wire (w1) support for DS2408 and multi-slave search in ds1wm

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Date:	Fri, 11 Mar 2011 16:38:30 -0500
From:	"Jean-François Dagenais" <jeff.dagenais@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	johnpol@....mipt.ru
Subject: Add 1-wire (w1) support for DS2408 and multi-slave search in ds1wm

The first patch add generic functionnality to w1_io for Resume Command [A5h]
lots of slaves support. I found it useful for multi-commands/reset workflows
with the same slave on a multi-slave bus.

This DS2408 w1 slave driver is not complete for all the 
features of the chip, but its sufficient if you use it as
a simple IO expander. Enjoy!

The ds1wm had Kconfig dependencies towards ARM && HAVE_CLK. I took them
out since I was using the ds1wm on an x86_64 platform (ds1wm in a FPGA through
pcie) and found them irrelevant.

The clock freq/divisors at the top of ds1wm.c did not have the MSB set to 1.
This bit is CLK_EN which turns the whole prescaler and dividers on. The driver
never mentionned this bit either, so I just included this bit right in the table
entries. I also took the liberty to add a couple of entries to the table. The
spec doesn't explicitely mentions these possibilities but the description and 
examination of the core shows the prescalers & dividers can be used for more
than the table explicitely shows. The table I enlarged still doesn't cover all
possibilities, but it's a good start.

I also made a few tweaks to a couple of the read and write algorithms which 
made sense while I had my head very deep in the ds1wm documentation. We stressed
it a lot with 10+ slaves on the bus, many ds2408, ds2431 and ds2433 at the same
time doing extensive interaction. It proved quite stable in our production 
environment.
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