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From: Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: [Openipmi-developer] [patch 1/1] ipmi: add autosensing of ipmi
	device on powerpc using device-tree
Date: Sat, 9 Dec 2006 10:46:46 +0100
To: Arnd Bergmann <arnd@arndb.de>
Cc: linuxppc-dev@ozlabs.org, openipmi-developer@lists.sourceforge.net,
	Christian Krafft <krafft@de.ibm.com>
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>> How many registers do we expect here ? Might be better to have one
>> resource represent the whole MMIO area, and have a separate property
>> that indicates the stride between 2 registers.

Yes *please*.  Anything else will cause no end of problems, and
that only for wanting to not create a perfectly reasonable extra
property, with obvious semantics.

> I think the current representation is perfect. AFAICS, there are  
> always
> two registers,

How do you know?  Some later compatible implementation might add
some regs.  Also, there are implementations that simply ignore
the lower address bits, so size=1 in the "reg" property is wrong
for those.

> but depending on the HW implementation, they may be
> between 1 and 4 bytes wide, and can have a different spacing.

Always one byte wide.

> By having two separate areas in the reg property, the driver can
> easily determine both the size and the spacing. It will then do
> a single ioremap that spans both anyway.

It's much better to make it explicit and obvious in the device
tree what's going on.


Segher