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

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Date:   Mon, 9 Mar 2020 11:01:23 -0700
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> [200309 04:53]:
> Hi Tony,
> 
> On 06/03/20 11:44 PM, Tony Lindgren wrote:
> > * 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.
> 
> Interesting...What is the PWM period and duty cycle in the test case?
> Can you dump the following registers before and after disabling:
> - TLDR
> - TMAR
> - TCLR

Here's the state dumped before and after in omap_dm_timer_set_pwm():

omap_timer 4803e000.timer: XXX set_pwm before: tldr: fffffeb8 tmar: fffffffe tclr: 00000040
omap_timer 4803e000.timer: XXX set_pwm after: tldr: fffffeb8 tmar: fffffffe tclr: 00001842
omap_timer 4013e000.timer: XXX set_pwm before: tldr: fffffeb8 tmar: fffffffe tclr: 00000040
omap_timer 4013e000.timer: XXX set_pwm after: tldr: fffffeb8 tmar: fffffffe tclr: 00001842
omap_timer 4013e000.timer: XXX set_pwm before: tldr: fffffeb8 tmar: fffffffe tclr: 00001843
omap_timer 4013e000.timer: XXX set_pwm after: tldr: fffffeb8 tmar: fffffffe tclr: 00001841
omap_timer 4803e000.timer: XXX set_pwm before: tldr: fffffeb8 tmar: fffffffe tclr: 00001843
omap_timer 4803e000.timer: XXX set_pwm after: tldr: fffffeb8 tmar: fffffffe tclr: 00001841

So looks like the start bit is still enabled after use?

I think the duty cycle depends on the strength set for rumble-test.c.

> > 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 :)
> 
> hmm..The line clearly goes down on the scope after the current pwm duty cycle is
> done and never comes back.

OK

Regards,

Tony