linux-kernel - [PATCH] pwm-regulator: Add support for a fixed delay after duty cycle changes

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Message-ID: <20160826231336.GA92391@google.com>
Date:   Fri, 26 Aug 2016 16:13:36 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>
Cc:     Doug Anderson <dianders@...omium.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] pwm-regulator: Add support for a fixed delay after duty
 cycle changes

A change of the duty cycle doesn't necessarily cause an inmediate switch
to the target voltage. The voltage change may be gradual and complete
with a certain delay. This change introduces the device tree properties
"settle-time-up-us" and "settle-time-down-us", which allow to specify a
fixed delay after a voltage increase or decrease. Often it is not
strictly necessary for a voltage decrease to complete, therefore the
delays may be asymmetric for voltage. For regulators with a ramp delay
the corresponding settle time is added to the ramp delay.

Change-Id: Ib3543a250e1dfc14964ec72bd2684237728a08a3
Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
---
 .../bindings/regulator/pwm-regulator.txt           | 10 +++++++++
 drivers/regulator/pwm-regulator.c                  | 24 ++++++++++++++++++----
 2 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/Documentation/devicetree/bindings/regulator/pwm-regulator.txt b/Documentation/devicetree/bindings/regulator/pwm-regulator.txt
index 3aeba9f..42b6819 100644
--- a/Documentation/devicetree/bindings/regulator/pwm-regulator.txt
+++ b/Documentation/devicetree/bindings/regulator/pwm-regulator.txt
@@ -29,6 +29,16 @@ Required properties:
 
 - pwms:			PWM specification (See: ../pwm/pwm.txt)
 
+Optional properties:
+--------------------
+- settle-time-up-us:	Time to settle down after a voltage increase
+			(unit: us). For regulators with a ramp delay
+			the two values are added.
+
+- settle-time-down-us:	Time to settle down after a voltage decrease
+			(unit: us). For regulators with a ramp delay
+			the two values are added.
+
 Only required for Voltage Table Mode:
 - voltage-table: 	Voltage and Duty-Cycle table consisting of 2 cells
 			    First cell is voltage in microvolts (uV)
diff --git a/drivers/regulator/pwm-regulator.c b/drivers/regulator/pwm-regulator.c
index c245242..cd7575b 100644
--- a/drivers/regulator/pwm-regulator.c
+++ b/drivers/regulator/pwm-regulator.c
@@ -46,6 +46,9 @@ struct pwm_regulator_data {
 
 	int state;
 
+	u32 settle_time_up_us;
+	u32 settle_time_down_us;
+
 	/* Enable GPIO */
 	struct gpio_desc *enb_gpio;
 };
@@ -195,6 +198,7 @@ static int pwm_regulator_set_voltage(struct regulator_dev *rdev,
 	unsigned int max_uV_duty = drvdata->continuous.max_uV_dutycycle;
 	unsigned int duty_unit = drvdata->continuous.dutycycle_unit;
 	unsigned int ramp_delay = rdev->constraints->ramp_delay;
+	unsigned int delay;
 	int min_uV = rdev->constraints->min_uV;
 	int max_uV = rdev->constraints->max_uV;
 	int diff_uV = max_uV - min_uV;
@@ -233,12 +237,19 @@ static int pwm_regulator_set_voltage(struct regulator_dev *rdev,
 		return ret;
 	}
 
-	if ((ramp_delay == 0) || !pwm_regulator_is_enabled(rdev))
+	if (req_min_uV > old_uV)
+                delay = drvdata->settle_time_up_us;
+        else
+                delay = drvdata->settle_time_down_us;
+
+	if (!pwm_regulator_is_enabled(rdev) || (delay == 0) && (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));
+	if (ramp_delay != 0)
+		/* Adjust ramp delay to uS and add to settle time. */
+		delay += DIV_ROUND_UP(abs(req_min_uV - old_uV), ramp_delay);
+
+	usleep_range(delay, delay + DIV_ROUND_UP(delay, 10));
 
 	return 0;
 }
@@ -368,6 +379,11 @@ static int pwm_regulator_probe(struct platform_device *pdev)
 	if (!init_data)
 		return -ENOMEM;
 
+	of_property_read_u32(np, "settle-time-up-us",
+			&drvdata->settle_time_up_us);
+	of_property_read_u32(np, "settle-time-down-us",
+			&drvdata->settle_time_down_us);
+
 	config.of_node = np;
 	config.dev = &pdev->dev;
 	config.driver_data = drvdata;
-- 
2.6.6