Re: [PATCH 2.6-git] SPI: add set_clock() to bitbang

[Vitaly Wool <vwool@ru.mvista.com>]

David Brownell wrote:

>>>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.
>>    
>>
>
>Not a chance.  The clock is activated to talk to a given device;
>and there's no requirement that all devices on the bus use the
>same clock rate.  (If one chipselect gives access to a linked series
>of devices, clearly they'll all need to be clocked alike.  But
>that's not a bus, it's just a compound device ... like a big shift
>register.)
>
>I did my homework when putting that API together, and looked at
>quite a few SPI controllers.  **Not one** of them forces all
>their chipselets to use the same clock rate.
>  
>
I admit that thw word 'usually' is incorrect here, but still we have two 
Philips ARM boards where the SPI clock is configured _only_ on the bus, 
by setting the bus clock divisor on per-message basis. I was also 
keeping in mind PXA, so it wasn't just bare words...

Vitaly