On Fri, 10 Jun 2016, Boris Brezillon wrote: > > Basically, in the general case, the controller can handle a matrix of > > nand flash chips. There can be a number of banks, each of which can > > have a number of individual CS lines. For the (in this case academic) > > case of 3 banks and 4 chip selects per bank, there would be a total of > > 3 x 4 = 12 CS lines. > > > > For the IP configuration the driver was written for, there are only 2 > > CS lines, and we can configure if they are to be viewed by the > > controller as 2 CS lines within the same single bank, or 2 separate > > banks with one CS each. This is what the DT property is intended to > > express. It basically translates directly into a register write in the > > IP. > > Okay, got it. I guess we should just expose the chip select in a linear > way (3 banks of 4 CS means the controller should support up to 12 > chips), unless you really have a way to change the CS pins routing > internally. When I go through the driver I will also revisit this and give it some more thought if there's a set of bindings which would make sense both for the case we have now and for a general configuration of the IP. > > Yes, that makes sense of course, but what if someone would want to > > override the automatic settings, for whatever reason, using an > > optional DT property? I can think of several reasons either way, > > that's why I'm asking. > > You mean reducing the timings because the board design prevents using > the highest supported mode for example? That would actually be a valid > use case, and I guess we could make a generic property for that > (without the vendor prefix). Yes, either that, or if the automatic selection fails for some reason, say in a given case we know that the chips we are using support mode 2 timing, but one of them gets misidentified as mode 0. Sure, that is a bug and should be fixed of course, but I can imagine commercial situations where it may not be feasable to update the kernel, but where a new DT would be ok. /Ricard -- Ricard Wolf Wanderlöf ricardw(at)axis.com Axis Communications AB, Lund, Sweden www.axis.com Phone +46 46 272 2016 Fax +46 46 13 61 30 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
