[PATCH 1/2] hwmon: (lm90) Cache configuration register value

[Guenter Roeck <linux@xxxxxxxxxxxx>]

The configuration register does not change on its own. Yet, it is read
in various locations, modified, and written back. Simplify and optimize
the code by caching its value and by only writing it back when needed.

Cc: Boyang Yu <byu@xxxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
 drivers/hwmon/lm90.c | 59 +++++++++++++++++++++++++---------------------------
 1 file changed, 28 insertions(+), 31 deletions(-)

diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
index 40bb308d8dd7..7f35ea0044fd 100644
--- a/drivers/hwmon/lm90.c
+++ b/drivers/hwmon/lm90.c
@@ -459,6 +459,7 @@ struct lm90_data {
 
 	unsigned int update_interval; /* in milliseconds */
 
+	u8 config;		/* Current configuration register value */
 	u8 config_orig;		/* Original configuration register value */
 	u8 convrate_orig;	/* Original conversion rate register value */
 	u16 alert_alarms;	/* Which alarm bits trigger ALERT# */
@@ -554,17 +555,20 @@ static inline int lm90_select_remote_channel(struct i2c_client *client,
 					     struct lm90_data *data,
 					     int channel)
 {
-	int config;
-
 	if (data->kind == max6696) {
-		config = lm90_read_reg(client, LM90_REG_R_CONFIG1);
-		if (config < 0)
-			return config;
-		config &= ~0x08;
+		u8 config = data->config & ~0x08;
+		int err;
+
 		if (channel)
 			config |= 0x08;
-		i2c_smbus_write_byte_data(client, LM90_REG_W_CONFIG1,
-					  config);
+		if (data->config != config) {
+			err = i2c_smbus_write_byte_data(client,
+							LM90_REG_W_CONFIG1,
+							config);
+			if (err)
+				return err;
+			data->config = config;
+		}
 	}
 	return 0;
 }
@@ -572,19 +576,16 @@ static inline int lm90_select_remote_channel(struct i2c_client *client,
 static int lm90_write_convrate(struct i2c_client *client,
 			       struct lm90_data *data, int val)
 {
+	u8 config = data->config;
 	int err;
-	int config_orig, config_stop;
 
 	/* Save config and pause conversion */
 	if (data->flags & LM90_PAUSE_FOR_CONFIG) {
-		config_orig = lm90_read_reg(client, LM90_REG_R_CONFIG1);
-		if (config_orig < 0)
-			return config_orig;
-		config_stop = config_orig | 0x40;
-		if (config_orig != config_stop) {
+		config |= 0x40;
+		if (data->config != config) {
 			err = i2c_smbus_write_byte_data(client,
 							LM90_REG_W_CONFIG1,
-							config_stop);
+							config);
 			if (err < 0)
 				return err;
 		}
@@ -594,9 +595,9 @@ static int lm90_write_convrate(struct i2c_client *client,
 	err = i2c_smbus_write_byte_data(client, LM90_REG_W_CONVRATE, val);
 
 	/* Revert change to config */
-	if (data->flags & LM90_PAUSE_FOR_CONFIG && config_orig != config_stop)
+	if (data->config != config)
 		i2c_smbus_write_byte_data(client, LM90_REG_W_CONFIG1,
-					  config_orig);
+					  data->config);
 
 	return err;
 }
@@ -802,15 +803,12 @@ static int lm90_update_device(struct device *dev)
 		 */
 		if (!(data->config_orig & 0x80) &&
 		    !(data->alarms & data->alert_alarms)) {
-			val = lm90_read_reg(client, LM90_REG_R_CONFIG1);
-			if (val < 0)
-				return val;
-
-			if (val & 0x80) {
+			if (data->config & 0x80) {
 				dev_dbg(&client->dev, "Re-enabling ALERT#\n");
+				data->config &= ~0x80;
 				i2c_smbus_write_byte_data(client,
 							  LM90_REG_W_CONFIG1,
-							  val & ~0x80);
+							  data->config);
 			}
 		}
 
@@ -1648,6 +1646,7 @@ static int lm90_init_client(struct i2c_client *client, struct lm90_data *data)
 	if (config < 0)
 		return config;
 	data->config_orig = config;
+	data->config = config;
 
 	lm90_set_convrate(client, data, 500); /* 500ms; 2Hz conversion rate */
 
@@ -1672,8 +1671,10 @@ static int lm90_init_client(struct i2c_client *client, struct lm90_data *data)
 		config &= ~0x08;
 
 	config &= 0xBF;	/* run */
-	if (config != data->config_orig) /* Only write if changed */
+	if (config != data->config) {	/* Only write if changed */
 		i2c_smbus_write_byte_data(client, LM90_REG_W_CONFIG1, config);
+		data->config = config;
+	}
 
 	return devm_add_action_or_reset(&client->dev, lm90_restore_conf, data);
 }
@@ -1907,14 +1908,10 @@ static void lm90_alert(struct i2c_client *client, enum i2c_alert_protocol type,
 
 		if ((data->flags & LM90_HAVE_BROKEN_ALERT) &&
 		    (alarms & data->alert_alarms)) {
-			int config;
-
 			dev_dbg(&client->dev, "Disabling ALERT#\n");
-			config = lm90_read_reg(client, LM90_REG_R_CONFIG1);
-			if (config >= 0)
-				i2c_smbus_write_byte_data(client,
-							  LM90_REG_W_CONFIG1,
-							  config | 0x80);
+			data->config |= 0x80;
+			i2c_smbus_write_byte_data(client, LM90_REG_W_CONFIG1,
+						  data->config);
 		}
 	} else {
 		dev_info(&client->dev, "Everything OK\n");
-- 
2.7.4