linux-kernel - Re: [PATCH] regulator: pwm: Fix regulator ramp delay for continuous mode

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Date:	Wed, 6 Jul 2016 14:27:19 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Douglas Anderson <dianders@...omium.org>
Cc:	Mark Brown <broonie@...nel.org>, lee.jones@...aro.org,
	briannorris@...omium.org, linux-rockchip@...ts.infradead.org,
	Heiko Stuebner <heiko@...ech.de>, lgirdwood@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] regulator: pwm: Fix regulator ramp delay for continuous
 mode

On Mon, 27 Jun 2016 21:53:11 -0700
Douglas Anderson <dianders@...omium.org> wrote:

> The original commit adding support for continuous voltage mode didn't
> handle the regulator ramp delay properly.  It treated the delay as a
> fixed delay in uS despite the property being defined as uV / uS.  Let's
> adjust it.  Luckily there appear to be no users of this ramp delay for
> PWM regulators (as per grepping through device trees in linuxnext).
> 
> Note also that the upper bound of usleep_range probably shouldn't be a
> full 1 ms longer than the lower bound since I've seen plenty of hardware
> with a ramp rate of ~5000 uS / uV and for small jumps the total delays
> are in the tens of uS.  1000 is way too much.  We'll try to be dynamic
> and use 10%

I realize I may have introduced another bug when adding the
->enable()/disable() methods: we are only waiting for the ramp up delay
when changing the voltage, but it should probably be applied when
enabling the PWM, and conditionally applied when changing the voltage
only if the PWM is enabled.

> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> Note that this patch is atop Boris's recent PWM regulator fixes.  If
> desired it wouldn't be too hard to write it atop the old code, though
> quite honestly anyone using a PWM regulator should probably be using his
> new code.
> 
>  drivers/regulator/pwm-regulator.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/regulator/pwm-regulator.c b/drivers/regulator/pwm-regulator.c
> index fa1c74c77bb0..de94d19f6e1f 100644
> --- a/drivers/regulator/pwm-regulator.c
> +++ b/drivers/regulator/pwm-regulator.c
> @@ -188,6 +188,7 @@ static int pwm_regulator_set_voltage(struct regulator_dev *rdev,
>  	struct pwm_state pstate;
>  	unsigned int diff_duty;
>  	unsigned int dutycycle;
> +	int old_uV = pwm_regulator_get_voltage(rdev);
>  	int ret;
>  
>  	pwm_init_state(drvdata->pwm, &pstate);
> @@ -219,8 +220,12 @@ static int pwm_regulator_set_voltage(struct regulator_dev *rdev,
>  		return ret;
>  	}
>  
> -	/* Delay required by PWM regulator to settle to the new voltage */
> -	usleep_range(ramp_delay, ramp_delay + 1000);
> +	if (ramp_delay == 0)
> +		return 0;
> +
> +	/* Ramp delay is in uV/uS. Adjust to uS and delay */
> +	ramp_delay = DIV_ROUND_UP(abs(req_min_uV - old_uV), ramp_delay);
> +	usleep_range(ramp_delay, ramp_delay + DIV_ROUND_UP(ramp_delay, 10));
>  
>  	return 0;
>  }