backlight: rt4831: Apply ocp level from devicetree

Add 'richtek,bled-ocp-microamp' property parsing in
device_property_init function.

This value may configure prior to the kernel driver. If it's not specified in
devicetree, keep the original setting. Else, use clamp to align the
value in min/max range and also roundup to choose the best selector.

Reported-by: Lucas Tsai <[e-mail]>
Signed-off-by: ChiYuan Huang <[e-mail]>
Reviewed-by: Daniel Thompson <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/video/backlight/rt4831-backlight.c

···
 #define RT4831_REG_BLCFG	0x02
 #define RT4831_REG_BLDIML	0x04
 #define RT4831_REG_ENABLE	0x08
+#define RT4831_REG_BLOPT2	0x11
 
 #define RT4831_BLMAX_BRIGHTNESS	2048
 
···
 #define RT4831_BLDIML_MASK	GENMASK(2, 0)
 #define RT4831_BLDIMH_MASK	GENMASK(10, 3)
 #define RT4831_BLDIMH_SHIFT	3
+#define RT4831_BLOCP_MASK	GENMASK(1, 0)
+
+#define RT4831_BLOCP_MINUA	900000
+#define RT4831_BLOCP_MAXUA	1800000
+#define RT4831_BLOCP_STEPUA	300000
 
 struct rt4831_priv {
 	struct device *dev;
···
 {
 	struct device *dev = priv->dev;
 	u8 propval;
-	u32 brightness;
+	u32 brightness, ocp_uA;
 	unsigned int val = 0;
 	int ret;
 
···
 				 propval << RT4831_BLOVP_SHIFT);
 	if (ret)
 		return ret;
+
+	/*
+	 * This OCP level is used to protect and limit the inductor current.
+	 * If inductor peak current reach the level, low-side MOSFET will be
+	 * turned off. Meanwhile, the output channel current may be limited.
+	 * To match the configured channel current, the inductor chosen must
+	 * be higher than the OCP level.
+	 *
+	 * Not like the OVP level, the default 21V can be used in the most
+	 * application. But if the chosen OCP level is smaller than needed,
+	 * it will also affect the backlight channel output current to be
+	 * smaller than the register setting.
+	 */
+	ret = device_property_read_u32(dev, "richtek,bled-ocp-microamp",
+				       &ocp_uA);
+	if (!ret) {
+		ocp_uA = clamp_val(ocp_uA, RT4831_BLOCP_MINUA,
+				   RT4831_BLOCP_MAXUA);
+		val = DIV_ROUND_UP(ocp_uA - RT4831_BLOCP_MINUA,
+				   RT4831_BLOCP_STEPUA);
+		ret = regmap_update_bits(priv->regmap, RT4831_REG_BLOPT2,
+					 RT4831_BLOCP_MASK, val);
+		if (ret)
+			return ret;
+	}
 
 	ret = device_property_read_u8(dev, "richtek,channel-use", &propval);
 	if (ret) {