[PATCH 0/3] hwmon: (max31760) Fix local limits, standby and the initial fan speed

[PATCH 0/3] hwmon: (max31760) Fix local limits, standby and the initial fan speed

[Stanislav Aleksandrov]

Three fixes for the MAX31760 driver, found while bringing up the Samsung
Galaxy XR on mainline. The headset uses the chip for its two cooling
fans.

1. The local temperature max and crit limits are swapped.
2. Probe never clears the standby bit. The Galaxy XR bootloader leaves
   the chip in standby, so the driver gets no temperature or fan speed
   readings and can't control the fans.
3. The fan speed reads 3000000 RPM before the first measurement.

The patches were written with the help of an AI coding assistant
(Claude Code), based on the datasheet and tests on the device. I
reviewed them and tested them on the Galaxy XR.

---
Stanislav Aleksandrov (3):
      hwmon: (max31760) Fix the local temperature limit registers
      hwmon: (max31760) Leave standby mode at probe
      hwmon: (max31760) Report 0 RPM before the first fan speed measurement

 drivers/hwmon/max31760.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)
---
base-commit: f4e680ffc2e50867c5b590e26a37f8801a31e486
change-id: 20261108-max31760-fixes-0af187603717

Best regards,
--  
Stanislav Aleksandrov <lightofmysoul@gmail.com>

[PATCH 1/3] hwmon: (max31760) Fix the local temperature limit registers

[Stanislav Aleksandrov]

temp2_max and temp2_crit use each other's registers, so reading them
shows the local limits swapped and writing temp2_max changes the
overtemperature (SHDN) threshold.

Use the high limit (0x0C) for temp2_max and the overtemperature limit
(0x08) for temp2_crit.

Fixes: 38b04ad02d0d ("drivers: hwmon: Add max31760 fan speed controller driver")
Signed-off-by: Stanislav Aleksandrov <lightofmysoul@gmail.com>
---
 drivers/hwmon/max31760.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/max31760.c b/drivers/hwmon/max31760.c
index 8d3be064b025..e3d86dc4257e 100644
--- a/drivers/hwmon/max31760.c
+++ b/drivers/hwmon/max31760.c
@@ -27,8 +27,8 @@
 
 #define REG_TACH(ch)		(0x52 + (ch) * 2)
 #define REG_TEMP_INPUT(ch)	(0x56 + (ch) * 2)
-#define REG_TEMP_MAX(ch)	(0x06 + (ch) * 2)
-#define REG_TEMP_CRIT(ch)	(0x0A + (ch) * 2)
+#define REG_TEMP_MAX(ch)	((ch) ? 0x0C : 0x06)
+#define REG_TEMP_CRIT(ch)	((ch) ? 0x08 : 0x0A)
 
 #define TEMP11_FROM_REG(reg)	((reg) / 32 * 125)
 #define TEMP11_TO_REG(val)	(DIV_ROUND_CLOSEST(clamp_val((val), -128000, \

-- 
2.55.0

Re: [PATCH 1/3] hwmon: (max31760) Fix the local temperature limit registers

[Guenter Roeck]

On Sun, Nov 08, 2026 at 03:59:53AM +0000, Stanislav Aleksandrov wrote:
> temp2_max and temp2_crit use each other's registers, so reading them
> shows the local limits swapped and writing temp2_max changes the
> overtemperature (SHDN) threshold.
> 
> Use the high limit (0x0C) for temp2_max and the overtemperature limit
> (0x08) for temp2_crit.
> 
> Fixes: 38b04ad02d0d ("drivers: hwmon: Add max31760 fan speed controller driver")
> Signed-off-by: Stanislav Aleksandrov <lightofmysoul@gmail.com>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/max31760.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/max31760.c b/drivers/hwmon/max31760.c
> index 8d3be064b025..e3d86dc4257e 100644
> --- a/drivers/hwmon/max31760.c
> +++ b/drivers/hwmon/max31760.c
> @@ -27,8 +27,8 @@
>  
>  #define REG_TACH(ch)		(0x52 + (ch) * 2)
>  #define REG_TEMP_INPUT(ch)	(0x56 + (ch) * 2)
> -#define REG_TEMP_MAX(ch)	(0x06 + (ch) * 2)
> -#define REG_TEMP_CRIT(ch)	(0x0A + (ch) * 2)
> +#define REG_TEMP_MAX(ch)	((ch) ? 0x0C : 0x06)
> +#define REG_TEMP_CRIT(ch)	((ch) ? 0x08 : 0x0A)
>  
>  #define TEMP11_FROM_REG(reg)	((reg) / 32 * 125)
>  #define TEMP11_TO_REG(val)	(DIV_ROUND_CLOSEST(clamp_val((val), -128000, \

[PATCH 2/3] hwmon: (max31760) Leave standby mode at probe

[Stanislav Aleksandrov]

The driver never clears the standby bit (CR2_STBY) during probe.
While max31760_resume() clears this bit on resume, probe only
configured CR2_ALERTS.

If the chip was left in standby (for example, by boot firmware or a
previously running OS before a warm reboot), it remains in standby:
temperature sensing, fan speed counting, and PWM output are halted.
This occurs on the Samsung Galaxy XR, where the bootloader places the
chip in standby during boot.

Clear CR2_STBY alongside setting CR2_ALERTS in probe.

