On Thu, May 16, 2013 at 11:12 AM, James Hogan <james.hogan@xxxxxxxxxx> wrote: > Hi Linus, > On 15/05/13 20:07, Linus Walleij wrote: >> On Tue, May 14, 2013 at 2:22 PM, James Hogan <james.hogan@xxxxxxxxxx> wrote: >> >>> I think that's the other way around, i.e. that's talking about mapping >>> several pingroups to the same function. The next paragraph is closer to >>> the problem: >>> >>> Documentation/pinctrl.txt >>>> - PINS for a certain FUNCTION using a certain PIN GROUP on a certain >>>> PIN CONTROLLER are provided on a first-come first-serve basis, so if some >>>> other device mux setting or GPIO pin request has already taken your physical >>>> pin, you will be denied the use of it. To get (activate) a new setting, the >>>> old one has to be put (deactivated) first. >>> >>> In my example the tft pingroup contains all the tft pins, but I might >>> want a particular pin inside that pingroup to never be controlled by the >>> mux (using the per-pin mux disable (SELECT) bits). >>> >>> So if I use pinmux I'd have something like: >>> * "tft" pingroup maps to "tft" function >>> * "tft_green0" pingroup (containing individual pin inside "tft" >>> pingroup) maps to "none" function to disable muxing (or the inverse, >>> with each pin in use mapping to "periph" to enable muxing). >>> in which case the pin has multiple muxes "controlling" it (even though >>> they're sort of nested). The above paragraph seems to condemn this >>> arrangement. >> >> So if this usecase is what you want to support, why don't you just >> exclude that one pin from the "tft" group and put it into another >> group? > > It's a very board specific thing (that was just one example). To > generalise your suggestion would make all muxing pingroups contain no > pins (which is perhaps accurate since the thing that's muxed by the > group is a set of internal signals that may be muxed out to pins via the > SELECT bits). Well there are different ways to skin this cat. Stephen usually says that if each pin can be muxed individually (such as if they each have a unique control register switching that very pin between different devices) then each pin should have its own pin group. Then you accumulate these groups into a state, there may be many of them. One group per pin is perfectly legal. Myself I've been soft on the issue. I think that is the hardware engineers designing the pin muxing have had certain usecases in mind, or (especially) if there are hardware restricts such that the mux from a system point of view can just be set if it is set on all pins in succession, we can define a group of pins for the usecase. You're making it sound like the one-group-per-pin is a more viable approach in your case and that will work, but myself I usually try to go over the usecases from a HW point of view and think which groups make sense to combine, and come up with a small set of groups that I combine with a function to get the right settings for a device. Please choose the solution you think fits your system best. However avoid falling into the combinatorial trap, pinctrl is not about listing all the possible *theoretical* combinations of pins in groups, that is mathematics. We're doing practical solutions here. Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
