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

[Guenter Roeck <linux@roeck-us.net>]

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
> >