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

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Date:	Wed, 3 Jun 2009 11:38:35 -0400
From:	Jon Smirl <jonsmirl@...il.com>
To:	avorontsov@...mvista.com
Cc:	Stefan Strobl <nst@...sys.de>, ppc-dev <linuxppc-dev@...abs.org>,
	linux-kernel@...r.kernel.org
Subject: Re: PWM class? (was: Re: MPC52xx simple GPIO support)

On Wed, Jun 3, 2009 at 9:22 AM, Anton Vorontsov
<avorontsov@...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.

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
> email: cbouatmailru@...il.com
> irc://irc.freenode.net/bd2
> --
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-- 
Jon Smirl
jonsmirl@...il.com
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