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

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Date:   Thu, 25 May 2017 15:19:42 +0800
From:   Shawn Guo <shawnguo@...nel.org>
To:     Nikita Yushchenko <nikita.yoush@...entembedded.com>
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

On Tue, May 23, 2017 at 09:02:27AM +0300, Nikita Yushchenko wrote:
> >> However, hi8435 driver historically was coded using inverted values
> >> passed to gpiolib calls.  And there are setups in the wild with device
> >> trees containing GPIO_ACTIVE_HIGH that I'd prefer not breaking.
> >>
> >> To solve, I submitted a patch on hi8435 driver that changes to _raw()
> >> gpio calls (thus making it independent of what is written in device
> >> tree), and want [future] device trees not to contain explicitly written
> >> gpio polarity.
> > 
> > So maybe add another #define, GPIO_ACTIVE_IGNORED, to make it clear
> > that it does not matter what value you put there, it is ignored.
> 
> "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.

Shawn