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realtek: hwmon: add LM75 alert pin polarity swap patch

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Allow to configure the LM75 alert pin to active-high instead
of its default active-low. This patch is needed for the D-Link
DGS-1250 series where the alert pin steers the fan speed
between low and high.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/22589
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
This commit is contained in:
Markus Stockhausen 2026-03-24 15:24:21 +01:00 committed by Hauke Mehrtens
parent 1a09f84110
commit eb171568a9
1 changed files with 59 additions and 0 deletions
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59
target/linux/realtek/patches-6.12/810-lm75-alert-polarity-swap.patch Normal file
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@ -0,0 +1,59 @@
From 92ea53e058d40ebda7326016494e3c21dc536c53 Mon Sep 17 00:00:00 2001
From: Markus Stockhausen <markus.stockhausen@gmx.de>
Date: Mon, 23 Mar 2026 22:12:01 +0200
Subject: [PATCH] hwmon: lm75 alert polarity swap
The LM75 can steer the alert polarity. In default mode the alert
output pin is active-low. This can not be configured with the
existing LM75 driver.
There are hardware designs that use this alert output for an automatic
fan speed control. E.g. the D-Link DGS-1250. This works as follows
- temperature below Tmax threshold -> alert pin low -> fan slow speed
- temperature above Tmax threshold -> alert pin high -> fan high speed
As one can see the hardware design requires the alert pin to be
configured in mode active-high to work as described. Add a LM75 DTS
property "alert-polarity-active-high" that allows to swap the alert
pin behaviour during initialization to active-high.
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
--- a/drivers/hwmon/lm75.c
+++ b/drivers/hwmon/lm75.c
@@ -121,7 +121,8 @@ struct lm75_data {
static const u8 lm75_sample_set_masks[] = { 0 << 5, 1 << 5, 2 << 5, 3 << 5 };
-#define LM75_SAMPLE_CLEAR_MASK (3 << 5)
+#define LM75_SAMPLE_CLEAR_MASK (3 << 5)
+#define LM75_ALERT_POLARITY_HIGH BIT(2)
/* The structure below stores the configuration values of the supported devices.
* In case of being supported multiple configurations, the default one must
@@ -631,6 +632,7 @@ static int lm75_probe(struct i2c_client
struct device *hwmon_dev;
struct lm75_data *data;
int status, err;
+ u16 set_mask;
if (!i2c_check_functionality(client->adapter,
I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA))
@@ -680,9 +682,14 @@ static int lm75_probe(struct i2c_client
}
data->orig_conf = status;
data->current_conf = status;
+
+ set_mask = data->params->set_mask;
+ if (of_property_read_bool(dev->of_node, "alert-polarity-active-high")) {
+ pr_info("set lm75 alert to active high\n");
+ set_mask |= LM75_ALERT_POLARITY_HIGH;
+ }
- err = lm75_write_config(data, data->params->set_mask,
- data->params->clr_mask);
+ err = lm75_write_config(data, set_mask, data->params->clr_mask);
if (err)
return err;