Fix false alarm when writing convrate on max6658 (sonic-net#82)

* Fix false alarm when writing convrate on max6658

We found that the max6658 sometimes issues a false alarm when its
convrate is changed, with the current hwmon driver. This workaround
will fix it by stopping the conversion before setting the convrate.

* Avoid affecting other kinds by the change to max6658

patch/driver-hwmon-max6658-fix-write-convrate.patch

@@ -0,0 +1,96 @@
+diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
+index 841f2428..d3e1cc2e 100644
+--- a/drivers/hwmon/lm90.c
++++ b/drivers/hwmon/lm90.c
+@@ -486,6 +486,33 @@ static inline int lm90_select_remote_channel(struct i2c_client *client,
+ 	return 0;
+ }
+
++static int max6657_write_convrate(struct i2c_client *client, int val)
++{
++	int err_c = 0;
++	int err;
++	int config_orig, config_stop;
++
++	/* Save config and stop conversion*/
++	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) {
++		err = i2c_smbus_write_byte_data(client, LM90_REG_W_CONFIG1, config_stop);
++		if (err < 0)
++			return err;
++	}
++
++	/* Set conv rate */
++	err = i2c_smbus_write_byte_data(client, LM90_REG_W_CONVRATE, val);
++
++	/* Revert change to config */
++	if (config_orig != config_stop)
++		err_c = i2c_smbus_write_byte_data(client, LM90_REG_W_CONFIG1, config_orig);
++
++	return err < 0 ? err : err_c;
++}
++
+ /*
+  * Set conversion rate.
+  * client->update_lock must be held when calling this function (unless we are
+@@ -506,7 +533,11 @@ static int lm90_set_convrate(struct i2c_client *client, struct lm90_data *data,
+ 		if (interval >= update_interval * 3 / 4)
+ 			break;
+
+-	err = i2c_smbus_write_byte_data(client, LM90_REG_W_CONVRATE, i);
++	if (data->kind == max6657)
++		err = max6657_write_convrate(client, i);
++	else
++		err = i2c_smbus_write_byte_data(client, LM90_REG_W_CONVRATE, i);
++
+ 	data->update_interval = DIV_ROUND_CLOSEST(update_interval, 64);
+ 	return err;
+ }
+@@ -1512,8 +1543,11 @@ static void lm90_restore_conf(void *_data)
+ 	struct i2c_client *client = data->client;
+
+ 	/* Restore initial configuration */
+-	i2c_smbus_write_byte_data(client, LM90_REG_W_CONVRATE,
+-				  data->convrate_orig);
++	if (data->kind == max6657)
++		max6657_write_convrate(client, data->convrate_orig);
++	else
++		i2c_smbus_write_byte_data(client, LM90_REG_W_CONVRATE,
++					  data->convrate_orig);
+ 	i2c_smbus_write_byte_data(client, LM90_REG_W_CONFIG1,
+ 				  data->config_orig);
+ }
+@@ -1521,6 +1555,7 @@ static void lm90_restore_conf(void *_data)
+ static int lm90_init_client(struct i2c_client *client, struct lm90_data *data)
+ {
+ 	int config, convrate;
++	int err;
+
+ 	convrate = lm90_read_reg(client, LM90_REG_R_CONVRATE);
+ 	if (convrate < 0)
+@@ -1530,12 +1565,21 @@ static int lm90_init_client(struct i2c_client *client, struct lm90_data *data)
+ 	/*
+ 	 * Start the conversions.
+ 	 */
+-	lm90_set_convrate(client, data, 500);	/* 500ms; 2Hz conversion rate */
++	/* 500ms; 2Hz conversion rate */
++	if (data->kind != max6657)
++		lm90_set_convrate(client, data, 500);
++
+ 	config = lm90_read_reg(client, LM90_REG_R_CONFIG1);
+ 	if (config < 0)
+ 		return config;
+ 	data->config_orig = config;
+
++	if (data->kind == max6657) {
++		err = lm90_set_convrate(client, data, 500);
++		if (err < 0)
++			return err;
++	}
++
+ 	/* Check Temperature Range Select */
+ 	if (data->kind == adt7461 || data->kind == tmp451) {
+ 		if (config & 0x04)

patch/series

@@ -27,6 +27,7 @@ kernel-add-kexec-reboot-string.patch
 driver-hwmon-max6620.patch
 driver-hwmon-max6620-fix-rpm-calc.patch
 driver-hwmon-max6620-update.patch
+driver-hwmon-max6658-fix-write-convrate.patch
 driver-hwmon-pmbus-dni_dps460.patch
 driver-hwmon-pmbus-dni_dps460-update-pmbus-core.patch
 driver-hwmon-pmbus-dps1900.patch