On 08/09/2021 16:27, Mårten Lindahl wrote:
> When duty-cycle is at full level (100%), the TCNTn and TCMPn registers
> needs to be flushed in order to disable the signal. The PWM manual does
> not say anything about this, but states that only clearing the TCON
> auto-reload bit should be needed, and this seems to be true when the PWM
> duty-cycle is not at full level. This can be observed on an Axis
> ARTPEC-8, by running:
>
> echo <period> > pwm/period
> echo <period> > pwm/duty_cycle
> echo 1 > pwm/enable
> echo 0 > pwm/enable
>
> Since the TCNTn and TCMPn registers are activated when enabling the PWM
> (setting TCON auto-reload bit), and are not touched when disabling the
> PWM, the double buffered auto-reload function seems to be still active.
> Lowering duty-cycle, and restoring it again in between the enabling and
> disabling, makes the disable work since it triggers a reload of the
> TCNTn and TCMPn registers.
>
> Fix this by securing a reload of the TCNTn and TCMPn registers when
> disabling the PWM and having a full duty-cycle.
>
> Signed-off-by: Mårten Lindahl <marten.lindahl@xxxxxxxx>
> ---
> drivers/pwm/pwm-samsung.c | 25 +++++++++++++++++++++----
> 1 file changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c
> index f6c528f02d43..7d90652402a0 100644
> --- a/drivers/pwm/pwm-samsung.c
> +++ b/drivers/pwm/pwm-samsung.c
> @@ -105,6 +105,9 @@ struct samsung_pwm_chip {
> static DEFINE_SPINLOCK(samsung_pwm_lock);
> #endif
>
> +static void __pwm_samsung_manual_update(struct samsung_pwm_chip *chip,
> + struct pwm_device *pwm);
> +
> static inline
> struct samsung_pwm_chip *to_samsung_pwm_chip(struct pwm_chip *chip)
> {
> @@ -278,17 +281,21 @@ static void pwm_samsung_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>
> our_chip->disabled_mask |= BIT(pwm->hwpwm);
>
> + /*
> + * In case the PWM is at 100% duty cycle, force a manual
> + * update to prevent the signal from staying high.
> + */
> + if (readl(our_chip->base + REG_TCMPB(pwm->hwpwm)) == (u32)-1U)
> + __pwm_samsung_manual_update(our_chip, pwm);
I did not test it but looks reasonable. Just please move it above
setting "our_chip->disabled_mask", so the code will be close to
pwm_samsung_enable.
Best regards,
Krzysztof
