[Intel-gfx] [PATCH v2 04/15] pwm: lpss: Fix off by one error in base_unit math in pwm_lpss_prepare()

[Andy Shevchenko]

On Sun, Jun 07, 2020 at 08:18:29PM +0200, Hans de Goede wrote:
> According to the data-sheet the way the PWM controller works is that
> each input clock-cycle the base_unit gets added to a N bit counter and
> that counter overflowing determines the PWM output frequency.
> 
> So assuming e.g. a 16 bit counter this means that if base_unit is set to 1,
> after 65535 input clock-cycles the counter has been increased from 0 to
> 65535 and it will overflow on the next cycle, so it will overflow after
> every 65536 clock cycles and thus the calculations done in
> pwm_lpss_prepare() should use 65536 and not 65535.
> 
> This commit fixes this. Note this also aligns the calculations in
> pwm_lpss_prepare() with those in pwm_lpss_get_state().

This one sounds like a bug which I have noticed on Broxton (but thought as a
hardware issue). In any case it has to be tested on various platforms to see
how it affects on them.

-- 
With Best Regards,
Andy Shevchenko