[PATCH 05/14] media: add a V4L2 OF parser

[Guennadi Liakhovetski]

On Fri, 5 Oct 2012, Hans Verkuil wrote:

> On Tue October 2 2012 12:13:20 Sylwester Nawrocki wrote:
> > Hi Guennadi,
> > 
> > On 10/02/2012 11:49 AM, Guennadi Liakhovetski wrote:
> > >>> +	if (!of_property_read_u32_array(node, "data-lanes", data_lanes,
> > >>> +					ARRAY_SIZE(data_lanes))) {
> > >>> +		int i;
> > >>> +		for (i = 0; i<  ARRAY_SIZE(data_lanes); i++)
> > >>> +			link->mipi_csi_2.data_lanes[i] = data_lanes[i];
> > >>
> > >> It doesn't look like what we aimed for. The data-lanes array is supposed
> > >> to be of variable length, thus I don't think it can be parsed like that. 
> > >> Or am I missing something ? I think we need more something like below 
> > >> (based on of_property_read_u32_array(), not tested):
> > > 
> > > Ok, you're right, that my version only was suitable for fixed-size arrays, 
> > > which wasn't our goal. But I don't think we should go down to manually 
> > > parsing property data. How about (tested;-))
> > > 
> > > 	data = of_find_property(node, "data-lanes", NULL);
> > > 	if (data) {
> > > 		int i = 0;
> > > 		const __be32 *lane = NULL;
> > > 		do {
> > > 			lane = of_prop_next_u32(data, lane, &data_lanes[i]);
> > > 		} while (lane && i++ < ARRAY_SIZE(data_lanes));
> > > 		link->mipi_csi_2.num_data_lanes = i;
> > > 		while (i--)
> > > 			link->mipi_csi_2.data_lanes[i] = data_lanes[i];
> > > 	}
> > 
> > Yes, that looks neat and does what it is supposed to do. :) Thanks!
> > For now, I'll trust you it works ;)
> > 
> > With regards to the remaining patches, it looks a bit scary to me how
> > complicated it got, perhaps mostly because of requirement to reference
> > host devices from subdevs. And it seems to rely on the existing SoC
> > camera infrastructure, which might imply lot's of work need to be done
> > for non soc-camera drivers. But I'm going to take a closer look and
> > comment more on the details at the corresponding patches.
> 
> I have to say that I agree with Sylwester here. It seems awfully complicated,
> but I can't really put my finger on the actual cause.

Well, which exactly part? The V4L2 OF part is quite simple.

> It would be really
> interesting to see this implemented for a non-SoC device and to compare the
> two.

Sure, volunteers? ;-) In principle, if I find time, I could try to convert 
sh_vou, which is also interesting, because it's an output driver.

> One area that I do not yet completely understand is the i2c bus notifications
> (or asynchronous loading or i2c modules).
> 
> I would have expected that using OF the i2c devices are still initialized
> before the host/bridge driver is initialized. But I gather that's not the
> case?

No, it's not. I'm not sure, whether it depends on the order of devices in 
the .dts, but, I think, it's better to not have to mandate a certain order 
and I also seem to have seen devices being registered in different order 
with the same DT, but I'm not 100% sure about that.

> If this deferred probing is a general problem, then I think we need a general
> solution as well that's part of the v4l2 core.

That can be done, perhaps. But we can do it as a next step. As soon as 
we're happy with the OF implementation as such, we can commit that, 
possibly leaving soc-camera patches out for now, then we can think where 
to put async I2C handling.

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