Re: [PATCH v5 2/5] hwmon: (max31790) Fix and split pwm*_enable

From: Guenter Roeck
Date: Wed May 19 2021 - 19:11:11 EST

On 5/11/21 6:30 PM, Václav Kubernát wrote:
In the old code, pwm*_enable does two things. Firstly, it sets whether
the chip should run in PWM or RPM mode. Secondly, it tells the chip
whether it should monitor fan RPM. However, these two settings aren't
tied together, so they shouldn't be set with a single value. In the new
code, fan*_enable now controls fan RPM monitoring (pwm*_enable no longer
controls that).

According to the sysfs hwmon documentation, pwm*_enable has three
possible values, 0 for "no control / full-speed", 1 for manual mode, and
2+ for automatic. The old code works fine for 1 and 2, but 0 only
differs from 1 in that it just turns off fan speed monitoring. The chip
actually does have a way to turn off fan controls (and only monitor),
and what that does is that it sets PWM to 0% duty cycle. In the new
code, 0 in pwm*_enable turns off the "control" feature of the chip.

These two changes are closely connected together, mainly because the
detection of the pwm*_enable value depended on whether fan speed
monitoring is enabled (which is now controlled as written in the first
paragraph).

The above is an indication that the current code is simply wrong.
pwmX_enable does not and should not have anything to do with
fan speed monitoring (even though it may implicitly enable it).

Fixing pwmX_enable therefore needs to be a separate patch from
introducing fanX_enable, and like the other fixes it needs to come
first, before changing the code to use regmap (to enable backporting).

More comments below.

Thanks,
Guenter

Signed-off-by: Václav Kubernát <kubernat@xxxxxxxxx>
---
Documentation/hwmon/max31790.rst | 10 ++--
drivers/hwmon/max31790.c | 78 +++++++++++++++++++++-----------
2 files changed, 58 insertions(+), 30 deletions(-)

diff --git a/Documentation/hwmon/max31790.rst b/Documentation/hwmon/max31790.rst
index f301385d8cef..d2ac4e926905 100644
--- a/Documentation/hwmon/max31790.rst
+++ b/Documentation/hwmon/max31790.rst
@@ -34,10 +34,14 @@ also be configured to serve as tachometer inputs.
Sysfs entries
-------------
-================== === =======================================================
+================== === =============================================================
+fan[1-12]_enable RW enable fan speed monitoring
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=no control, sets 0% PWM,
+ 1=manual (pwm) mode,
+ 2=rpm mode
+ setting rpm mode sets fan*_enable to 1
pwm[1-6] RW fan target duty cycle (0-255)
-================== === =======================================================
+================== === =============================================================
diff --git a/drivers/hwmon/max31790.c b/drivers/hwmon/max31790.c
index e3765ce4444a..5d4c551df010 100644
--- a/drivers/hwmon/max31790.c
+++ b/drivers/hwmon/max31790.c
@@ -30,6 +30,7 @@
#define MAX31790_FAN_CFG_RPM_MODE 0x80
#define MAX31790_FAN_CFG_TACH_INPUT_EN 0x08
#define MAX31790_FAN_CFG_TACH_INPUT 0x01
+#define MAX31790_FAN_CFG_CTRL_MON 0x10

This define should be above MAX31790_FAN_CFG_TACH_INPUT_EN
to maintain sequence/order.

