[PATCH 3/7] hwmon: (max31790) Fix pwmX_enable attributes

Guenter Roeck
2021-05-26T15:40:43Z

pwmX_enable supports three possible values:

0: Fan control disabled. Duty cycle is fixed to 0%
1: Fan control enabled, pwm mode. Duty cycle is determined by
values written into Target Duty Cycle registers.
2: Fan control enabled, rpm mode
Duty cycle is adjusted such that fan speed matches
the values in Target Count registers

The current code does not do this; instead, it mixes pwm control
configuration with fan speed monitoring configuration. Worse, it
reports that pwm control would be disabled (pwmX_enable==0) when
it is in fact enabled in pwm mode. Part of the problem may be that
the chip sets the "TACH input enable" bit on its own whenever the
mode bit is set to RPM mode, but that doesn't mean that "TACH input
enable" accurately reflects the pwm mode.

Fix it up and only handle pwm control with the pwmX_enable attributes.
In the documentation, clarify that disabling pwm control (pwmX_enable=0)
sets the pwm duty cycle to 0%. In the code, explain why TACH_INPUT_EN
is set together with RPM_MODE.

While at it, only update the configuration register if the configuration
has changed, and only update the cached configuration if updating the
chip configuration was successful.

Cc: Jan Kundrát <jan.kundrat@cesnet.cz>
Cc: Václav Kubernát <kubernat@cesnet.cz>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
Documentation/hwmon/max31790.rst | 2 +-
drivers/hwmon/max31790.c | 41 ++++++++++++++++++++------------
2 files changed, 27 insertions(+), 16 deletions(-)

diff --git a/Documentation/hwmon/max31790.rst b/Documentation/hwmon/max31790.rst
index 54ff0f49e28f..7b097c3b9b90 100644
--- a/Documentation/hwmon/max31790.rst
+++ b/Documentation/hwmon/max31790.rst
@@ -38,7 +38,7 @@ Sysfs entries
fan[1-12]_input RO fan tachometer speed in RPM
fan[1-12]_fault RO fan experienced fault
fan[1-6]_target RW desired fan speed in RPM
-pwm[1-6]_enable RW regulator mode, 0=disabled, 1=manual mode, 2=rpm mode
+pwm[1-6]_enable RW regulator mode, 0=disabled (duty cycle=0%), 1=manual mode, 2=rpm mode
pwm[1-6] RW read: current pwm duty cycle,
write: target pwm duty cycle (0-255)
================== === =======================================================
diff --git a/drivers/hwmon/max31790.c b/drivers/hwmon/max31790.c
index 693497e09ac0..67677c437768 100644
--- a/drivers/hwmon/max31790.c
+++ b/drivers/hwmon/max31790.c
@@ -27,6 +27,7 @@

/* Fan Config register bits */
#define MAX31790_FAN_CFG_RPM_MODE 0x80
+#define MAX31790_FAN_CFG_CTRL_MON 0x10
#define MAX31790_FAN_CFG_TACH_INPUT_EN 0x08
#define MAX31790_FAN_CFG_TACH_INPUT 0x01

@@ -271,12 +272,12 @@ static int max31790_read_pwm(struct device *dev, u32 attr, int channel,
*val = data->pwm[channel] >> 8;
return 0;
case hwmon_pwm_enable:
- if (fan_config & MAX31790_FAN_CFG_RPM_MODE)
+ if (fan_config & MAX31790_FAN_CFG_CTRL_MON)
+ *val = 0;
+ else if (fan_config & MAX31790_FAN_CFG_RPM_MODE)
*val = 2;
- else if (fan_config & MAX31790_FAN_CFG_TACH_INPUT_EN)
- *val = 1;
else
- *val = 0;
+ *val = 1;
return 0;
default:
return -EOPNOTSUPP;
@@ -307,23 +308,33 @@ static int max31790_write_pwm(struct device *dev, u32 attr, int channel,
case hwmon_pwm_enable:
fan_config = data->fan_config[channel];
if (val == 0) {
- fan_config &= ~(MAX31790_FAN_CFG_TACH_INPUT_EN |
- MAX31790_FAN_CFG_RPM_MODE);
+ fan_config |= MAX31790_FAN_CFG_CTRL_MON;
+ /*
+ * Disable RPM mode; otherwise disabling fan speed
+ * monitoring is not possible.
+ */
+ fan_config &= ~MAX31790_FAN_CFG_RPM_MODE;
} else if (val == 1) {
- fan_config = (fan_config |
- MAX31790_FAN_CFG_TACH_INPUT_EN) &
- ~MAX31790_FAN_CFG_RPM_MODE;
+ fan_config &= ~(MAX31790_FAN_CFG_CTRL_MON | MAX31790_FAN_CFG_RPM_MODE);
} else if (val == 2) {
- fan_config |= MAX31790_FAN_CFG_TACH_INPUT_EN |
- MAX31790_FAN_CFG_RPM_MODE;
+ fan_config &= ~MAX31790_FAN_CFG_CTRL_MON;
+ /*
+ * The chip sets MAX31790_FAN_CFG_TACH_INPUT_EN on its
+ * own if MAX31790_FAN_CFG_RPM_MODE is set.
+ * Do it here as well to reflect the actual register
+ * value in the cache.
+ */
+ fan_config |= (MAX31790_FAN_CFG_RPM_MODE | MAX31790_FAN_CFG_TACH_INPUT_EN);
} else {
err = -EINVAL;
break;
}
- data->fan_config[channel] = fan_config;
- err = i2c_smbus_write_byte_data(client,
- MAX31790_REG_FAN_CONFIG(channel),
- fan_config);
+ if (fan_config != data->fan_config[channel]) {
+ err = i2c_smbus_write_byte_data(client, MAX31790_REG_FAN_CONFIG(channel),
+ fan_config);
+ if (!err)
+ data->fan_config[channel] = fan_config;
+ }
break;
default:
err = -EOPNOTSUPP;
--
2.25.1