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Date: Thu, 17 Apr 2008 14:46:40 +0200
From: Jochen Friedrich <jochen@scram.de>
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To: Laurent Pinchart <laurentp@cse-semaphore.com>
Subject: Re: [PATCH] powerpc: Implement GPIO LIB API on CPM2 Freescale SoC.
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Hi Laurent,

> BTW, what's the purpose of the shadow data register in the CPM GPIO chip 
> structure ? As the set operation is protected by a spinlock, the only use I 
> can think of is to prevent changing bits in the PDAT register for pins 
> configured as inputs. Is that correct ? If so this should be clearly 
> documented in the code.

It's for pins configured as open drain. See the discussion in:

http://ozlabs.org/pipermail/linuxppc-dev/2008-January/050826.html

Thanks,
Jochen