Re: adv7180 as SoC camera device

[Jonathan Cameron <jic23@cam.ac.uk>]

On 02/22/10 16:16, Guennadi Liakhovetski wrote:
> On Mon, 22 Feb 2010, Rodolfo Giometti wrote:
> 
>> On Fri, Feb 19, 2010 at 08:36:38PM +0100, Guennadi Liakhovetski wrote:
>>> On Fri, 19 Feb 2010, Rodolfo Giometti wrote:
>>>
>>>> Hello,
>>>>
>>>> on my pxa27x based board I have a adv7180 connected with the CIF
>>>> interface. Due this fact I'm going to use the pxa_camera.c driver
>>>> which in turn registers a soc_camera_host.
>>>>
>>>> In the latest kernel I found your driver for the ADV7180, but it
>>>> registers the chip as a v4l sub device.
>>>>
>>>> I suppose these two interfaces are not compatible, aren't they?
>>>
>>> Congratulations! Thereby you're in a position to develop the first 
>>> v4l2-subdev / soc-camera universal driver;) The answer to this your 
>>> question is - they are... kinda. This means - yes, soc-camera is also 
>>> using the v4l2-subdev API, but - with a couple of additions. Basically, 
>>> there are two things you have to change in the adv7180 driver to make it 
>>> compatible with soc-camera - (1) add bus-configuration methods, even if 
>>> they don't do much (see .query_bus_param() and .set_bus_param() methods 
>>> from struct soc_camera_ops), and (2) migrate the driver to the mediabus 
>>> API. The latter one requires some care - in principle, mediabus should be 
>>> the future API to negotiate parameters on the video bus between bridges 
>>> (in your case PXA CIF) and clients, but for you this means you also have 
>>> to migrate any other bridge drivers in the mainline to that API, and, if 
>>> they also interface to some other subdevices - those too, and if those can 
>>> also work with other bridges - those too...;) But, I think, that chain 
>>> will terminate quite soon, in fact, I cannot find any users of that driver 
>>> currently in the mainline, Richard?
>>>
>>>> In this situation, should I write a new driver for the
>>>> soc_camera_device? Which is The-Right-Thing(TM) to do? :)
>>>
>>> Please, have a look and try to convert the driver as described above. All 
>>> the APIs and a few examples are in the mainline, so, you should have 
>>> enough copy-paste sources;) Ask on the list (with me on cc) if anything is 
>>> still unclear.
>>
>> Thanks for your quick answer! :)
>>
>> What I still don't understand is if should I move the driver form
>> v4l2-subdev to a soc_camera device or trying to support both API...
> 
> Both. It is just one (v4l2-subdev) API, but soc-camera is using some 
> extensions to it.
> 
>> It seems to me that the driver is not used by any machines into
>> mainline
> 
> That makes your task even easier - you do not have to convert any bridge 
> drivers to mediabus API.
Indeed.  Having time to do that is what is delaying the ov7670 conversion.
(that and having time in general!)  For info I did post some untested
patches for the ov7670 a while back that show the minimal changes I think
are needed under these circumstances.

> 
>> so if soc-camera is also using the v4l2-subdev API but with a
>> couple of additions I suppose I can move it to soc_camera API...
> 
> Not move, extend. But preserve an ability to function without soc-camera 
> additions too. I.e., the use of soc-camera extensions should be optional 
> in your driver. Look here 
> http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/11486/focus=11493 
> for an example.
> 
> Thanks
> Guennadi
> ---
> Guennadi Liakhovetski, Ph.D.
> Freelance Open-Source Software Developer
> http://www.open-technology.de/
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