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.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/sbs-battery.c

@@ -51,6 +51,14 @@ enum {
 	REG_CHARGE_VOLTAGE,
 };
 
+#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
+
 #define REG_ADDR_MANUFACTURE_DATE	0x1B
 
 /* Battery Mode defines */
@@ -224,14 +232,57 @@ exit:
 
 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");
+
 	if (!chip->is_present && is_present && !chip->charger_broadcasts)
 		sbs_disable_charger_broadcasts(chip);
 
@@ -273,7 +324,8 @@ static int sbs_read_string_data_fallback(struct i2c_client *client, u8 address,
 	retries_length = chip->i2c_retry_count;
 	retries_block = chip->i2c_retry_count;
 
-	dev_warn_once(&client->dev, "I2C adapter does not support I2C_FUNC_SMBUS_READ_BLOCK_DATA.\n");
+	dev_warn_once(&client->dev, "I2C adapter does not support I2C_FUNC_SMBUS_READ_BLOCK_DATA.\n"
+				    "Fallback method does not support PEC.\n");
 
 	/* Adapter needs to support these two functions */
 	if (!i2c_check_functionality(client->adapter,
@@ -336,8 +388,14 @@ static int sbs_read_string_data(struct i2c_client *client, u8 address, char *val
 	int retries = chip->i2c_retry_count;
 	int ret = 0;
 
-	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_BLOCK_DATA))
-		return sbs_read_string_data_fallback(client, address, values);
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_BLOCK_DATA)) {
+		bool pec = client->flags & I2C_CLIENT_PEC;
+		client->flags &= ~I2C_CLIENT_PEC;
+		ret = sbs_read_string_data_fallback(client, address, values);
+		if (pec)
+			client->flags |= I2C_CLIENT_PEC;
+		return ret;
+	}
 
 	while (retries > 0) {
 		ret = i2c_smbus_read_block_data(client, address, values);