[PATCH 5/6] mx31moboard: camera support

[Valentin Longchamp]

Guennadi Liakhovetski wrote:
> On Wed, 21 Oct 2009, Valentin Longchamp wrote:
> 
>> Sascha Hauer wrote:
>>> On Mon, Oct 19, 2009 at 06:41:13PM +0200, Valentin Longchamp wrote:
>>>> Hi Guennadi,
>>>>
>>>> Guennadi Liakhovetski wrote:
>>>>> Hi
>>>>>
>>>>> On Thu, 15 Oct 2009, Valentin Longchamp wrote:
>>>>>
>>>>>> We have two mt9t031 cameras that have a muxed bus on the robot.
>>>>>> We can control which one we are using with gpio outputs. This
>>>>>> currently is not optimal
>>>>> So, what prevents you from registering two platform devices for your two
>>>>> cameras? Is there a problem with that?
>>>> The lack of time until now to do it properly. I sent those patches as
>>>> initial RFC (and by the way thanks for your comment).
>>>>
>>>> I would like to have one video interface only and that I can switch
>>>> between the two physical camera using a quite simple system call. Would
>>>> that be compatible with registering the two platform devices ?
>>> Wouldn't it be better to have /dev/video[01] for two cameras? How do
>>> keep the registers synchron between both cameras otherwise?
>>>
>> Well, from my experimentations, most initializations are done when you open
>> the device. So if you close the device, switch camera and open it again, the
>> registers are initialized with the need values. Of course there is a problem
>> is you switch camera while the device is open.
>>
>> It could be ok with /dev/video[01], but I would need something that would
>> prevent one device to be opened when the other already is open (a mutex, but
>> where ?).
>>
>> Besides, I have read a slide from Dongsoo Kim
>> (http://www.celinuxforum.org/CelfPubWiki/ELC2009Presentations?action=AttachFile&do=get&target=Framework_for_digital_camera_in_linux-in_detail.ppt
>> slides 41-47) and the cleanest solution would be to have the two chips
>> enumerated with VIDIOC_ENUMINPUT as proposed. What would then be the v4l2 call
>> to switch from one device to each other ? How to "link" it with the kernel
>> code that make the real hardware switching ?
> 
> Ok, I don't have a definite answer to this, so, just my thoughts:
> 
> 1. soc-camera currently registers one struct v4l2_device device per _host_ 
> immediately upon its registration, and one struct video_device per 
> _client_ platform device.

Ok understood.

> 
> 2. we currently have 1 or 2 boards in the mainline with two video client 
> devices on one interface: arch/sh/boards/mach-migor/ and (unsure about) 
> arch/sh/boards/board-ap325rxa.c. At least the first of them exports two 
> platform devices and thus gets /dev/video[01]. Accesses are synchronised 
> with a mutex (I don't actually like that, I'd prefer to get a -EBUSY back 
> instead of hanging in D in open()), and a successful acquisition of the 
> mutex switches the respective camera on. See code for details. So, this 
> approach is supported and it works. In this case we have one v4l2_device 
> and two video_device instances, don't know whether this matches how this 
> is supposed to be done, but it works so far:-)

I am going to stick to this approach since it works now. This would 
allow me to have code that could go now into mainline.

> 
> 3. to support switching inputs, significant modifications to soc_camera.c 
> would be required. I read Nate's argument before, that as long as clients 
> can only be accessed one at a time, this should be presented by multiple 
> inputs rather than multiple device nodes. Somebody else from the V4L folk 
> has also confirmed this opinion. In principle I don't feel strongly either 
> way. But currently soc-camera uses a one i2c client to one device node 
> model, and I'm somewhat reluctant to change this before we're done with 
> the v4l2-subdev conversion.
> 

Sure, one step at a time. So for now the switching is not possible with 
soc_camera.

My problem is that both cameras have the same I2C address since they are 
the same.

Would I need to declare 2 i2c_device with the same address (I'm not sure 
it would even work ...) used by two _client_ platform_devices or would I 
have to have the two platform devices pointing to the same i2c_device ?

Thanks

Val

-- 
Valentin Longchamp, PhD Student, EPFL-STI-LSRO1
valentin.longchamp at epfl.ch, Phone: +41216937827
http://people.epfl.ch/valentin.longchamp
MEA3485, Station 9, CH-1015 Lausanne