On Sun, Aug 30, 2020 at 02:57:45PM +0200, Hans de Goede wrote: > The CRC PWM controller has a clock-divider which divides the clock with > a value between 1-128. But as can seen from the PWM_DIV_CLK_xxx > defines, this range maps to a register value of 0-127. > > So after calculating the clock-divider we must subtract 1 to get the > register value, unless the requested frequency was so high that the > calculation has already resulted in a (rounded) divider value of 0. > > Note that before this fix, setting a period of PWM_MAX_PERIOD_NS which > corresponds to the max. divider value of 128 could have resulted in a > bug where the code would use 128 as divider-register value which would > have resulted in an actual divider value of 0 (and the enable bit being > set). A rounding error stopped this bug from actually happen. This > same rounding error means that after the subtraction of 1 it is impossible > to set the divider to 128. Also bump PWM_MAX_PERIOD_NS by 1 ns to allow > setting a divider of 128 (register-value 127). > > Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx> > --- > Changes in v3: > - Introduce crc_pwm_calc_clk_div() here instead of later in the patch-set > to reduce the amount of churn in the patch-set a bit > --- > drivers/pwm/pwm-crc.c | 17 ++++++++++++++--- > 1 file changed, 14 insertions(+), 3 deletions(-) Acked-by: Thierry Reding <thierry.reding@xxxxxxxxx>
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