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Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization

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On Thu, Jan 19, 2017 at 02:34:39PM +0200, Andy Shevchenko wrote:
> On Wed, 2017-01-18 at 15:25 +0100, Clemens Gruber wrote:
> > Yes, that's what this patch tries to solve by verifying that the
> > external setting (the prescale register) is set to its hardware
> > default
> > value of 0x1E (corresponding to a period of 1/200 Hz).
> > If it is not 0x1E, the driver will reconfigure the prescaler according
> > to the desired period at the time of the next configuration.
> 
> Yes, and my question is what is possible go wrong if you just enforce
> prescaler to be 1/200Hz?

If we enforce a default of 1 / 200 Hz, we have to go through the SLEEP
mode and udelay for 0.5ms once for our default and then again for the
user, if he does not want a period of 1 / 200 Hz.
-> Number of prescaler changes: 1 or 2

I think it is better as it is now + my patch applied: We verify if the
prescaler is already set to 1 / 200 Hz.
Then, as soon as the user configures his PWM channels, we either do not
have to change the prescaler at all (if he wants 1 / 200 Hz) or do it
once at the time of configuration.
-> Number of prescaler changes: 0 or 1

What's the advantage of enforcing the prescaler to 1 / 200 Hz in the
probe function when we do not know yet if 1 / 200 Hz is the period the
user is going to configure?

Thanks,
Clemens

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Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Thierry Reding <thierry.reding@gmail.com> - 2017-01-18 12:10 +0100
  Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Andy Shevchenko <andriy.shevchenko@linux.intel.com> - 2017-01-18 12:20 +0100
    Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Clemens Gruber <clemens.gruber@pqgruber.com> - 2017-01-18 15:00 +0100
      Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Andy Shevchenko <andriy.shevchenko@linux.intel.com> - 2017-01-18 15:10 +0100
        Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Clemens Gruber <clemens.gruber@pqgruber.com> - 2017-01-18 15:30 +0100
          Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Andy Shevchenko <andriy.shevchenko@linux.intel.com> - 2017-01-19 13:40 +0100
            Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Clemens Gruber <clemens.gruber@pqgruber.com> - 2017-01-19 16:00 +0100
              Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Andy Shevchenko <andriy.shevchenko@linux.intel.com> - 2017-01-19 17:20 +0100
                Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Clemens Gruber <clemens.gruber@pqgruber.com> - 2017-01-19 18:00 +0100
                Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Andy Shevchenko <andy.shevchenko@gmail.com> - 2017-01-19 18:10 +0100
                Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Thierry Reding <thierry.reding@gmail.com> - 2017-01-20 07:40 +0100
                Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Andy Shevchenko <andriy.shevchenko@linux.intel.com> - 2017-01-20 11:10 +0100
                Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization Clemens Gruber <clemens.gruber@pqgruber.com> - 2017-01-25 19:10 +0100

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