Guennadi and Hans, <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. AFAIK, There is not such thing as sampling edge configuration for MIPI Receivers, and the polarities DO matter, since it's a differential signal. > > Ok, this is much better! I'm still not perfectly happy having to punish > all just for the sake of a couple of broken boards, but I can certainly > much better live with this, than with having to hard-code each and every > bit. Thanks, Hans! > > So, I think, we can proceed with this, let's see the code now, shall we?;) > > Currently soc-camera auto-configures the following parameters: > > hsync polarity > vsync polarity > data polarity > master / slave mode > data bus width > pixel clock polarity > > (see include/media/soc_camera.h::soc_camera_bus_param_compatible() and > drivers/media/video/soc_camera.c::soc_camera_apply_sensor_flags()). > Removing the pixclk polarity, the rest we can use as a basis for a new > subdev-based implementation. Don't we need to move this out from soc_camera and make it available in v4l2_subdev ops? (I'm talking about both parallel and the "new" MIPI support) That way both SoC_Camera, and Media Controller frameworks can use that. Regards, Sergio > > Thanks > Guennadi > > > Unfortunately, if a subdev is set to 'sample at rising edge', then that > does > > not necessarily mean that the host should sample at the same edge. > Depending > > on the clock line routing and the integrity of the clock signal the host > may > > actually have to sample on the other edge. And yes, I've seen this. > > > > Anyway, this has been discussed to death already. I am very much opposed > to > > negotiating the sampling edge. During the Helsinki meeting in June last > year > > we decided to do this via platform data (see section 7 in the meeting > > minutes: http://www.linuxtv.org/news.php?entry=2010-06-22.mchehab). > > > > I will formally NACK attempts to negotiate this. Mauro is of course free > to > > override me. > > > > Something simple like this for subdev platform_data might be enough: > > > > struct v4l2_bus_config { > > /* 0 - sample at falling edge, 1 - sample at rising edge */ > > unsigned edge_pclock:1; > > /* 0 - host should use the same sampling edge, 1 - host should > use the > > other sampling edge */ > > unsigned host_invert_edge_pclock:1; > > }; > > > > The host can query the bus configuration and the subdev will return: > > > > edge = host_invert_edge_pclock ? !edge_pclock : edge_pclock; > > > > We might want to add bits as well to describe whether polarities are > inverted. > > > > This old RFC gives a good overview of the possible polarities: > > > > http://www.mail-archive.com/linux-media@vger.kernel.org/msg09041.html > > > > Regards, > > > > Hans > > > > > I personally like the Stanimir's proposal as the parameters to be > negotiated > > > are pretty dynamic. Only the number of lanes could be problematic as > not all > > > lanes might be routed across different boards. Perhaps we should > consider specifying > > > an AUTO value for some negotiated parameters. Such as in case of an > attribute that > > > need to be fixed on some boards or can be fully negotiated on others, > a fixed > > > value or "auto" could be respectively set up in the host's > platform_data. This could > > > be used to override some parameters in the host driver if needed. > > > > > > IMHO, as long as we negotiate only dynamic parameters there should be > no special > > > issues. > > > > > > Regards, > > > Sylwester > > > > > > > about this if it wasn't for the fact that soc-camera doesn't do this > but instead > > > > negotiates it. Obviously, it isn't a pleasant prospect having to > change all that. > > > > > > > > Normally this would be enough of an argument for me to just > negotiate it. The > > > > reason that I don't want this in this particular case is that I know > from > > > > personal experience that incorrect settings can be extremely hard to > find. > > > > > > > > I also think that there is a reasonable chance that such bugs can > happen. Take > > > > a scenario like this: someone writes a new host driver. Initially > there is only > > > > support for positive polarity and detection on the rising edge, > because that's > > > > what the current board on which the driver was developed supports. > This is quite > > > > typical for an initial version of a driver. > > > > > > > > Later someone adds support for negative polarity and falling edge. > Suddenly the > > > > polarity negotiation on the previous board results in negative > instead of positive > > > > which was never tested. Now that board starts producing pixel errors > every so > > > > often. And yes, this type of hardware problems do happen as I know > from painful > > > > experience. > > > > > > > > Problems like this are next to impossible to debug without the aid > of an > > > > oscilloscope, so this isn't like most other bugs that are relatively > easy to > > > > debug. > > > > > > > > It is so much easier just to avoid this by putting it in platform > data. It's > > > > simple, unambiguous and above all, unchanging. > > > > > > > > Regards, > > > > > > > > Hans > > > > > > > >> > > > >> Thanks > > > >> Guennadi > > > >> --- > > > >> Guennadi Liakhovetski, Ph.D. > > > >> Freelance Open-Source Software Developer > > > >> http://www.open-technology.de/ > > > >> -- > > > >> To unsubscribe from this list: send the line "unsubscribe linux- > media" in > > > >> the body of a message to majord...@vger.kernel.org > > > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > > >> > > > > > > > > > > > > > > -- > > Hans Verkuil - video4linux developer - sponsored by Cisco > > > > --- > Guennadi Liakhovetski, Ph.D. > Freelance Open-Source Software Developer > http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
