On Thu, Jun 11, 2009 at 04:00:51PM -0600, Grant Likely wrote: > 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.
I didn't say that we should duplicate gpiolib. I said that we might borrow some ideas. ;-) > 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. Jon Smirl found that there were already some efforts put into making generic PWM class: http://thread.gmane.org/gmane.linux.kernel.embedded/1160 Briefly looking, the class is pretty cool. Somebody should just continue this work. > 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. I don't think David Brownell will like this idea. But who knows... maybe. Thanks, -- Anton Vorontsov email: cbouatmai...@gmail.com irc://irc.freenode.net/bd2 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
