linux-kernel - Re: [PATCH 3/4] spi: Add OF binding support for SPI busses

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Message-ID: <fa686aa40805211233h72a258bpf8c945b9f662d6ee@mail.gmail.com>
Date:	Wed, 21 May 2008 13:33:31 -0600
From:	"Grant Likely" <grant.likely@...retlab.ca>
To:	"Segher Boessenkool" <segher@...nel.crashing.org>
Cc:	"Guennadi Liakhovetski" <g.liakhovetski@....de>,
	linux-kernel@...r.kernel.org,
	spi-devel-general@...ts.sourceforge.net,
	dbrownell@...rs.sourceforge.net, linuxppc-dev@...abs.org,
	fabrizio.garetto@...il.com
Subject: Re: [PATCH 3/4] spi: Add OF binding support for SPI busses

On Wed, May 21, 2008 at 1:11 PM, Segher Boessenkool
<segher@...nel.crashing.org> wrote:
>> Ok, elegance apart:-) You can use the SPI-bridge construct to also
>> describe simple SPI-chipselect configurations. But is it really a good
>> idea? Wouldn't it be better to handle these two cases separately?
>
> It would be best to handle all these things that are specific to
> a certain SPI controller (like how CSs work) in the binding for
> that SPI controller, and not try to shoehorn all of this into some
> artificial generic framework.
>
> If you can have identical addresses on the SPI bus going to different
> devices based on which CS is asserted, you'll have to make the CS part
> of the "reg".  Example:
>
> spi-controller {
>        #address-cells = 2;
>        #size-cells = 0;
>        some-device@0,f000 { reg = < 0 f000 >; } // CS 0, SPI address f000
>        some-device@1,f000 { reg = < 1 f000 >; } // CS 1, SPI address f000
>        some-device@1,ff00 { reg = < 1 ff00 >; } // CS 1, SPI address ff00
> }

For SPI the CS # *is* the address.  :-)

Unlike I2C, SPI doesn't impose any protocol on the data.  It is all
anonymous data out, anonymous data in, a clock and a chip select.

Cheers,
g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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