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
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