Fixes: 38b04ad02d0d ("drivers: hwmon: Add max31760 fan speed controller driver")
Signed-off-by: Stanislav Aleksandrov <lightofmysoul@gmail.com>
---
 drivers/hwmon/max31760.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/max31760.c b/drivers/hwmon/max31760.c
index e3d86dc4257e..e967555a21af 100644
--- a/drivers/hwmon/max31760.c
+++ b/drivers/hwmon/max31760.c
@@ -533,8 +533,9 @@ static int max31760_probe(struct i2c_client *client)
 
 	dev_set_drvdata(dev, state);
 
-	/* Set alert output to comparator mode */
-	ret = regmap_set_bits(state->regmap, REG_CR2, CR2_ALERTS);
+	/* Leave standby mode, set alert output to comparator mode */
+	ret = regmap_update_bits(state->regmap, REG_CR2, CR2_STBY | CR2_ALERTS,
+				 CR2_ALERTS);
 	if (ret)
 		return dev_err_probe(dev, ret, "cannot write register\n");
 

-- 
2.55.0

Re: [PATCH 2/3] hwmon: (max31760) Leave standby mode at probe

[Guenter Roeck]

On Sun, Nov 08, 2026 at 03:59:54AM +0000, Stanislav Aleksandrov wrote:
> The driver never clears the standby bit (CR2_STBY) during probe.
> While max31760_resume() clears this bit on resume, probe only
> configured CR2_ALERTS.
> 
> If the chip was left in standby (for example, by boot firmware or a
> previously running OS before a warm reboot), it remains in standby:
> temperature sensing, fan speed counting, and PWM output are halted.
> This occurs on the Samsung Galaxy XR, where the bootloader places the
> chip in standby during boot.
> 
> Clear CR2_STBY alongside setting CR2_ALERTS in probe.
> 
> Fixes: 38b04ad02d0d ("drivers: hwmon: Add max31760 fan speed controller driver")
> Signed-off-by: Stanislav Aleksandrov <lightofmysoul@gmail.com>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/max31760.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/max31760.c b/drivers/hwmon/max31760.c
> index e3d86dc4257e..e967555a21af 100644
> --- a/drivers/hwmon/max31760.c
> +++ b/drivers/hwmon/max31760.c
> @@ -533,8 +533,9 @@ static int max31760_probe(struct i2c_client *client)
>  
>  	dev_set_drvdata(dev, state);
>  
> -	/* Set alert output to comparator mode */
> -	ret = regmap_set_bits(state->regmap, REG_CR2, CR2_ALERTS);
> +	/* Leave standby mode, set alert output to comparator mode */
> +	ret = regmap_update_bits(state->regmap, REG_CR2, CR2_STBY | CR2_ALERTS,
> +				 CR2_ALERTS);
>  	if (ret)
>  		return dev_err_probe(dev, ret, "cannot write register\n");
>  

[PATCH 3/3] hwmon: (max31760) Report 0 RPM before the first fan speed measurement

[Stanislav Aleksandrov]

The tachometer count registers initialize to 0 until the first
measurement cycle completes after power-on. To prevent division by
zero, tach_to_rpm() clamped tach == 0 to 1, causing it to compute
and report 3,000,000 RPM (60 * 100000 / 1 / 2).

Return 0 RPM when tach == 0 instead.

Fixes: 38b04ad02d0d ("drivers: hwmon: Add max31760 fan speed controller driver")
Signed-off-by: Stanislav Aleksandrov <lightofmysoul@gmail.com>
---
 drivers/hwmon/max31760.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/max31760.c b/drivers/hwmon/max31760.c
index e967555a21af..896bd0326b8c 100644
--- a/drivers/hwmon/max31760.c
+++ b/drivers/hwmon/max31760.c
@@ -68,8 +68,9 @@ static const int max31760_pwm_freq[] = {33, 150, 1500, 25000};
 
 static int tach_to_rpm(u16 tach)
 {
+	/* The count is 0 until the first measurement */
 	if (tach == 0)
-		tach = 1;
+		return 0;
 
 	return 60 * 100000 / tach / 2;
 }

-- 
2.55.0

Re: [PATCH 3/3] hwmon: (max31760) Report 0 RPM before the first fan speed measurement

[Guenter Roeck]

On Sun, Nov 08, 2026 at 03:59:55AM +0000, Stanislav Aleksandrov wrote:
> The tachometer count registers initialize to 0 until the first
> measurement cycle completes after power-on. To prevent division by
> zero, tach_to_rpm() clamped tach == 0 to 1, causing it to compute
> and report 3,000,000 RPM (60 * 100000 / 1 / 2).
> 
> Return 0 RPM when tach == 0 instead.
> 
> Fixes: 38b04ad02d0d ("drivers: hwmon: Add max31760 fan speed controller driver")
> Signed-off-by: Stanislav Aleksandrov <lightofmysoul@gmail.com>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/max31760.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/max31760.c b/drivers/hwmon/max31760.c
> index e967555a21af..896bd0326b8c 100644
> --- a/drivers/hwmon/max31760.c
> +++ b/drivers/hwmon/max31760.c
> @@ -68,8 +68,9 @@ static const int max31760_pwm_freq[] = {33, 150, 1500, 25000};
>  
>  static int tach_to_rpm(u16 tach)
>  {
> +	/* The count is 0 until the first measurement */
>  	if (tach == 0)
> -		tach = 1;
> +		return 0;
>  
>  	return 60 * 100000 / tach / 2;
>  }