On Fri, Oct 28, 2022 at 01:33:56PM +0100, Jon Hunter wrote:
> When dynamically scaling the PWM clock, the function
> dev_pm_opp_set_rate() may set the PWM clock to a rate that is lower than
> what is required. The clock rate requested when calling
> dev_pm_opp_set_rate() is the minimum clock rate that is needed to drive
> the PWM to achieve the required period. Hence, if the actual clock
> rate is less than the requested clock rate, then the required period
> cannot be achieved and configuring the PWM fails. Fix this by
> calling clk_round_rate() to check if the clock rate that will be provided
> is sufficient and if not, double the required clock rate to ensure the
> required period can be attained.
>
> Fixes: 8c193f4714df ("pwm: tegra: Optimize period calculation")
> Signed-off-by: Jon Hunter <jonathanh@xxxxxxxxxx>
> ---
> Changes since V1:
> - Multiplied the required_clk_rate by 2 instead of adding 1 to the
> PWM_DUTY_WIDTH and recalculating the rate. Overall rate should be
> similar.
> - Updated comment based upon Uwe's feedback.
>
> drivers/pwm/pwm-tegra.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/drivers/pwm/pwm-tegra.c b/drivers/pwm/pwm-tegra.c
> index b05ea2e8accc..6fc4b69a3ba7 100644
> --- a/drivers/pwm/pwm-tegra.c
> +++ b/drivers/pwm/pwm-tegra.c
> @@ -148,6 +148,17 @@ static int tegra_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> required_clk_rate = DIV_ROUND_UP_ULL(NSEC_PER_SEC << PWM_DUTY_WIDTH,
> period_ns);
>
> + if (required_clk_rate > clk_round_rate(pc->clk, required_clk_rate))
> + /*
> + * required_clk_rate is a lower bound for the input
> + * rate; for lower rates there is no value for PWM_SCALE
> + * that yields a period less than or equal to the
> + * requested period. Hence, for lower rates, double the
> + * required_clk_rate to get a clock rate that can meet
> + * the requested period.
> + */
> + required_clk_rate *= 2;
Acked-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Thanks
Uwe
> +
> err = dev_pm_opp_set_rate(pc->dev, required_clk_rate);
> if (err < 0)
> return -EINVAL;
> --
> 2.25.1
>
>
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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