[PATCH] pwm: Add clk enable/disable for pwm_samsung_enable/pwm_samsung_disable

[PATCH] pwm: Add clk enable/disable for pwm_samsung_enable/pwm_samsung_disable

[Anand Moon]

It's safe to disable the clk when we following.
	pwm_config(pwm, 0, period);
 	pwm_disable(pwm);
And enable clk when we do following.
	pwm_config(pwm, duty, period);
 	pwm_enable(pwm);

Tested on OdroidXU3 Board.

Signed-off-by: Anand Moon <linux.amoon@gmail.com>
---
 drivers/pwm/pwm-samsung.c | 2 ++
 1 file changed, 2 insertions(+)

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);
 }
-- 
1.9.1

Re: [PATCH] pwm: Add clk enable/disable for pwm_samsung_enable/pwm_samsung_disable

[Sjoerd Simons]

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.

Re: [PATCH] pwm: Add clk enable/disable for pwm_samsung_enable/pwm_samsung_disable

[Anand Moon]

hi Sjoerd,

Are you referring to handle of polarity
(PWM_POLARITY_NORMAL/PWM_POLARITY_INVERSED) during enable and disable.

How can I analyses if the clock is high and low.

-Anand Moon

On 15 April 2015 at 14:04, Sjoerd Simons <sjoerd.simons@collabora.co.uk> wrote:
> 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.