Re: PWM class? (was: Re: MPC52xx simple GPIO support)

On Wed, Jun 3, 2009 at 9:22 AM, Anton Vorontsov
[off-list ref] wrote:

On Wed, Jun 03, 2009 at 02:42:26PM +0200, Stefan Strobl wrote:
[...]

quoted

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
=A0 =A0- Add support for PWM mode in mpc52xx_gpt.c that uses that PWM cl=

ass

quoted

=A0 =A0- 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.

What happened to this one?

http://ozlabs.org/pipermail/linuxppc-dev/2008-October/063562.html

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).

Sure, as you've said, it could be quite boringly to implement,
could take quite some time to pass all review cycles etc.
But someday someone will have to do this. :-)

--
Anton Vorontsov
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Jon Smirl
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