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

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Message-ID: <c97709fe-0c30-9f40-b4fe-740ad54bc5a7@gmail.com>
Date:   Mon, 28 Aug 2017 21:20:14 +0300
From:   Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
To:     Sakari Ailus <sakari.ailus@....fi>, Pavel Machek <pavel@....cz>
Cc:     Sebastian Reichel <sre@...nel.org>, 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, patrikbachan@...il.com, serge@...lyn.com,
        abcloriens@...il.com
Subject: Re: [PATCH] nokia n900: update dts with camera support

Hi

On 28.08.2017 18:07, Sakari Ailus wrote:
> Hi Pavel,
> 
> On Mon, Aug 28, 2017 at 03:59:59PM +0200, Pavel Machek wrote:
>> Hi!
>>
>>>>> 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.
>>
>> Ok, so for now we do crc=1 by default. Now we'd like to have crc
>> support configurable in the dts. But if we just introduce "crc;"
>> option, it will break old dts users. We could introduce "no-crc;" and
>> that would work in this particular case, but will break when we want
>> different defaults at different devices.
>>
>> Anyway, introducing "no-crc;" seems pretty ugly to me. I'd rather do
>> "crc=<0>;", in a similar way we handle other options now.
> 
> The same issue actually exists for CSI-2: the CRC is typically enabled and
> I think you can at least disable the check (in OMAP3 ISP). Do we have a
> need to disable it at the moment for any purpose? I think I've seen this
> was disabled somewhere but it may just as well be a thoughtlessly written
> configuration.
> 

Front camera has crc disabled in Nokia kernel. I am not sure the sensor 
supports crc at all.

Regards,
Ivo