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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Friday 05 October 2012 12:58:21 Guennadi Liakhovetski wrote:
> On Fri, 5 Oct 2012, Hans Verkuil wrote:
> > On Tue October 2 2012 12:13:20 Sylwester Nawrocki wrote:
> > > 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.

The OMAP3 ISP is on my to-do list, but that depends on the generic clock 
availability on the OMAP3, so I have to wait.

> > 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.

I agree that async I2C handling should have V4L2 core helpers, otherwise it's 
going to be pretty complex for ISP drivers.

-- 
Regards,

Laurent Pinchart