Re: [PATCH] pwm-pca9685: Allow any of the 16 PWMs to be used as a GPIO

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Wed, Oct 19, 2016 at 10:05:33PM +0200, Clemens Gruber wrote:
> > On Tue, Sep 20, 2016 at 05:40:56PM +0300, Mika Westerberg wrote:
> > > The PCA9685 controller has full on/off bit for each PWM channel. Setting
> > > this bit bypasses the PWM control and the line works just as it would be a
> > > GPIO. Furthermore in Intel Galileo it is actually used as GPIO output for
> > > discreet muxes on the board.
> > > 
> > > This patch adds GPIO output only support for the driver so that we can
> > > control the muxes on Galileo using standard GPIO interfaces available in
> > > the kernel. GPIO and PWM functionality is exclusive so only one can be
> > > active at a time on a single PWM channel.
> > > 
> > > Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> 
> Hi Mika,
> 
> what do you think about implementing this on a higher level / in the pwm
> core instead of adding it to one specific pwm driver?

I originally thought about it but since there is only one driver I'm
aware of that actually needs this functionality (because of how Galileo
uses the PWM outputs), I decided to add it only to this driver.

> The fact that the PCA9685 bypasses PWM control if the full on/off bits
> are set is beneficial but not a requirement to work as a GPIO.
> Every pwm output could act as GPIO if the duty cycle is set to 0%/100%.

Yes, that's right.

> The pwm-pca9685 driver does already clear both OFF registers and sets
> the ON register depending upon the duty cycle being at 0% or 100%.
> So it might work without making any changes to specific pwm drivers and
> it would then be available for all pwm chips.

I'm fine adding it to PWM core instead if Thierry does not have
objections. However, do you think there is actual use for this outside
of Galileo?