From 62456189f3292c62f87aef363f204886dc1d4b48 Mon Sep 17 00:00:00 2001 From: Boyang Yu Date: Fri, 28 Jun 2019 19:06:36 +0000 Subject: [PATCH] hwmon: (lm90) Fix max6658 sporadic wrong temperature reading max6658 may report unrealistically high temperature during the driver initialization, for which, its overtemp alarm pin also gets asserted. For certain devices implementing overtemp protection based on that pin, it may further trigger a reset to the device. By reproducing the problem, the wrong reading is found to be coincident with changing the conversion rate. To mitigate this issue, set the stop bit before changing the conversion rate and unset it thereafter. After such change, the wrong reading is not reproduced. Apply this change only to the max6657 kind for now, controlled by flag LM90_PAUSE_ON_CONFIG. Signed-off-by: Boyang Yu Signed-off-by: Guenter Roeck --- drivers/hwmon/lm90.c | 42 ++++++++++++++++++++++++++++++++++++++---- 1 file changed, 38 insertions(+), 4 deletions(-) diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c index 2ebcab8b0a9b..40bb308d8dd7 100644 --- a/drivers/hwmon/lm90.c +++ b/drivers/hwmon/lm90.c @@ -174,6 +174,7 @@ enum chips { lm90, adm1032, lm99, lm86, max6657, max6659, adt7461, max6680, #define LM90_HAVE_EMERGENCY_ALARM (1 << 5)/* emergency alarm */ #define LM90_HAVE_TEMP3 (1 << 6) /* 3rd temperature sensor */ #define LM90_HAVE_BROKEN_ALERT (1 << 7) /* Broken alert */ +#define LM90_PAUSE_FOR_CONFIG (1 << 8) /* Pause conversion for config */ /* LM90 status */ #define LM90_STATUS_LTHRM (1 << 0) /* local THERM limit tripped */ @@ -367,6 +368,7 @@ static const struct lm90_params lm90_params[] = { .reg_local_ext = MAX6657_REG_R_LOCAL_TEMPL, }, [max6657] = { + .flags = LM90_PAUSE_FOR_CONFIG, .alert_alarms = 0x7c, .max_convrate = 8, .reg_local_ext = MAX6657_REG_R_LOCAL_TEMPL, @@ -567,6 +569,38 @@ static inline int lm90_select_remote_channel(struct i2c_client *client, return 0; } +static int lm90_write_convrate(struct i2c_client *client, + struct lm90_data *data, int val) +{ + 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) { + 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 (data->flags & LM90_PAUSE_FOR_CONFIG && config_orig != config_stop) + i2c_smbus_write_byte_data(client, LM90_REG_W_CONFIG1, + config_orig); + + return err; +} + /* * Set conversion rate. * client->update_lock must be held when calling this function (unless we are @@ -587,7 +621,7 @@ 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); + err = lm90_write_convrate(client, data, i); data->update_interval = DIV_ROUND_CLOSEST(update_interval, 64); return err; } @@ -1593,8 +1627,7 @@ 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); + lm90_write_convrate(client, data, data->convrate_orig); i2c_smbus_write_byte_data(client, LM90_REG_W_CONFIG1, data->config_orig); } @@ -1611,12 +1644,13 @@ 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 */ config = lm90_read_reg(client, LM90_REG_R_CONFIG1); if (config < 0) return config; data->config_orig = config; + lm90_set_convrate(client, data, 500); /* 500ms; 2Hz conversion rate */ + /* Check Temperature Range Select */ if (data->kind == adt7461 || data->kind == tmp451) { if (config & 0x04)