[PATCH] pwm: pwm-samsung: Trigger manual update when disabling PWM

[Krzysztof Kozlowski]

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 at axis.com>
> ---
>  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