Message-ID: <43ABA27C.6020309@ru.mvista.com>
Date: Fri, 23 Dec 2005 10:08:44 +0300
From: Vitaly Wool <vwool@ru.mvista.com>
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To: David Brownell <david-b@pacbell.net>
CC: linux-kernel@vger.kernel.org, spi-devel-general@sourceforge.net
Subject: Re: [PATCH 2.6-git] SPI: add set_clock() to bitbang
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David Brownell wrote:

>>No, suppose there're two devices behind the same SPI bus that have 
>>different clock constraints. As active SPI device change may well happen 
>>when each new message is processed, we'll need to set up clocks again 
>>for each message. Right?
>>    
>>
>
>Clock is coupled to chipselect/device.  When the bus controller
>switches to the other device, it updates the clock accordingly.
>  
>
Yeah, but chipselect is called on per-transfer basis what is likely to 
be redundant for clock setting.
Per-message clock configuration is enough AFAIS.

>How exactly that's done is system-specific.  Many controllers
>just have a register per chipselect, listing stuff like SPI mode,
>clock divisor, and word size.  So switching to that chipselect
>kicks those in automatically ... devices ignore the clock unless
>they've been selected.
>  
>
Hmm, usually clocks are configured for the bus not device.
So, summarizing, you haven't convinced me yet. :)

Vitaly
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