[PATCH v3] hwmon: (aht10) Add support for compatible aht20

[Kirill Yatsenko <kiriyatsenko@gmail.com>]

Add support for compatible AHT20 temperature/humidity sensor. The only
difference between the two is that AHT20 has additional crc8 byte.

It seems like AHT15 is also supported by the driver but it wasn't
verified and tested yet.

Tested on Beaglebone black rev C.

Signed-off-by: Kirill Yatsenko <kiriyatsenko@gmail.com>
---
v2: Add aht20 to aht10_id instead of using Kconfig flag, remove ifdefs
    as suggested by Guenter Roeck <linux@roeck-us.net>

v3: Use multi-line comments, return -EIO instead of -ENODATA, add break
    in default switch case as suggested by Guenter Roeck <linux@roeck-us.net>

 Documentation/hwmon/aht10.rst | 20 ++++++---
 drivers/hwmon/Kconfig         |  5 ++-
 drivers/hwmon/aht10.c         | 84 +++++++++++++++++++++++++++--------
 3 files changed, 83 insertions(+), 26 deletions(-)

diff --git a/Documentation/hwmon/aht10.rst b/Documentation/hwmon/aht10.rst
index 4e198c5eb683..213644b4ecba 100644
--- a/Documentation/hwmon/aht10.rst
+++ b/Documentation/hwmon/aht10.rst
@@ -5,32 +5,42 @@ Kernel driver aht10
 
 Supported chips:
 
-  * Aosong AHT10
+  * Aosong AHT10/AHT20
 
     Prefix: 'aht10'
 
     Addresses scanned: None
 
-    Datasheet:
+    Datasheet(AHT10):
 
       Chinese: http://www.aosong.com/userfiles/files/media/AHT10%E4%BA%A7%E5%93%81%E6%89%8B%E5%86%8C%20A3%2020201210.pdf
       English: https://server4.eca.ir/eshop/AHT10/Aosong_AHT10_en_draft_0c.pdf
 
+    Datasheet(AHT20):
+
+      English: http://www.aosong.com/userfiles/files/media/Data%20Sheet%20AHT20.pdf
+
 Author: Johannes Cornelis Draaijer <jcdra1@gmail.com>
 
 
 Description
 -----------
 
-The AHT10 is a Temperature and Humidity sensor
+The AHT10/AHT20 is a Temperature and Humidity sensor
 
 The address of this i2c device may only be 0x38
 
+Special Features
+----------------
+
+AHT20 has additional CRC8 support which is sent as the last byte of the sensor
+values.
+
 Usage Notes
 -----------
 
-This driver does not probe for AHT10 devices, as there is no reliable
-way to determine if an i2c chip is or isn't an AHT10. The device has
+This driver does not probe for AHT10/ATH20 devices, as there is no reliable
+way to determine if an i2c chip is or isn't an AHT10/AHT20. The device has
 to be instantiated explicitly with the address 0x38. See
 Documentation/i2c/instantiating-devices.rst for details.
 
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index fc640201a2de..bf73934a6eee 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -255,10 +255,11 @@ config SENSORS_ADT7475
 	  will be called adt7475.
 
 config SENSORS_AHT10
-	tristate "Aosong AHT10"
+	tristate "Aosong AHT10, AHT20"
 	depends on I2C
+	select CRC8
 	help
-	  If you say yes here, you get support for the Aosong AHT10
+	  If you say yes here, you get support for the Aosong AHT10 and AHT20
 	  temperature and humidity sensors
 
 	  This driver can also be built as a module. If so, the module
diff --git a/drivers/hwmon/aht10.c b/drivers/hwmon/aht10.c
index ec7459575c58..f136bf3ff40a 100644
--- a/drivers/hwmon/aht10.c
+++ b/drivers/hwmon/aht10.c
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
 /*
- * aht10.c - Linux hwmon driver for AHT10 Temperature and Humidity sensor
+ * aht10.c - Linux hwmon driver for AHT10/AHT20 Temperature and Humidity sensors
  * Copyright (C) 2020 Johannes Cornelis Draaijer
  */
 
@@ -10,9 +10,13 @@
 #include <linux/i2c.h>
 #include <linux/ktime.h>
 #include <linux/module.h>
+#include <linux/crc8.h>
 
 #define AHT10_MEAS_SIZE		6
 
+#define AHT20_MEAS_SIZE		7
+#define AHT20_CRC8_POLY		0x31
+
 /*
  * Poll intervals (in milliseconds)
  */
@@ -44,9 +48,18 @@
 
 #define AHT10_MAX_POLL_INTERVAL_LEN	30
 
+enum aht10_variant { aht10, aht20 };
+
+static const struct i2c_device_id aht10_id[] = {
+	{ "aht10", aht10 },
+	{ "aht20", aht20 },
+	{ },
+};
+MODULE_DEVICE_TABLE(i2c, aht10_id);
+
 /**
- *   struct aht10_data - All the data required to operate an AHT10 chip
- *   @client: the i2c client associated with the AHT10
+ *   struct aht10_data - All the data required to operate an AHT10/AHT20 chip
+ *   @client: the i2c client associated with the AHT10/AHT20
  *   @lock: a mutex that is used to prevent parallel access to the
  *          i2c client
  *   @min_poll_interval: the minimum poll interval
@@ -56,12 +69,14 @@
  *                   the chip from warming up due to the heat it generates.
  *                   If it's unwanted, it can be ignored setting it to
  *                   it to 0. Default value is 2000 ms
- *   @previous_poll_time: the previous time that the AHT10
+ *   @previous_poll_time: the previous time that the AHT10/AHT20
  *                        was polled
  *   @temperature: the latest temperature value received from
- *                 the AHT10
+ *                 the AHT10/AHT20
  *   @humidity: the latest humidity value received from the
- *              AHT10
+ *              AHT10/AHT20
+ *   @crc8: crc8 support flag
+ *   @meas_size: measurements data size
  */
 
 struct aht10_data {
@@ -75,11 +90,13 @@ struct aht10_data {
 	ktime_t previous_poll_time;
 	int temperature;
 	int humidity;
+	bool crc8;
+	unsigned int meas_size;
 };
 
