linux-kernel - [PATCH 2/5] pwm: pca9685: Use bulk write to atomicially update registers

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Message-ID:  <bfa8c0267c9ec059d0d77f146998d564654c75ca.1753784092.git.u.kleine-koenig@baylibre.com>
Date: Tue, 29 Jul 2025 12:36:01 +0200
From: Uwe Kleine-König <u.kleine-koenig@...libre.com>
To: linux-pwm@...r.kernel.org
Cc: David Jander <david@...tonic.nl>,
	Clemens Gruber <clemens.gruber@...ruber.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] pwm: pca9685: Use bulk write to atomicially update registers

The output of a PWM channel is configured by four register values. Write
them in a single i2c transaction to ensure glitch free updates.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...libre.com>
---
 drivers/pwm/pwm-pca9685.c | 46 ++++++++++++++++++++++++---------------
 1 file changed, 29 insertions(+), 17 deletions(-)

diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
index 41eb8e034828..75cf10f2b269 100644
--- a/drivers/pwm/pwm-pca9685.c
+++ b/drivers/pwm/pwm-pca9685.c
@@ -61,6 +61,8 @@
 #define MODE1_SUB2		BIT(2)
 #define MODE1_SUB1		BIT(3)
 #define MODE1_SLEEP		BIT(4)
+#define MODE1_AI		BIT(5)
+
 #define MODE2_INVRT		BIT(4)
 #define MODE2_OUTDRV		BIT(2)
 
@@ -131,6 +133,19 @@ static int pca9685_write_reg(struct pwm_chip *chip, unsigned int reg, unsigned i
 	return err;
 }
 
+static int pca9685_write_4reg(struct pwm_chip *chip, unsigned int reg, u8 val[4])
+{
+	struct pca9685 *pca = to_pca(chip);
+	struct device *dev = pwmchip_parent(chip);
+	int err;
+
+	err = regmap_bulk_write(pca->regmap, reg, val, 4);
+	if (err)
+		dev_err(dev, "regmap_write to register 0x%x failed: %pe\n", reg, ERR_PTR(err));
+
+	return err;
+}
+
 /* Helper function to set the duty cycle ratio to duty/4096 (e.g. duty=2048 -> 50%) */
 static void pca9685_pwm_set_duty(struct pwm_chip *chip, int channel, unsigned int duty)
 {
@@ -143,12 +158,10 @@ static void pca9685_pwm_set_duty(struct pwm_chip *chip, int channel, unsigned in
 		return;
 	} else if (duty >= PCA9685_COUNTER_RANGE) {
 		/* Set the full ON bit and clear the full OFF bit */
-		pca9685_write_reg(chip, REG_ON_H(channel), LED_FULL);
-		pca9685_write_reg(chip, REG_OFF_H(channel), 0);
+		pca9685_write_4reg(chip, REG_ON_L(channel), (u8[4]){ 0, LED_FULL, 0, 0 });
 		return;
 	}
 
-
 	if (pwm->state.usage_power && channel < PCA9685_MAXCHAN) {
 		/*
 		 * If usage_power is set, the pca9685 driver will phase shift
@@ -163,12 +176,9 @@ static void pca9685_pwm_set_duty(struct pwm_chip *chip, int channel, unsigned in
 
 	off = (on + duty) % PCA9685_COUNTER_RANGE;
 
-	/* Set ON time (clears full ON bit) */
-	pca9685_write_reg(chip, REG_ON_L(channel), on & 0xff);
-	pca9685_write_reg(chip, REG_ON_H(channel), (on >> 8) & 0xf);
-	/* Set OFF time (clears full OFF bit) */
-	pca9685_write_reg(chip, REG_OFF_L(channel), off & 0xff);
-	pca9685_write_reg(chip, REG_OFF_H(channel), (off >> 8) & 0xf);
+	/* implicitly clear full ON and full OFF bit */
+	pca9685_write_4reg(chip, REG_ON_L(channel),
+			   (u8[4]){ on & 0xff, (on >> 8) & 0xf, off & 0xff, (off >> 8) & 0xf });
 }
 
 static unsigned int pca9685_pwm_get_duty(struct pwm_chip *chip, int channel)
@@ -543,9 +553,8 @@ static int pca9685_pwm_probe(struct i2c_client *client)
 
 	mutex_init(&pca->lock);
 
-	ret = pca9685_read_reg(chip, PCA9685_MODE2, &reg);
-	if (ret)
-		return ret;
+	/* clear MODE2_OCH */
+	reg = 0;
 
 	if (device_property_read_bool(&client->dev, "invert"))
 		reg |= MODE2_INVRT;
@@ -561,16 +570,19 @@ static int pca9685_pwm_probe(struct i2c_client *client)
 	if (ret)
 		return ret;
 
-	/* Disable all LED ALLCALL and SUBx addresses to avoid bus collisions */
+	/*
+	 * Disable all LED ALLCALL and SUBx addresses to avoid bus collisions,
+	 * enable Auto-Increment.
+	 */
 	pca9685_read_reg(chip, PCA9685_MODE1, &reg);
 	reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3);
+	reg |= MODE1_AI;
 	pca9685_write_reg(chip, PCA9685_MODE1, reg);
 
 	/* Reset OFF/ON registers to POR default */
-	pca9685_write_reg(chip, PCA9685_ALL_LED_OFF_L, 0);
-	pca9685_write_reg(chip, PCA9685_ALL_LED_OFF_H, LED_FULL);
-	pca9685_write_reg(chip, PCA9685_ALL_LED_ON_L, 0);
-	pca9685_write_reg(chip, PCA9685_ALL_LED_ON_H, LED_FULL);
+	ret = pca9685_write_4reg(chip, PCA9685_ALL_LED_ON_L, (u8[]){ 0, LED_FULL, 0, LED_FULL });
+	if (ret < 0)
+		return dev_err_probe(&client->dev, ret, "Failed to reset ON/OFF registers\n");
 
 	chip->ops = &pca9685_pwm_ops;
 
-- 
2.50.0