Re: A question about DT support for soc_camera

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Hi Bryan,

On Wed, 15 Jan 2014, Bryan Wu wrote:

> Hi Guennadi,
> 
> I'm working on upstream our Tegra soc_camera host driver. But found
> the soc_camera framework is not fully supporting Device Tree probing,
> am I wrong about that?

Mostly correct, yes, currently soc-camera doesn't support device-tree 
probing.

> While in upstream Tegra kernel, we only support
> DT probing and there is no board files.
> 
> Current soc_camera framework needs to put soc_camera_link information
> in a board file and build up soc-camera-pdrv platform_device, then
> finally register this soc-camera-pdrv platform_device.
> 
> For the host driver, we can do DT probing but for i2c soc_camera
> sensor driver I failed to find any DT probing in upstream kernel. So
> how to do that without an board file but use DT for this whole thing?
> 
> Can we use DT like this?
> DTB file will pass those I2C, clock, regulator, GPIO information to
> host driver. During host driver DT probing, we dynamically create
> soc-camera-pdrv platform_device and soc_camera_link then register
> them. Then the rest of the thing should be the same as None-DT
> probing.

I've worked on soc-camera DT in the past, this might be the last published 
version

http://marc.info/?l=linux-sh&m=134875489304837&w=1

As you see, it's quite old. Since then a few things happened. Device tree 
support has been added to V4L2 (see 
Documentation/devicetree/bindings/media/video-interfaces.txt and other 
files in that directory for examples), it is based on asynchronous 
probing, which is also supported by the soc-camera core and some its 
host drivers (e.g.

commit 4dbfd040757b8bf22f4ac17e80b39c068061a16c
Author: Guennadi Liakhovetski <g.liakhovetski@xxxxxx>
Date:   Tue Jul 30 02:59:49 2013 -0300

    [media] V4L2: mx3_camera: add support for asynchronous subdevice registration

). So, what you should do, is add asynchronous probing support to your 
driver, add DT support to the soc-camera core, add it to your drivers. 
Also see drivers/media/v4l2-core/v4l2-of.c for helper functions, you 
should be using.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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