leds: leds-lp50xx: Enable chip before any communication

If a GPIO is used to control the chip's enable pin, it needs to be pulled
high before any i2c communication is attempted.

Currently, the enable GPIO handling is not correct.

Assume the enable GPIO is low when the probe function is entered. In this
case the device is in SHUTDOWN mode and does not react to i2c commands.

During probe the following sequence happens:
1. The call to lp50xx_reset() on line 548 has no effect as i2c is not
possible yet.
2. Then - on line 552 - lp50xx_enable_disable() is called. As
"priv->enable_gpio“ has not yet been initialized, setting the GPIO has
no effect. Also the i2c enable command is not executed as the device
is still in SHUTDOWN.
3. On line 556 the call to lp50xx_probe_dt() finally parses the rest of
the DT and the configured priv->enable_gpio is set up.

As a result the device is still in SHUTDOWN mode and not ready for
operation.

Split lp50xx_enable_disable() into distinct enable and disable functions
to enforce correct ordering between enable_gpio manipulations and i2c
commands.
Read enable_gpio configuration from DT before attempting to manipulate
enable_gpio.
Add delays to observe correct wait timing after manipulating enable_gpio
and before any i2c communication.

Cc: [e-mail]
Fixes: 242b81170fb8 ("leds: lp50xx: Add the LP50XX family of the RGB LED driver")
Signed-off-by: Christian Hitz <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/leds/leds-lp50xx.c

···
 
 #define LP50XX_SW_RESET		0xff
 #define LP50XX_CHIP_EN		BIT(6)
+#define LP50XX_CHIP_DISABLE	0x00
+#define LP50XX_START_TIME_US	500
+#define LP50XX_RESET_TIME_US	3
+
+#define LP50XX_EN_GPIO_LOW	0
+#define LP50XX_EN_GPIO_HIGH	1
 
 /* There are 3 LED outputs per bank */
 #define LP50XX_LEDS_PER_MODULE	3
···
 	return regmap_write(priv->regmap, priv->chip_info->reset_reg, LP50XX_SW_RESET);
 }
 
-static int lp50xx_enable_disable(struct lp50xx *priv, int enable_disable)
+static int lp50xx_enable(struct lp50xx *priv)
 {
 	int ret;
 
-	ret = gpiod_direction_output(priv->enable_gpio, enable_disable);
+	if (priv->enable_gpio) {
+		ret = gpiod_direction_output(priv->enable_gpio, LP50XX_EN_GPIO_HIGH);
+		if (ret)
+			return ret;
+
+		udelay(LP50XX_START_TIME_US);
+	}
+
+	ret = lp50xx_reset(priv);
 	if (ret)
 		return ret;
 
-	if (enable_disable)
-		return regmap_write(priv->regmap, LP50XX_DEV_CFG0, LP50XX_CHIP_EN);
-	else
-		return regmap_write(priv->regmap, LP50XX_DEV_CFG0, 0);
+	return regmap_write(priv->regmap, LP50XX_DEV_CFG0, LP50XX_CHIP_EN);
+}
 
+static int lp50xx_disable(struct lp50xx *priv)
+{
+	int ret;
+
+	ret = regmap_write(priv->regmap, LP50XX_DEV_CFG0, LP50XX_CHIP_DISABLE);
+	if (ret)
+		return ret;
+
+	if (priv->enable_gpio) {
+		ret = gpiod_direction_output(priv->enable_gpio, LP50XX_EN_GPIO_LOW);
+		if (ret)
+			return ret;
+
+		udelay(LP50XX_RESET_TIME_US);
+	}
+
+	return 0;
 }
 
 static int lp50xx_probe_leds(struct fwnode_handle *child, struct lp50xx *priv,
···
 	if (IS_ERR(priv->enable_gpio))
 		return dev_err_probe(priv->dev, PTR_ERR(priv->enable_gpio),
 				     "Failed to get enable GPIO\n");
+
+	ret = lp50xx_enable(priv);
+	if (ret)
+		return ret;
 
 	priv->regulator = devm_regulator_get(priv->dev, "vled");
 	if (IS_ERR(priv->regulator))
···
 		return ret;
 	}
 
-	ret = lp50xx_reset(led);
-	if (ret)
-		return ret;
-
-	ret = lp50xx_enable_disable(led, 1);
-	if (ret)
-		return ret;
-
 	return lp50xx_probe_dt(led);
 }
 
···
 	struct lp50xx *led = i2c_get_clientdata(client);
 	int ret;
 
-	ret = lp50xx_enable_disable(led, 0);
+	ret = lp50xx_disable(led);
 	if (ret)
 		dev_err(led->dev, "Failed to disable chip\n");