linux-kernel - Re: [PATCH v2 4/6] pwm: omap-dmtimer: Fix pwm disabling sequence

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Message-ID: <20200306181443.GJ37466@atomide.com>
Date:   Fri, 6 Mar 2020 10:14:43 -0800
From:   Tony Lindgren <tony@...mide.com>
To:     Lokesh Vutla <lokeshvutla@...com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        Sekhar Nori <nsekhar@...com>, Vignesh R <vigneshr@...com>,
        Sebastian Reichel <sre@...nel.org>
Subject: Re: [PATCH v2 4/6] pwm: omap-dmtimer: Fix pwm disabling sequence

* Lokesh Vutla <lokeshvutla@...com> [200228 09:58]:
> pwm_omap_dmtimer_disable() calls .stop callback which abruptly stops the
> timer counter. This doesn't complete the current pwm cycle and
> immediately disables the pwm. Instead disable the auto reload
> functionality which allows to complete the current pwm cycle and then
> disables the timer.
> 
> Signed-off-by: Lokesh Vutla <lokeshvutla@...com>
> ---
>  drivers/pwm/pwm-omap-dmtimer.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-omap-dmtimer.c b/drivers/pwm/pwm-omap-dmtimer.c
> index bc338619232d..89b3c25d02b8 100644
> --- a/drivers/pwm/pwm-omap-dmtimer.c
> +++ b/drivers/pwm/pwm-omap-dmtimer.c
> @@ -93,8 +93,16 @@ static void pwm_omap_dmtimer_disable(struct pwm_chip *chip,
>  {
>  	struct pwm_omap_dmtimer_chip *omap = to_pwm_omap_dmtimer_chip(chip);
>  
> +	/*
> +	 * Disable auto reload so that the current cycle gets completed and
> +	 * then the counter stops.
> +	 */
>  	mutex_lock(&omap->mutex);
> -	omap->pdata->stop(omap->dm_timer);
> +	omap->pdata->set_pwm(omap->dm_timer,
> +			     pwm_get_polarity(pwm) == PWM_POLARITY_INVERSED,
> +			     true, OMAP_TIMER_TRIGGER_OVERFLOW_AND_COMPARE,
> +			     false);
> +
>  	mutex_unlock(&omap->mutex);
>  }

I'm seeing an issue with this patch where after use something is
left on and power consumption stays higher by about 30 mW after
use.

I can reproduce this easily on droid4 with Sebastian's rumble-test
app[0]. After use, I sometimes also hear the vibrator keep chirping
quietly, so there seems to be some pwm still happening after disable :)

Reloading modules for pwm-vibra and pwm-omap-dmtimer make the power
consumption go back down again.

If you have a scope set up, maybe check the lines are quiet after
disable after this patch?

Regards,

Tony


[0] https://git.collabora.com/cgit/user/sre/rumble-test.git/plain/rumble-test.c