From: Marten Lindahl <martenli@axis.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Cc: "Mårten Lindahl" <Marten.Lindahl@axis.com>,
"Thierry Reding" <thierry.reding@gmail.com>,
"Lee Jones" <lee.jones@linaro.org>,
"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-samsung-soc@vger.kernel.org"
<linux-samsung-soc@vger.kernel.org>,
"linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>,
kernel <kernel@axis.com>
Subject: Re: [PATCH] pwm: pwm-samsung: Trigger manual update when disabling PWM
Date: Wed, 8 Sep 2021 17:50:58 +0200 [thread overview]
Message-ID: <20210908155058.GA3587@axis.com> (raw)
In-Reply-To: <fc40e31d-16a2-33f3-1eb0-4af81fc27065@canonical.com>
On Wed, Sep 08, 2021 at 04:54:04PM +0200, Krzysztof Kozlowski wrote:
> On 08/09/2021 16:27, Mårten Lindahl wrote:
> > When duty-cycle is at full level (100%), the TCNTn and TCMPn registers
> > needs to be flushed in order to disable the signal. The PWM manual does
> > not say anything about this, but states that only clearing the TCON
> > auto-reload bit should be needed, and this seems to be true when the PWM
> > duty-cycle is not at full level. This can be observed on an Axis
> > ARTPEC-8, by running:
> >
> > echo <period> > pwm/period
> > echo <period> > pwm/duty_cycle
> > echo 1 > pwm/enable
> > echo 0 > pwm/enable
> >
> > Since the TCNTn and TCMPn registers are activated when enabling the PWM
> > (setting TCON auto-reload bit), and are not touched when disabling the
> > PWM, the double buffered auto-reload function seems to be still active.
> > Lowering duty-cycle, and restoring it again in between the enabling and
> > disabling, makes the disable work since it triggers a reload of the
> > TCNTn and TCMPn registers.
> >
> > Fix this by securing a reload of the TCNTn and TCMPn registers when
> > disabling the PWM and having a full duty-cycle.
> >
> > Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
> > ---
> > drivers/pwm/pwm-samsung.c | 25 +++++++++++++++++++++----
> > 1 file changed, 21 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c
> > index f6c528f02d43..7d90652402a0 100644
> > --- a/drivers/pwm/pwm-samsung.c
> > +++ b/drivers/pwm/pwm-samsung.c
> > @@ -105,6 +105,9 @@ struct samsung_pwm_chip {
> > static DEFINE_SPINLOCK(samsung_pwm_lock);
> > #endif
> >
> > +static void __pwm_samsung_manual_update(struct samsung_pwm_chip *chip,
> > + struct pwm_device *pwm);
> > +
> > static inline
> > struct samsung_pwm_chip *to_samsung_pwm_chip(struct pwm_chip *chip)
> > {
> > @@ -278,17 +281,21 @@ static void pwm_samsung_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> >
> > our_chip->disabled_mask |= BIT(pwm->hwpwm);
> >
> > + /*
> > + * In case the PWM is at 100% duty cycle, force a manual
> > + * update to prevent the signal from staying high.
> > + */
> > + if (readl(our_chip->base + REG_TCMPB(pwm->hwpwm)) == (u32)-1U)
> > + __pwm_samsung_manual_update(our_chip, pwm);
>
> I did not test it but looks reasonable. Just please move it above
> setting "our_chip->disabled_mask", so the code will be close to
> pwm_samsung_enable.
>
Hi Krzysztof!
Thank you for the quick reply! I will do so.
Kind regards
Mårten
>
> Best regards,
> Krzysztof
prev parent reply other threads:[~2021-09-08 15:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-08 14:27 [PATCH] pwm: pwm-samsung: Trigger manual update when disabling PWM Mårten Lindahl
2021-09-08 14:54 ` Krzysztof Kozlowski
2021-09-08 15:50 ` Marten Lindahl [this message]
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