On Wed, Jun 3, 2009 at 7:22 AM, Anton Vorontsov<avoront...@ru.mvista.com> wrote: > On Wed, Jun 03, 2009 at 02:42:26PM +0200, Stefan Strobl wrote: > [...] >> The led class provides support for setting the brightness, which >> obviously the gpio driver doesn't support. The hardware (mpc52xx_gpt) >> would support it in PWM mode though. I'm now wandering how this could be >> best implemented. >> >> 1) - Create some PWM class similar to the GPIO class >> - Add support for PWM mode in mpc52xx_gpt.c that uses that PWM class >> - And add an interface for the LED to use the PWM class >> >> 2) - Create an LED driver that accesses the mpc52xx_gpt directly. >> >> I think I would be overwhelmed trying to implement (1) but am confident >> to do (2). What do you think is the right approach? > > I'd suggest creating a generic PWM class, i.e. PWMLIB, alike to > GPIOLIB. (2) can be an acceptable approach for now, but for the > long-term solution (1) is the way to go. > > The non-lib PWM API is already there, see include/linux/pwm.h, > and arch/arm/mach-pxa/pwm.c as an implementation example. > > Note that PXA implementation is SOC-specific, which is not very > good. > > So I'd suggest creating drivers/pwm/pwmlib.c, borrowing > ideas from gpiolib. And then we can reuse drivers/leds/leds-pwm.c > driver (of course, after adding appropriate OF code into it).
Ugh. The referenced pwm api is about as trivial as it gets; it is an anonymous context pointer (anonymous struct pwm_device *) with a set of accessor functions. PWMs are also not nearly as common as GPIO pins, and I am not interested in gpiolib being duplicated for PWMs, at least not until there are more that just two examples of use to draw from. If anything, I'd rather struct pwm_device be non-anonymous and contain a set of ops which call directly into the driver. That way is at least multiplatform friendly. I don't think the gpio API is the example to follow here. But even then I think it is premature to try and define a PWM api. Personally, I'd modify mpc52xx_gpt to export its own PWM interface for the time being using the existing GPIO infrastructure to find the appropriate pin. If you do decide to do a generic PWM api, then I think the way to go is to build it as an extension to gpiolib. Cheers, g. -- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