 /**
- * aht10_init() - Initialize an AHT10 chip
- * @data: the data associated with this AHT10 chip
+ * aht10_init() - Initialize an AHT10/AHT20 chip
+ * @data: the data associated with this AHT10/AHT20 chip
  * Return: 0 if successful, 1 if not
  */
 static int aht10_init(struct aht10_data *data)
@@ -121,8 +138,25 @@ static int aht10_polltime_expired(struct aht10_data *data)
 	return ktime_after(difference, data->min_poll_interval);
 }
 
+DECLARE_CRC8_TABLE(crc8_table);
+
 /**
- * aht10_read_values() - read and parse the raw data from the AHT10
+ * crc8_check() - check crc of the sensor's measurements
+ * @raw_data: data frame received from sensor(including crc as the last byte)
+ * @count: size of the data frame
+ * Return: 0 if successful, 1 if not
+ */
+static int crc8_check(u8 *raw_data, int count)
+{
+	/*
+	 * crc calculated on the whole frame(including crc byte) should yield
+	 * zero in case of correctly received bytes
+	 */
+	return crc8(crc8_table, raw_data, count, CRC8_INIT_VALUE);
+}
+
+/**
+ * aht10_read_values() - read and parse the raw data from the AHT10/AHT20
  * @data: the struct aht10_data to use for the lock
  * Return: 0 if successful, 1 if not
  */
@@ -131,7 +165,7 @@ static int aht10_read_values(struct aht10_data *data)
 	const u8 cmd_meas[] = {AHT10_CMD_MEAS, 0x33, 0x00};
 	u32 temp, hum;
 	int res;
-	u8 raw_data[AHT10_MEAS_SIZE];
+	u8 raw_data[AHT20_MEAS_SIZE];
 	struct i2c_client *client = data->client;
 
 	mutex_lock(&data->lock);
@@ -148,14 +182,19 @@ static int aht10_read_values(struct aht10_data *data)
 
 	usleep_range(AHT10_MEAS_DELAY, AHT10_MEAS_DELAY + AHT10_DELAY_EXTRA);
 
-	res = i2c_master_recv(client, raw_data, AHT10_MEAS_SIZE);
-	if (res != AHT10_MEAS_SIZE) {
+	res = i2c_master_recv(client, raw_data, data->meas_size);
+	if (res != data->meas_size) {
 		mutex_unlock(&data->lock);
 		if (res >= 0)
 			return -ENODATA;
 		return res;
 	}
 
+	if (data->crc8 && crc8_check(raw_data, data->meas_size)) {
+		mutex_unlock(&data->lock);
+		return -EIO;
+	}
+
 	hum =   ((u32)raw_data[1] << 12u) |
 		((u32)raw_data[2] << 4u) |
 		((raw_data[3] & 0xF0u) >> 4u);
@@ -292,6 +331,8 @@ static const struct hwmon_chip_info aht10_chip_info = {
 
 static int aht10_probe(struct i2c_client *client)
 {
+	const struct i2c_device_id *id = i2c_match_id(aht10_id, client);
+	enum aht10_variant variant = id->driver_data;
 	struct device *device = &client->dev;
 	struct device *hwmon_dev;
 	struct aht10_data *data;
@@ -307,6 +348,17 @@ static int aht10_probe(struct i2c_client *client)
 	data->min_poll_interval = ms_to_ktime(AHT10_DEFAULT_MIN_POLL_INTERVAL);
 	data->client = client;
 
+	switch (variant) {
+	case aht20:
+		data->meas_size = AHT20_MEAS_SIZE;
+		data->crc8 = true;
+		crc8_populate_msb(crc8_table, AHT20_CRC8_POLY);
+		break;
+	default:
+		data->meas_size = AHT10_MEAS_SIZE;
+		break;
+	}
+
 	mutex_init(&data->lock);
 
 	res = aht10_init(data);
@@ -326,12 +378,6 @@ static int aht10_probe(struct i2c_client *client)
 	return PTR_ERR_OR_ZERO(hwmon_dev);
 }
 
-static const struct i2c_device_id aht10_id[] = {
-	{ "aht10", 0 },
-	{ },
-};
-MODULE_DEVICE_TABLE(i2c, aht10_id);
-
 static struct i2c_driver aht10_driver = {
 	.driver = {
 		.name = "aht10",
@@ -343,6 +389,6 @@ static struct i2c_driver aht10_driver = {
 module_i2c_driver(aht10_driver);
 
 MODULE_AUTHOR("Johannes Cornelis Draaijer <jcdra1@gmail.com>");
-MODULE_DESCRIPTION("AHT10 Temperature and Humidity sensor driver");
+MODULE_DESCRIPTION("AHT10/AHT20 Temperature and Humidity sensor driver");
 MODULE_VERSION("1.0");
 MODULE_LICENSE("GPL v2");
-- 
2.25.1