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

["Václav Kubernát" <kubernat@cesnet.cz>]

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
>