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SubjectRe: [PATCH] pwm: Add clk enable/disable for pwm_samsung_enable/pwm_samsung_disable
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On Wed, 2015-04-15 at 03:35 +0930, Anand Moon wrote:
> diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c
> index 3e9b583..b579753 100644
> --- a/drivers/pwm/pwm-samsung.c
> +++ b/drivers/pwm/pwm-samsung.c
> @@ -247,6 +247,7 @@ static int pwm_samsung_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> tcon &= ~TCON_MANUALUPDATE(tcon_chan);
> tcon |= TCON_START(tcon_chan) | TCON_AUTORELOAD(tcon_chan);
> writel(tcon, our_chip->base + REG_TCON);
> + clk_prepare_enable(our_chip->base_clk);
>
> spin_unlock_irqrestore(&samsung_pwm_lock, flags);
>
> @@ -265,6 +266,7 @@ static void pwm_samsung_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> tcon = readl(our_chip->base + REG_TCON);
> tcon &= ~TCON_AUTORELOAD(tcon_chan);
> writel(tcon, our_chip->base + REG_TCON);
> + clk_disable_unprepare(our_chip->base_clk);
>
> spin_unlock_irqrestore(&samsung_pwm_lock, flags);
> }

As far as i can tell this code doesn't have any effect.

clk_enable is refcounted, so the clock will stay enabled for as long as
the driver is loaded (as it's enabled in _probe). Your code above just
raises and lowers the clocks enabled refcount, but won't actually ever
cause it to be disabled.

With respect to trying to disabling the clocks on pwm_disable, that will
need some more work to ensure the output signal has the expected level
when you turn of the clock. Specifically, when disabling from a non-100%
duty state the driver relies on the PWM turning the output signal low at
the end of a duty cycle. However if you turn off the clock at the start
of a duty cycle while the output signal is still high it will
unexpectedly remain high.


--
Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Collabora Ltd.


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