Re: Determining wich PWM to use

[Thierry Reding <thierry.reding@gmail.com>]

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On Sat, Jul 27, 2013 at 12:18:24PM +0200, Johannes Thumshirn wrote:
> Hi list,
> 
> I'm currently working on a pwm driver for the BCM2853 (the SoC used on the
> RaspberryPi). It has two PWM modules, so my question is, how do I determine
> which PWM to use in the .enable, .disable and .configure functions?

It depends on what you mean by "two PWM modules". Does it have one
controller with two PWM outputs or does it have two controllers with one
or more outputs?

If you have one controller with multiple outputs, which seems to be the
case looking at the driver, then the struct pwm_device's .hwpwm field
contains the per-chip index of the PWM channel.

> If someone wants to have have a look at the preliminary code (far from being
> submittable and only compile tested) it can be found here:
> 
> https://github.com/morbidrsa/linux/blob/rpi-pwm/drivers/pwm/pwm-bcm2835.c

From a quick glance that looks pretty good already. Feel free to send it
to the mailing list for review anytime.

> 2nd short question, is it considered good practice to encapsulate registers in
> structs? I've seen this a lot on powerpc code.

It's not very common. I certainly prefer the standard way of using
writel(value, base + offset) and readl(base + offset), or a variation of
that using driver-specific accessors such as you've done in the above-
mentioned code.

Thierry

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