Messages in this thread | | | Date | Wed, 18 Jan 2017 14:53:25 +0100 | From | Clemens Gruber <> | Subject | Re: [PATCH 2/2] pwm: pca9685: fix prescaler initialization |
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On Wed, Jan 18, 2017 at 01:09:24PM +0200, Andy Shevchenko wrote: > On Wed, 2017-01-18 at 11:57 +0100, Thierry Reding wrote: > > On Tue, Dec 13, 2016 at 04:52:51PM +0100, Clemens Gruber wrote: > > > Until now, we assumed that the period is the hardware default of > > > 1/200Hz > > > at probe time, but if the period was changed and the user reboots, > > > this > > > assumption is wrong. > > > > > > Solution: Check if the prescaler is set to the hardware default. If > > > not, > > > reprogram the prescaler at first configuration. > > AFAIU the PWM is off until user space or kernel user enables it > explicitly after reboot. Is it correct?
Yes, but the period could be different, maybe modified in the bootloader or at a previous boot without hardware reset in between. (We do not send a SWRST to the chip, so the period register could be different)
Until now, we assumed it is always 1/200 Hz and skipped the lengthy prescale configuration (put chip into sleep mode, set prescaler, go out of sleep mode, udelay for 0.5ms until the oscillator is back up) if the user wants a period of 1/200 Hz.
With this patch, we check if it is in fact set to the hardware default. If not, we set pca->period_ns to 0 which leads to changing the prescaler in the next call to pca9685_pwm_config.
Thanks, Clemens
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