linux-kernel - Re: [PATCH v9 12/27] pwm: jz4740: Use regmap from TCU driver

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Date:   Sat, 5 Jan 2019 22:18:20 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Jonathan Corbet <corbet@....net>, linux-pwm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-watchdog@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH v9 12/27] pwm: jz4740: Use regmap from TCU driver

Hello Paul,

On Sat, Jan 05, 2019 at 05:46:18PM -0300, Paul Cercueil wrote:
> On Sat, Jan 5, 2019 at 4:42 PM, Uwe Kleine-König
> <u.kleine-koenig@...gutronix.de> wrote:
> > On Thu, Dec 27, 2018 at 07:13:04PM +0100, Paul Cercueil wrote:
> > >  The ingenic-timer "TCU" driver provides us with a regmap, that we
> > > can
> > >  use to safely access the TCU registers.
> > > 
> > >  While this driver is devicetree-compatible, it is never (as of now)
> > >  probed from devicetree, so this change does not introduce a ABI
> > > problem
> > >  with current devicetree files.
> > 
> > Does it change behaviour? If so, how?
> 
> No, it does not change the behaviour.

Then this paragraph in the commit log can better be dropped.

> > >  @@ -113,26 +117,37 @@ static int jz4740_pwm_apply(struct pwm_chip
> > > *chip, struct pwm_device *pwm,
> > > 
> > >   	jz4740_pwm_disable(chip, pwm);
> > > 
> > >  -	jz4740_timer_set_count(pwm->hwpwm, 0);
> > >  -	jz4740_timer_set_duty(pwm->hwpwm, duty);
> > >  -	jz4740_timer_set_period(pwm->hwpwm, period);
> > >  +	/* Set abrupt shutdown */
> > >  +	regmap_update_bits(jz4740->map, TCU_REG_TCSRc(pwm->hwpwm),
> > >  +			   TCU_TCSR_PWM_SD, TCU_TCSR_PWM_SD);
> > 
> > I think I already pointed that out before: abrupt mode is wrong. If
> > .apply is called with a new set of parameters the currently running
> > period with the old values is expected to complete before the new values
> > take effect.
> 
> You pointed it, indeed; but I won't change it until I can verify that the
> behaviour is correct (which does not seem to be the case even if I leave
> this bit cleared). Besides, this is the TCU patchset, fixes and patches
> unrelated to the TCU don't belong here.

So abrupt mode was already used before? Then maybe note in a comment
that this is wrong but kept for now as this change is only refactoring
without changing behaviour.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |