On Wednesday, February 23, 2011 17:14:41 Laurent Pinchart wrote: > On Wednesday 23 February 2011 17:02:57 Hans Verkuil wrote: > > On Wednesday, February 23, 2011 16:30:42 Laurent Pinchart wrote: > > > On Wednesday 23 February 2011 15:06:49 Aguirre, Sergio wrote: > > > > <snip> > > > > > > > > > > The only static data I am concerned about are those that affect > > > > > > signal integrity. > > > > > > > > > > > > After thinking carefully about this I realized that there is really > > > > > > only one setting that is relevant to that: the sampling edge. The > > > > > > polarities do not matter in this. > > > > > > > > I respectfully disagree. > > > > > > So do I. Sampling edge is related to polarities, so you need to take both > > > into account. > > > > When you switch polarity for data/field/hsync/vsync signals on a simple bus > > you just invert whether a 1 bit is output as high or low voltage. So you > > just change the meaning of the bit. This does not matter for signal > > integrity, since you obviously have to be able to sample both low and high > > voltages. It is *when* you sample that can have a major effect. > > When you switch the polarity you will likely have to sample on the opposite > edge. If, for signal integrity reasons, you can only sample on a given edge, > you will want to use a fixed polarity and not negotiate it. You are confusing clock polarity (which is relevant) with data, field, hsync and vsync polarities which just invert the meaning of those pins. I wish I had a whiteboard to draw it, much easier to explain that way. > > Given the very small number of parameters that are negotiated by soc-camera at > the moment, I'm very much in favour of hardcoding all of them in platform data > and just adding a g_interface_parms subdev operation. Just for the record: I have no problem with hardcoding these polarities. After all, that was my original idea. But they can be negotiated as well. Regards, Hans > > > This might be different for differential clocks. I have no experience with > > this, so I can't say anything sensible about that. > > -- > Regards, > > Laurent Pinchart > > -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
