Re: [PATCH 0/4] spi: dw: fixes, and manages resources migration

[Baruch Siach <baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org>]

Hi Gerhard,

On Tue, Dec 31, 2013 at 01:34:25PM +0100, Gerhard Sittig wrote:
> On Thu, Dec 26, 2013 at 22:34 +0200, Baruch Siach wrote:
> > That's what I meant. The "dummy-cs" should be an internal
> > chip-select that does not control any slave signal. [ ... ]
> 
> Ah, nevermind then, I simply misunderstood. :)

Thinking about it again I think that "dummy-cs" is not a good name. Maybe 
"disconnected-cs" would be better. This is the actual hardware level 
description of the chip-select, rather than software level use as dummy value.

[...]

> So the introduction of another dummy-cs property might be
> appropriate given the observed behaviour of the hardware.
> Alternatively one might just pick an arbitrary internal CS number
> at runtime (probably the highest internal number, i.e. the last
> one), which should not be a problem as long as this behaviour is
> documented -- GPIOs then can get used for this CS number and all
> numbers above, so no functionality is missing.  Mind that this
> workaround then is a feature of the Linux driver, and not the DT
> binding.

Choosing an arbitrary chip-select number is dangerous. You might damage the 
hardware by choosing wrong. I don't think that relying on documentation 
(where?) is reasonable in this case.

baruch

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