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Re: [PATCH 5/6 #3] RTC: SMBus support for the M41T80, etc. driver

Subject: Re: [PATCH 5/6 #3] RTC: SMBus support for the M41T80, etc. driver
From: Atsushi Nemoto <>
Date: Tue, 20 May 2008 10:25:59 +0900 (JST)
In-reply-to: <>
Original-recipient: rfc822;
References: <>
On Sun, 18 May 2008 04:53:54 +0100 (BST), "Maciej W. Rozycki" 
<> wrote:
>  The BCM1250A SOC which is used on the SWARM board utilising an M41T81
> chip only supports pure I2C in the raw bit-banged mode.  Nobody sane
> really wants to use it unless absolutely necessary and the M41T80, etc.  
> chips work just fine with an SMBus adapter which is what the standard mode
> of operation of the BCM1250A.  The only drawback of byte accesses with the
> M41T80 is the chip only latches clock data registers for the duration of
> an I2C transaction which works fine with a block transfers, but not
> byte-wise accesses.
>  The driver currently requires an I2C adapter providing both SMBus and raw
> I2C access.  This is a set of changes to make it work with any SMBus
> adapter providing at least read byte and write byte protocols.  
> Additionally, if a given SMBus adapter supports I2C block read and/or
> write protocols (a common extension beyond the SMBus spec), they are used
> as well.  The problem of unlatched clock data if SMBus byte transactions
> are used is resolved in the standard way.  For raw I2C controllers this
> functionality is provided by the I2C core as SMBus emulation in a
> transparent way.
> Signed-off-by: Maciej W. Rozycki <>

Tested-by: Atsushi Nemoto <>

Atsushi Nemoto

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