/* Fan Dynamics register bits */
#define MAX31790_FAN_DYN_SR_SHIFT 5
@@ -191,6 +192,9 @@ static int max31790_read_fan(struct device *dev, u32 attr, int channel,
else
*val = !!(fault & (1 << channel));
return 0;
+ case hwmon_fan_enable:
+ *val = !!(data->fan_config[channel] & MAX31790_FAN_CFG_TACH_INPUT_EN);
+ return 0;
default:
return -EOPNOTSUPP;
}
@@ -233,6 +237,15 @@ static int max31790_write_fan(struct device *dev, u32 attr, int channel,
MAX31790_REG_TARGET_COUNT(channel),
target_count);
break;
+ case hwmon_fan_enable:
+ if (val == 0)
+ data->fan_config[channel] &= ~MAX31790_FAN_CFG_TACH_INPUT_EN;
+ else
+ data->fan_config[channel] |= MAX31790_FAN_CFG_TACH_INPUT_EN;
+ err = regmap_write(regmap,
+ MAX31790_REG_FAN_CONFIG(channel),
+ data->fan_config[channel]);
+ break;
default:
err = -EOPNOTSUPP;
break;
@@ -260,6 +273,11 @@ static umode_t max31790_fan_is_visible(const void *_data, u32 attr, int channel)
!(fan_config & MAX31790_FAN_CFG_TACH_INPUT))
return 0644;
return 0;
+ case hwmon_fan_enable:
+ if (channel < NR_CHANNEL ||
+ (fan_config & MAX31790_FAN_CFG_TACH_INPUT))
+ return 0644;
+ return 0;
default:
return 0;
}
@@ -281,12 +299,12 @@ static int max31790_read_pwm(struct device *dev, u32 attr, int channel,
*val = read >> 8;
return 0;
case hwmon_pwm_enable:
- if (data->fan_config[channel] & MAX31790_FAN_CFG_RPM_MODE)
+ if (data->fan_config[channel] & MAX31790_FAN_CFG_CTRL_MON)
+ *val = 0;
+ else if (data->fan_config[channel] & MAX31790_FAN_CFG_RPM_MODE)
*val = 2;
- else if (data->fan_config[channel] & MAX31790_FAN_CFG_TACH_INPUT_EN)
+ else
*val = 1;
- else
- *val = 0;
return 0;
default:
return -EOPNOTSUPP;
@@ -298,35 +316,41 @@ static int max31790_write_pwm(struct device *dev, u32 attr, int channel,
{
struct max31790_data *data = dev_get_drvdata(dev);
struct regmap *regmap = data->regmap;
- u8 fan_config;
+ u8 fan_config = data->fan_config[channel];
int err = 0;
mutex_lock(&data->update_lock);
switch (attr) {
case hwmon_pwm_input:
- if (val < 0 || val > 255) {
+ if (fan_config & MAX31790_FAN_CFG_CTRL_MON || val < 0 || val > 255) {

No. It has to be possible to set the target pwm value before enabling pwm control.

err = -EINVAL;
break;
}
+
err = write_reg_word(regmap, MAX31790_REG_PWMOUT(channel), val << 8);
break;
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);
- } else if (val == 1) {
- fan_config = (fan_config |
- MAX31790_FAN_CFG_TACH_INPUT_EN) &
- ~MAX31790_FAN_CFG_RPM_MODE;
+ if (val == 0)
+ fan_config |= MAX31790_FAN_CFG_CTRL_MON;
+ else if (val == 1) {
+ fan_config &= ~(MAX31790_FAN_CFG_RPM_MODE | MAX31790_FAN_CFG_CTRL_MON);
} else if (val == 2) {
- fan_config |= MAX31790_FAN_CFG_TACH_INPUT_EN |
- MAX31790_FAN_CFG_RPM_MODE;
+ fan_config &= ~(MAX31790_FAN_CFG_CTRL_MON);

Unnecessary ( )

+ fan_config |= MAX31790_FAN_CFG_RPM_MODE;
} else {
err = -EINVAL;
break;
}
+
+ /*
+ * RPM mode implies enabled TACH input, so enable it in RPM
+ * mode.
+ */
+ if (val == 2)
+ fan_config |= MAX31790_FAN_CFG_TACH_INPUT_EN;
+

The datasheet says this is automatically enabled in rpm mode, meaning there
is no need to explicitly set the bit. I don't know if the bit is set
automatically. If not, it should not be set here. Either case, there is
already an "if (val ==2)" check above. If needed, this bit should be set there.

data->fan_config[channel] = fan_config;
err = regmap_write(regmap,
MAX31790_REG_FAN_CONFIG(channel),
@@ -400,18 +424,18 @@ static umode_t max31790_is_visible(const void *data,
static const struct hwmon_channel_info *max31790_info[] = {
HWMON_CHANNEL_INFO(fan,
- HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
- HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
- HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
- HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
- HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
- HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
- HWMON_F_INPUT | HWMON_F_FAULT,
- HWMON_F_INPUT | HWMON_F_FAULT,
- HWMON_F_INPUT | HWMON_F_FAULT,
- HWMON_F_INPUT | HWMON_F_FAULT,
- HWMON_F_INPUT | HWMON_F_FAULT,
- HWMON_F_INPUT | HWMON_F_FAULT),
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_FAULT,
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_FAULT,
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_FAULT,
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_FAULT,
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_FAULT,
+ HWMON_F_ENABLE | HWMON_F_INPUT | HWMON_F_FAULT),
HWMON_CHANNEL_INFO(pwm,
HWMON_PWM_INPUT | HWMON_PWM_ENABLE,
HWMON_PWM_INPUT | HWMON_PWM_ENABLE,