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

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Date:   Thu, 25 May 2017 11:03:20 +0300
From:   Nikita Yushchenko <nikita.yoush@...entembedded.com>
To:     Shawn Guo <shawnguo@...nel.org>
Cc:     Andrew Lunn <andrew@...n.ch>, Stefan Agner <stefan@...er.ch>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, Jeff White <Jeff.White@....aero>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Vladimir Barinov <vladimir.barinov@...entembedded.com>,
        linux-arm-kernel@...ts.infradead.org,
        Chris Healy <Chris.Healy@....aero>
Subject: Re: [PATCH] ARM: dts: vf610-zii-dev-rev-b: add hi8435 device

>> "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.

Nikita