Re: [PATCH 5/6] dt-bindings: iio: adc: mcp320x: Update for mcp3550/1/3

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On Sun, Sep 03, 2017 at 02:37:49PM +0100, Jonathan Cameron wrote:

> +cc Mark Brown and linux-spi to address question about how to represent
> a hardwired chip select.  See below for why I think that is what we should
> be representing rather than the fact it puts it in 'continuous mode'.

There's a good chance that if you just send me mail with a not obviously
related subject line it might get discarded unread, people CC me on lots
of things that are of questionable relevance.

> > >> > +   - microchip,continuous-conversion (boolean):
> > >> > +                   Only applicable to MCP3550/1/3:  These ADCs have long
> > >> > +                   conversion times and therefore support "continuous
> > >> > +                   conversion mode" to allow retrieval of conversions
> > >> > +                   at any time without observing a delay.  The mode is
> > >> > +                   enabled by permanently driving CS low, e.g. by wiring
> > >> > +                   it to ground.  

> hmm.  This is odd.  We probably need to make the SPI subsystem aware of this.
> It is possible to ask for exclusive use of an SPI bus and I think we should
> be doing this here.  It may be wired low on your board, but it may be wired to

This sounds like SPI_NO_CS, though it's vanishingly rare for it to be
implemented as there's a lot of ways for it to go wrong electrically -
it's a lot simpler to just have a chip select and minimise the number of
times it gets asserted.

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