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

Guenter Roeck
2021-06-02T10:49:00Z

On Tue, Jun 01, 2021 at 10:01:20AM +0200, Václav Kubernát wrote:
> 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.
>
Correct. I made the same observation. Please feel free to suggest attributes
or some other solution to address the above problems.

Thanks,
Guenter

> 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
> >