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

Václav Kubernát
2021-06-01T08:01:37Z

pwmX_enable 0 and 1 work fine, but it seems like RPM mode is currently
still unusable. I am testing with Sunon PF36281BX-000U-S99. Setting
almost any kind of RPM, from low (about 2500) and high (maximum is
23000), the RPM never stabilizes. I think this is mainly because the
driver currently doesn't work with the "window" and "pwm rate of
change" registers.

Tested-by: Václav Kubernát <kubernat@cesnet.cz>

st 26. 5. 2021 v 17:40 odesílatel Guenter Roeck <linux@roeck-us.net> napsal:
>
> 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
>