On Thu, Sep 09, 2021 at 10:05:17AM +0200, Uwe Kleine-König wrote:
Hi Uwe!
Thanks for your feedback!
> Hello,
>
> On Wed, Sep 08, 2021 at 05:59:01PM +0200, 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@xxxxxxxx>
> > ---
> >
> > v2:
> > - Move fix above setting of disabled_mask
> >
> > 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..53edc0da3ff8 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);
> > +
>
> If you move the definition of __pwm_samsung_manual_update before
> pwm_samsung_disable() you can drop this declaration:
>
Yes, I will do that. Thanks.
> diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c
> index d904a2480849..b405dd434ad6 100644
> --- a/drivers/pwm/pwm-samsung.c
> +++ b/drivers/pwm/pwm-samsung.c
> @@ -105,9 +105,6 @@ 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)
> {
> @@ -120,6 +117,32 @@ static inline unsigned int to_tcon_channel(unsigned int channel)
> return (channel == 0) ? 0 : (channel + 1);
> }
>
> +static void __pwm_samsung_manual_update(struct samsung_pwm_chip *chip,
> + struct pwm_device *pwm)
> +{
> + unsigned int tcon_chan = to_tcon_channel(pwm->hwpwm);
> + u32 tcon;
> +
> + tcon = readl(chip->base + REG_TCON);
> + tcon |= TCON_MANUALUPDATE(tcon_chan);
> + writel(tcon, chip->base + REG_TCON);
> +
> + tcon &= ~TCON_MANUALUPDATE(tcon_chan);
> + writel(tcon, chip->base + REG_TCON);
> +}
> +
> +static void pwm_samsung_manual_update(struct samsung_pwm_chip *chip,
> + struct pwm_device *pwm)
> +{
> + unsigned long flags;
> +
> + spin_lock_irqsave(&samsung_pwm_lock, flags);
> +
> + __pwm_samsung_manual_update(chip, pwm);
> +
> + spin_unlock_irqrestore(&samsung_pwm_lock, flags);
> +}
> +
> static void pwm_samsung_set_divisor(struct samsung_pwm_chip *pwm,
> unsigned int channel, u8 divisor)
> {
> @@ -291,32 +314,6 @@ static void pwm_samsung_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> spin_unlock_irqrestore(&samsung_pwm_lock, flags);
> }
>
> -static void __pwm_samsung_manual_update(struct samsung_pwm_chip *chip,
> - struct pwm_device *pwm)
> -{
> - unsigned int tcon_chan = to_tcon_channel(pwm->hwpwm);
> - u32 tcon;
> -
> - tcon = readl(chip->base + REG_TCON);
> - tcon |= TCON_MANUALUPDATE(tcon_chan);
> - writel(tcon, chip->base + REG_TCON);
> -
> - tcon &= ~TCON_MANUALUPDATE(tcon_chan);
> - writel(tcon, chip->base + REG_TCON);
> -}
> -
> -static void pwm_samsung_manual_update(struct samsung_pwm_chip *chip,
> - struct pwm_device *pwm)
> -{
> - unsigned long flags;
> -
> - spin_lock_irqsave(&samsung_pwm_lock, flags);
> -
> - __pwm_samsung_manual_update(chip, pwm);
> -
> - spin_unlock_irqrestore(&samsung_pwm_lock, flags);
> -}
> -
> static int __pwm_samsung_config(struct pwm_chip *chip, struct pwm_device *pwm,
> int duty_ns, int period_ns, bool force_period)
> {
>
> )
>
> Maybe split the patch to have it nice and reviewable?
If I only move up the definition of __pwm_samsung_manual_update, and
leave pwm_samsung_manual_update at its place, the patch becomes quite
straightforward and overviewable. Or do you prefer to group the definitions
of those two functions together?
Kind regards
Mårten
>
> Orthogonal to your patch: I wonder what &samsung_pwm_lock actually
> protects and why it disables irqs. In general the pwm functions might
> sleep, at least some implementations do.
>
> Best regards
> Uwe
>
> --
> Pengutronix e.K. | Uwe Kleine-König |
> Industrial Linux Solutions | https://www.pengutronix.de/ |
