[PATCH] ARM: dts: vf610-zii-dev-rev-b: add hi8435 device

On Thu, 25 May 2017 11:03:20 +0300
Nikita Yushchenko [off-list ref] wrote:

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"Crap origin" here is that in vast majority of cases, polarity is
per-chip, not per-chip-use, knowledge. And proper location for per-chip
knowledge is chip's driver.  Moving this knowledge to per-chip-use
location in device trees only provides a source for errors, with little
gain.

Vladimir Barinov mentions possibility that signal can be inverted by
board between gpio provider and chip's pin ...   but do we have at least
one practical case of this?  And if we even do, it's quite uncommon, and
something special should be required in device tree for these special
cases and not for "normal" cases.  

I disagree.  Not for hi8435, but I have seen quite some board designs
invert GPIOs before getting them into board level components.  That's
why we should define those xxx-gpios properties on board level DTS,
where polarity can be chosen per board design.  

Even if such, still board specific knowledge is "is gpio as-is or
inverted", but knowledge if chip expects signal to be active low or
active high, remains chip-specific.

I'm thinking of proposing new flags in gpio binding, say
GPIO_NATIVE_POLARITY / GPIO_INVERTED_POLARITY,  that could be used
instead of GPIO_ACTIVE_HIGH / GPIO_ACTIVE_LOW, and leave knowledge about
signal polarity to chip's driver, while still allow to describe
inversion of needed.

Whilst I'm not certain on the precise approach (I'd be tempted by
heavy handed explicit representation of the inverting component) it
seems like this needs more thought.  I'm going to revert my
rather premature applying of the initial change for now.

Jonathan

Nikita