On Tue, Jan 05, 2021 at 02:42:28PM +0200, Baruch Siach wrote:
> The period is the sum of on and off values.
>
> Reported-by: Russell King <linux@xxxxxxxxxxxxxxx>
> Fixes: 757642f9a584e ("gpio: mvebu: Add limited PWM support")
> Signed-off-by: Baruch Siach <baruch@xxxxxxxxxx>
> ---
> drivers/gpio/gpio-mvebu.c | 16 ++++++----------
> 1 file changed, 6 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
> index 672681a976f5..ac7cb6d3702e 100644
> --- a/drivers/gpio/gpio-mvebu.c
> +++ b/drivers/gpio/gpio-mvebu.c
> @@ -679,17 +679,13 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
> regmap_read(mvpwm->regs, mvebu_pwmreg_blink_off_duration(mvpwm), &u);
> val = (unsigned long long) u * NSEC_PER_SEC;
> do_div(val, mvpwm->clk_rate);
> - if (val < state->duty_cycle) {
> + val += state->duty_cycle;
> + if (val > UINT_MAX)
> + state->period = UINT_MAX;
> + else if (val)
> + state->period = val;
> + else
> state->period = 1;
Are you sure this is the correct solution? Aren't you introducing
rounding errors?
The hardware will count to (on + off) clock ticks, so the right way
to convert that is to add the two together and then convert to
nanoseconds, which may result in a single rounding error. If you
convert each individually to nanoseconds, then you can end up with
two sets of rounding errors.
--
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