From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: "Clément Péron" <peron.clem@gmail.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
Florian Fainelli <f.fainelli@gmail.com>,
Ray Jui <rjui@broadcom.com>,
Scott Branden <sbranden@broadcom.com>,
bcm-kernel-feedback-list@broadcom.com, linux-pwm@vger.kernel.org,
linux-kernel@vger.kernel.org,
Suji Velupillai <suji.velupillai@broadcom.com>,
Tim Kryger <tim.kryger@linaro.org>
Subject: Re: [PATCH 2/2] pwm: bcm-kona: apply pwm settings on enable
Date: Thu, 8 Nov 2018 11:59:22 +0100 [thread overview]
Message-ID: <20181108105922.p557jxrebjlhnsho@pengutronix.de> (raw)
In-Reply-To: <CAJiuCccMtBsCVHeqxQhXRj_Ltdv91Qk-6WDKAhb5S7whZOWsAw@mail.gmail.com>
Hello,
adding Tim Kryger as the initial author of the bcm-kona driver to Cc:.
Maybe he can shed some light to the questions below?
On Thu, Nov 08, 2018 at 11:47:17AM +0100, Clément Péron wrote:
> On Wed, 7 Nov 2018 at 17:29, Uwe Kleine-König
> <u.kleine-koenig@pengutronix.de> wrote:
> > On Wed, Nov 07, 2018 at 10:36:13AM +0100, Clément Péron wrote:
> > > From: Suji Velupillai <suji.velupillai@broadcom.com>
> > >
> > > When pwm_bl framework calls enable, a call to pwm_is_enabled(pwm) still
> > > return false, this prevents the backlight being turn on at boot time.
> > >
> > > Signed-off-by: Suji Velupillai <suji.velupillai@broadcom.com>
> > > Signed-off-by: Clément Péron <peron.clem@gmail.com>
> > > ---
> > > drivers/pwm/pwm-bcm-kona.c | 16 +++++++++++-----
> > > 1 file changed, 11 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/pwm/pwm-bcm-kona.c b/drivers/pwm/pwm-bcm-kona.c
> > > index 09a95aeb3a70..d991d53c4b38 100644
> > > --- a/drivers/pwm/pwm-bcm-kona.c
> > > +++ b/drivers/pwm/pwm-bcm-kona.c
> > > @@ -108,8 +108,8 @@ static void kona_pwmc_apply_settings(struct kona_pwmc *kp, unsigned int chan)
> > > ndelay(400);
> > > }
> > >
> > > -static int kona_pwmc_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > > - int duty_ns, int period_ns)
> > > +static int __pwmc_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > > + int duty_ns, int period_ns, bool pwmc_enabled)
> > > {
> > > struct kona_pwmc *kp = to_kona_pwmc(chip);
> > > u64 val, div, rate;
> > > @@ -155,7 +155,7 @@ static int kona_pwmc_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > > * always calculated above to ensure the new values are
> > > * validated immediately instead of on enable.
> > > */
> > > - if (pwm_is_enabled(pwm)) {
> > > + if (pwm_is_enabled(pwm) || pwmc_enabled) {
> >
> > Having pwm-API-calls in hw-drivers is ugly. Apart from not giving the
> > intended return code this function should IMHO be reserved to pwm
> > consumers. The underlaying problem is that pwm-bl does:
> >
> > pwm_config(pwm, duty_cycle, period);
> > pwm_enable(pwm);
> >
> > and expects that the duty_cycle and period is used then. Doesn't
> > everything works just fine if the if-block is always executed?
>
> Tested and works fine for me. But I only have a Cygnus proc.
> Maybe there is some issue with Kona as explained by the comment (even
> if I don't understand it well).
>
> * Don't apply settings if disabled. The period and duty cycle are
> * always calculated above to ensure the new values are
> * validated immediately instead of on enable.
I wouldn't understand that as "If you apply settings on a disabled PWM a
kitten dies". I think it only means: At the current point in time
duty_cycle and period are not important as the hardware is off. So don't
bother to write these values to the hardware.
@Tim: Do you think (or can test if) there is a problem when doing
- if (pwm_is_enabled(pwm)) {
+ if (1) {
in kona_pwmc_config? (For sure the comment needs adaption and the if (1)
shouldn't make it into the driver, just used that as shorthand for the
change I want to suggest.)
But still better than dropping the check is to convert the driver to the
atomic API. With that this problem would simply not occur.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
next prev parent reply other threads:[~2018-11-08 10:59 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-07 9:36 [PATCH 1/2] pwm: kconfig: enable kona pwm to be built for cygnus arch Clément Péron
2018-11-07 9:36 ` [PATCH 2/2] pwm: bcm-kona: apply pwm settings on enable Clément Péron
2018-11-07 16:29 ` Uwe Kleine-König
2018-11-08 10:47 ` Clément Péron
2018-11-08 10:59 ` Uwe Kleine-König [this message]
2018-11-08 15:32 ` Tim Kryger
2018-12-12 11:04 ` Thierry Reding
2018-12-12 11:07 ` Clément Péron
2018-11-07 16:12 ` [PATCH 1/2] pwm: kconfig: enable kona pwm to be built for cygnus arch Uwe Kleine-König
2018-11-07 16:48 ` Scott Branden
2018-11-08 10:47 ` Clément Péron
2018-11-08 12:22 ` Thierry Reding
2018-11-09 9:58 ` Clément Péron
2018-11-09 10:53 ` Uwe Kleine-König
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