On Tue, Nov 17, 2009 at 12:47 AM, David Brownell <david-b@xxxxxxxxxxx> wrote: > On Friday 13 November 2009, Grant Likely wrote: >> Right now, I don't >> see a fundamental difference is between GPIO and PWM pin management. >> It is essentially the same problem, and in many cases PWM pins can >> also be used as GPIOs. > > Pin management for a given SoC is going to be relevant to setting > every signal, no matter what peripheral it's associated with. The > same argument applies to an MDIO bus, I2C, 1-wire, and more. > > And I don't buy it in those cases either. > > >> I think the question should be flipped around; >> rather than asking for a compelling reason for them to be merged; I >> want to know the compelling reason to keep them separate. What is the >> fundamental difference that keeps them apart? > > PWM is about periodic signal generation without CPU intervention. > > GPIO is about explicit CPU management/interrogation of single > signals. Can also be viewed from the perspective: It is about putting a pin into a particular state until I explicitly tell you to change it. Whether that state be a GPIO input, a GPIO high, a GPIO low, or a PWM periodic. >> What I would like to see is the PWM functions added to the GPIO API. > > No. If you want a pin mux interface, come up with one of them. > > It shouldn't be a PWM interface, a GPIO interface, an I2C interface, > a SPI interface, an MDIO interface, a 1-wire interface ... or any of > dozens of other things. It'd be purely for pinmux. I'm not talking about a pin mux interface. I'm talking about discrete controllable entities. I agree that pin muxing is an entirely different scope. I'm also not talking about layers on top of the GPIO. 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. 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. g. -- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd. -- 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
