Re: [RFC/PATCH 02/13] media: s5p-csis: Add device tree support

[Sylwester Nawrocki <sylvester.nawrocki@gmail.com>]

Hi Laurent,

On 07/26/2012 04:38 PM, Laurent Pinchart wrote:
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/video/mipi.txt
>>>> @@ -0,0 +1,5 @@
>>>> +Common properties of MIPI-CSI1 and MIPI-CSI2 receivers and transmitters
>>>> +
>>>> + - data-lanes : number of differential data lanes wired and actively
>>>> used in
>>>> +		communication between the transmitter and the receiver, this
>>>> +		excludes the clock lane;
>>>
>>> Wouldn't it be better to use the standard "bus-width" DT property?
>>
>> I can't see any problems with using "bus-width". It seems sufficient
>> and could indeed be better, without a need to invent new MIPI-CSI
>> specific names. That was my first RFC on that and my perspective
>> wasn't probably broad enough. :)
> 
> What about CSI receivers that can reroute the lanes internally ? We would need
> to specify lane indices for each lane then, maybe with something like
> 
> clock-lane =<0>;
> data-lanes =<2 3 1>;

Sounds good to me. And the clock-lane could be made optional, as not all
devices would need it.
 
However, as far as I can see, there is currently no generic API for handling 
this kind of data structure. E.g. number of cells for the "interrupts"
property is specified with an additional "#interrupt-cells" property.

It would have been much easier to handle something like:

data-lanes = <2>, <3>, <1>;

i.e. an array of the lane indexes.

> For receivers that can't reroute lanes internally, the data-lanes property
> would be need to specify lanes in sequence.
> 
> data-lanes =<1 2 3>;

In this case we would be only interested in the number of cells in this
property, but how it could be retrieved ? With an array, it could have been
calculated from property length returned by of_property_find() (divided by
sizof(u32)).

--

Regards,
Sylwester