linux-kernel - Re: [PATCH] nokia n900: update dts with camera support

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Message-ID: <20170817000845.agkcuvqaheejm33j@earth>
Date:   Thu, 17 Aug 2017 02:08:45 +0200
From:   Sebastian Reichel <sre@...nel.org>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     Pavel Machek <pavel@....cz>, pali.rohar@...il.com,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-omap@...r.kernel.org, tony@...mide.com, khilman@...nel.org,
        aaro.koskinen@....fi, ivo.g.dimitrov.75@...il.com,
        patrikbachan@...il.com, serge@...lyn.com, abcloriens@...il.com
Subject: Re: [PATCH] nokia n900: update dts with camera support

Hi,

On Thu, Aug 17, 2017 at 12:23:44AM +0300, Sakari Ailus wrote:
> On Wed, Aug 16, 2017 at 10:59:15PM +0200, Pavel Machek wrote:
> > > On Wed, Aug 16, 2017 at 12:03:49AM +0200, Pavel Machek wrote:
> > > > diff --git a/Documentation/devicetree/bindings/media/video-interfaces.txt b/Documentation/devicetree/bindings/media/video-interfaces.txt
> > > > index 852041a..aade681 100644
> > > > --- a/Documentation/devicetree/bindings/media/video-interfaces.txt
> > > > +++ b/Documentation/devicetree/bindings/media/video-interfaces.txt
> > > > @@ -119,6 +119,8 @@ Optional endpoint properties
> > > >    as 0 (normal). This property is valid for serial busses only.
> > > >  - strobe: Whether the clock signal is used as clock (0) or strobe (1). Used
> > > >    with CCP2, for instance.
> > > > +- clock-inv: polarity of clock/strobe signal. 0 - not inverted, 1 - inverted
> > > > +- crc: crc is in use
> > > 
> > > booleans in DT are not done with <0> and <1>, but as properties without
> > > values. True = property exists, False = property does not exist.
> 
> Now that you mention it, I remember that now.
> 
> > Well, strobe property above already uses = <0>/<1> format, as do
> > others.
>
> > Problem with "false = property does not exist" is that you don't know
> > if it is "someone forgot to define it" or "someone made a typo" or
> > "dts is too old to know about this property" or "the property indeed
> > should be false"...
>
> As this is an established practice, I think we should follow it for bool
> properties.

Yes it's common practice, there is also device_property_read_bool()
to get the value.

> We could change the existing ones, too, and leave some extra checks in
> place to handle old dtbs.

The following should be downward compatible:

var = read_bool();
if (var && !read_int())
    var = false;

Btw. DT people should be CC'd for DT binding additions/changes.

-- Sebastian

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