Grant Likely wrote: > I'm talking about discrete controllable entities. At the extreme, I see discrete, single-pin GPIO as being a degenerate case of PWM: only 0% or 100% duty cycle e.g. one-bit granularity, a single output, and no dependencies with any other channels or pins. But the perspectives of the two groups of users are completely different, so I don't see any advantage to having a combined user-facing API. > I'm talking about the management code to obtain a reference to > the pin your interested in. There is a non-trivial amount of code > associated with getting a reference to a pin and the behaviour > required is largely identical between GPIO and PWM. True, but anything involving pins has to be dealt with at the platform level. And the general approach for that so far is that the board's startup code sets the pins how it wants them, and the peripheral drivers more or less assume that things are as they should be when it comes time to activate the peripherals themselves. Anything more sophisticated than that and you prevent the kind of reuse that's taking place now between AVR32 and AT91, for example. Maybe that's an opportunity for improvement: an API for pin reservation, that GPIO, PWM and other platform-oriented drivers could use to request the pins that they want. A kind of common version of the OMAP mux management code, if you will. But I don't think such an API would be all that useful for GPIO- and PWM-related scenarios. Out of necessity, PWM and GPIO are very specific to the board hardware, and on-the-fly pin configuration changes aren't possible: either the hardware needs that pin to be an output, or it doesn't. You can't make that decision at runtime because you'd probably have to swap out or add resistors, drivers, etc. The software to do *that* would be.... tricky. :) > I don't want to see a new subsystem that largely does the exact same job, but is > different in subtle ways. I think it should either be a unified > PWM/GPIO pin management subsystem, or a common library used by each. > Where is there overlap? My PWM code is totally pin-agnostic, at least for the drivers I've worked with so far. And I'm not aware of any GPIO chip drivers that deal with pin multiplexing, either. Not saying there aren't any, only that I haven't seen them. It's a nice idea in the abstract, but I sure don't see how to make it work well enough in practice to be worth the effort. I'm not saying it can't be done, just that it isn't my focus. Yours? :) b.g. -- Bill Gatliff bgat@xxxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
