leds: lm3601x: Calculate max_brightness and brightness properly

The torch_current_max should be checked not exceeding the upper bound.
If it does, throw a warning message and set to LM3601X_MAX_TORCH_I_UA.

LM3601x torch brigthness register (LM3601X_LED_TORCH_REG) takes 0 as the
minimum output (2.4 mA). However, 0 of led_brightness means LED_OFF.
Adding a -1 offset to brightness before writing to brightness
register, so when users write minimum brightness (1), it sets lm3601x
output the minimum.
Signed-off-by: Jack Chen <zenghuchen@google.com>
Link: https://lore.kernel.org/r/20240704191500.766846-1-zenghuchen@google.comSigned-off-by: Lee Jones <lee@kernel.org>

drivers/leds/flash/leds-lm3601x.c

@@ -190,7 +190,7 @@ static int lm3601x_brightness_set(struct led_classdev *cdev,
 		goto out;
 	}
 
-	ret = regmap_write(led->regmap, LM3601X_LED_TORCH_REG, brightness);
+	ret = regmap_write(led->regmap, LM3601X_LED_TORCH_REG, brightness - 1);
 	if (ret < 0)
 		goto out;
 
@@ -341,8 +341,9 @@ static int lm3601x_register_leds(struct lm3601x_led *led,
 
 	led_cdev = &led->fled_cdev.led_cdev;
 	led_cdev->brightness_set_blocking = lm3601x_brightness_set;
-	led_cdev->max_brightness = DIV_ROUND_UP(led->torch_current_max,
-						LM3601X_TORCH_REG_DIV);
+	led_cdev->max_brightness =
+			DIV_ROUND_UP(led->torch_current_max - LM3601X_MIN_TORCH_I_UA + 1,
+				     LM3601X_TORCH_REG_DIV);
 	led_cdev->flags |= LED_DEV_CAP_FLASH;
 
 	init_data.fwnode = fwnode;
@@ -386,6 +387,14 @@ static int lm3601x_parse_node(struct lm3601x_led *led,
 		goto out_err;
 	}
 
+	if (led->torch_current_max > LM3601X_MAX_TORCH_I_UA) {
+		dev_warn(&led->client->dev,
+			 "Max torch current set too high (%d vs %d)\n",
+			 led->torch_current_max,
+			 LM3601X_MAX_TORCH_I_UA);
+		led->torch_current_max = LM3601X_MAX_TORCH_I_UA;
+	}
+
 	ret = fwnode_property_read_u32(child, "flash-max-microamp",
 				&led->flash_current_max);
 	if (ret) {