power: supply: sbs-battery: add PEC support

SBS batteries optionally have support for PEC. This enables
PEC handling based on the implemented SBS version as suggested
by the standard. The support for PEC is re-evaluated when the
battery is hotplugged into the system, since there might be
systems supporting batteries from different SBS generations.

Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/sbs-battery.c

@@ -46,6 +46,14 @@ enum {
 	REG_MODEL_NAME,
 };
 
+#define REG_ADDR_SPEC_INFO		0x1A
+#define SPEC_INFO_VERSION_MASK		GENMASK(7, 4)
+#define SPEC_INFO_VERSION_SHIFT		4
+
+#define SBS_VERSION_1_0			1
+#define SBS_VERSION_1_1			2
+#define SBS_VERSION_1_1_WITH_PEC	3
+
 /* Battery Mode defines */
 #define BATTERY_MODE_OFFSET		0x03
 #define BATTERY_MODE_CAPACITY_MASK	BIT(15)
@@ -175,6 +183,64 @@ static char model_name[I2C_SMBUS_BLOCK_MAX + 1];
 static char manufacturer[I2C_SMBUS_BLOCK_MAX + 1];
 static bool force_load;
 
+static int sbs_update_presence(struct sbs_info *chip, bool is_present)
+{
+	struct i2c_client *client = chip->client;
+	int retries = chip->i2c_retry_count;
+	s32 ret = 0;
+	u8 version;
+
+	if (chip->is_present == is_present)
+		return 0;
+
+	if (!is_present) {
+		chip->is_present = false;
+		/* Disable PEC when no device is present */
+		client->flags &= ~I2C_CLIENT_PEC;
+		return 0;
+	}
+
+	/* Check if device supports packet error checking and use it */
+	while (retries > 0) {
+		ret = i2c_smbus_read_word_data(client, REG_ADDR_SPEC_INFO);
+		if (ret >= 0)
+			break;
+
+		/*
+		 * Some batteries trigger the detection pin before the
+		 * I2C bus is properly connected. This works around the
+		 * issue.
+		 */
+		msleep(100);
+
+		retries--;
+	}
+
+	if (ret < 0) {
+		dev_dbg(&client->dev, "failed to read spec info: %d\n", ret);
+
+		/* fallback to old behaviour */
+		client->flags &= ~I2C_CLIENT_PEC;
+		chip->is_present = true;
+
+		return ret;
+	}
+
+	version = (ret & SPEC_INFO_VERSION_MASK) >> SPEC_INFO_VERSION_SHIFT;
+
+	if (version == SBS_VERSION_1_1_WITH_PEC)
+		client->flags |= I2C_CLIENT_PEC;
+	else
+		client->flags &= ~I2C_CLIENT_PEC;
+
+	dev_dbg(&client->dev, "PEC: %s\n", (client->flags & I2C_CLIENT_PEC) ?
+		"enabled" : "disabled");
+
+	chip->is_present = true;
+
+	return 0;
+}
+
 static int sbs_read_word_data(struct i2c_client *client, u8 address)
 {
 	struct sbs_info *chip = i2c_get_clientdata(client);
@@ -579,7 +645,7 @@ static int sbs_get_property(struct power_supply *psy,
 			return ret;
 		if (psp == POWER_SUPPLY_PROP_PRESENT) {
 			val->intval = ret;
-			chip->is_present = val->intval;
+			sbs_update_presence(chip, ret);
 			return 0;
 		}
 		if (ret == 0)
@@ -678,7 +744,7 @@ static int sbs_get_property(struct power_supply *psy,
 
 	if (!chip->gpio_detect &&
 		chip->is_present != (ret >= 0)) {
-		chip->is_present = (ret >= 0);
+		sbs_update_presence(chip, (ret >= 0));
 		power_supply_changed(chip->power_supply);
 	}
 
@@ -709,7 +775,7 @@ static void sbs_supply_changed(struct sbs_info *chip)
 	ret = gpiod_get_value_cansleep(chip->gpio_detect);
 	if (ret < 0)
 		return;
-	chip->is_present = ret;
+	sbs_update_presence(chip, ret);
 	power_supply_changed(battery);
 }