[PATCH] pwm: tiehrpwm: Clear period on disable to allow reconfiguration

[PATCH] pwm: tiehrpwm: Clear period on disable to allow reconfiguration

[A. Sverdlin]

From: Alexander Sverdlin <alexander.sverdlin@siemens.com>

Both channels share one period register, so ehrpwm_pwm_config() rejects a
period differing from the sibling's period_cycles[]. That value was cleared
only in .free(), not in .disable(), so a stopped channel kept blocking the
sibling from switching to a new frequency. Clear it in .disable() too.

Testcase:

  cd /sys/class/pwm/pwmchip0; echo 0 > export; echo 1 > export
  for p in pwm0 pwm1; do
    echo 1000000 > $p/period; echo 500000 > $p/duty_cycle
    echo 1 > $p/enable; echo 0 > $p/enable; echo 2000000 > $p/period
  done
  echo 1 > pwm0/enable	# before: -EINVAL, after: succeeds

Fixes: 01b2d4536f02 ("pwm: pwm-tiehrpwm: Fix conflicting channel period setting")
Cc: stable@vger.kernel.org
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
---
 drivers/pwm/pwm-tiehrpwm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pwm/pwm-tiehrpwm.c b/drivers/pwm/pwm-tiehrpwm.c
index 3a53489f0b982..e3407d0a1f7fe 100644
--- a/drivers/pwm/pwm-tiehrpwm.c
+++ b/drivers/pwm/pwm-tiehrpwm.c
@@ -358,6 +358,9 @@ static void ehrpwm_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
 
 	/* Disable clock on PWM disable */
 	pm_runtime_put_sync(pwmchip_parent(chip));
+
+	/* A disabled channel must not constrain the sibling's period */
+	pc->period_cycles[pwm->hwpwm] = 0;
 }
 
 static void ehrpwm_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
-- 
2.55.0

Re: [PATCH] pwm: tiehrpwm: Clear period on disable to allow reconfiguration

[Uwe Kleine-König]

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Hello Alexander,

On Tue, Sep 29, 2026 at 02:08:02PM +0200, A. Sverdlin wrote:
> From: Alexander Sverdlin <alexander.sverdlin@siemens.com>
> 
> Both channels share one period register, so ehrpwm_pwm_config() rejects a
> period differing from the sibling's period_cycles[]. That value was cleared
> only in .free(), not in .disable(), so a stopped channel kept blocking the
> sibling from switching to a new frequency. Clear it in .disable() too.
> 
> Testcase:
> 
>   cd /sys/class/pwm/pwmchip0; echo 0 > export; echo 1 > export
>   for p in pwm0 pwm1; do
>     echo 1000000 > $p/period; echo 500000 > $p/duty_cycle
>     echo 1 > $p/enable; echo 0 > $p/enable; echo 2000000 > $p/period
>   done
>   echo 1 > pwm0/enable	# before: -EINVAL, after: succeeds
> 
> Fixes: 01b2d4536f02 ("pwm: pwm-tiehrpwm: Fix conflicting channel period setting")
> Cc: stable@vger.kernel.org
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
> ---
>  drivers/pwm/pwm-tiehrpwm.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/pwm/pwm-tiehrpwm.c b/drivers/pwm/pwm-tiehrpwm.c
> index 3a53489f0b982..e3407d0a1f7fe 100644
> --- a/drivers/pwm/pwm-tiehrpwm.c
> +++ b/drivers/pwm/pwm-tiehrpwm.c
> @@ -358,6 +358,9 @@ static void ehrpwm_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>  
>  	/* Disable clock on PWM disable */
>  	pm_runtime_put_sync(pwmchip_parent(chip));
> +
> +	/* A disabled channel must not constrain the sibling's period */
> +	pc->period_cycles[pwm->hwpwm] = 0;
>  }
>  
>  static void ehrpwm_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)

That looks right, applied to

https://git.kernel.org/pub/scm/linux/kernel/git/ukleinek/linux.git pwm/for-next

as merge window material.

Looking at the driver, the check for the sibling running could be
weakend a bit. So if the restriction by the other channel only results
in a smaller period, configuration could continue.

(But if you're looking for something to do, better invest the time and
convert the driver to waveform.)

Thanks,
Uwe

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