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

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Message-ID: <2e7561f4-a160-9009-baa6-e056aa8f3887@iki.fi>
Date:   Thu, 17 Aug 2017 09:20:40 +0300
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Sebastian Reichel <sre@...nel.org>
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

Sebastian Reichel wrote:
> 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.

Pavel: could you also add linux-media as well for the next version, please?

-- 
Sakari Ailus
sakari.ailus@....fi