Re: [PATCH v3] pwm: pwm-samsung: Trigger manual update when disabling PWM

[Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>]

On 09/09/2021 12:10, 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@axis.com>
> ---
> 
> v2:
>  - Move fix above setting of disabled_mask
> 
> v3:
>  - Move up definition of __pwm_samsung_manual_update to avoid
>    declaration of the same
> 
>  drivers/pwm/pwm-samsung.c | 30 ++++++++++++++++++++++--------
>  1 file changed, 22 insertions(+), 8 deletions(-)
> 


Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>


Best regards,
Krzysztof