[PATCH v2 2/4] thermal/drivers/airoha: Serialise access to the shared ADC
From: Vitaliy Sochnev
Date: Tue Sep 15 2026 - 13:28:51 EST
A read selects the sensor and walks three diodes with a 10 ms settle on
each. Nothing serialises this, so concurrent reads interleave and
convert samples taken at another mux position.
Mux writes are dropped silently unless PLLRG_PROTECT is lifted, and its
save and restore do not nest. The cached TADC value also skips a write
after another reader has moved the mux.
With the AN7583 sensors read as parallel zones during CPU frequency
changes, a zone crossed its critical trip on a chip at 55 C and the
board shut down.
Serialise the sequence, drop the cache, check the selection after
writing and after sampling, and return -EAGAIN if it does not hold.
Signed-off-by: Vitaliy Sochnev <sochnev.v.74@xxxxxxxxx>
---
drivers/thermal/airoha_thermal.c | 85 +++++++++++++++++++++++++-------
1 file changed, 68 insertions(+), 17 deletions(-)
diff --git a/drivers/thermal/airoha_thermal.c b/drivers/thermal/airoha_thermal.c
index 2934d6aba0ed..d7e4a088b7ea 100644
--- a/drivers/thermal/airoha_thermal.c
+++ b/drivers/thermal/airoha_thermal.c
@@ -5,6 +5,7 @@
#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/mfd/syscon.h>
+#include <linux/mutex.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/platform_device.h>
@@ -191,6 +192,7 @@
#define AN7583_NUM_SENSOR 3
#define AIROHA_THERMAL_NO_MUX_SENSOR -1
+#define AIROHA_THERMAL_MUX_TRIES 3
/* Convert temp to raw value as read from ADC ((((temp / 100) - init) * slope) / 1000) + offset */
#define TEMP_TO_RAW(priv, temp) ((((((temp) / 100) - (priv)->init_temp) * \
@@ -250,7 +252,8 @@ struct airoha_thermal_priv {
struct resource scu_adc_res;
u32 pllrg_protect;
- int current_adc;
+ /* Serialises mux selection and ADC sampling */
+ struct mutex lock;
struct thermal_zone_device *tz;
int init_temp;
@@ -294,9 +297,26 @@ static int airoha_get_thermal_ADC(struct airoha_thermal_priv *priv)
return val;
}
+static bool airoha_thermal_mux_holds(struct airoha_thermal_priv *priv,
+ int tdac_idx, int sensor_idx)
+{
+ unsigned int val;
+
+ if (regmap_field_read(priv->chip_scu_fields[AIROHA_THERMAL_MUX_TADC], &val) ||
+ val != tdac_idx)
+ return false;
+
+ if (sensor_idx == AIROHA_THERMAL_NO_MUX_SENSOR)
+ return true;
+
+ return !regmap_field_read(priv->chip_scu_fields[AIROHA_THERMAL_MUX_SENSOR], &val) &&
+ val == sensor_idx;
+}
+
static void airoha_set_thermal_mux(struct airoha_thermal_priv *priv,
int tdac_idx, int sensor_idx)
{
+ int tries = AIROHA_THERMAL_MUX_TRIES;
u32 pllrg;
/* Save PLLRG current value */
@@ -307,19 +327,17 @@ static void airoha_set_thermal_mux(struct airoha_thermal_priv *priv,
priv->pllrg_protect);
/*
- * Configure Thermal Sensor mux to sensor_idx.
+ * Configure Thermal Sensor mux to sensor_idx and Thermal ADC mux to
+ * tdac_idx. Writes can be dropped silently, so read them back.
* (if not supported, sensor_idx is AIROHA_THERMAL_NO_MUX_SENSOR)
*/
- if (sensor_idx != AIROHA_THERMAL_NO_MUX_SENSOR)
- regmap_field_write(priv->chip_scu_fields[AIROHA_THERMAL_MUX_SENSOR],
- sensor_idx);
-
- /* Configure Thermal ADC mux to tdac_idx */
- if (priv->current_adc != tdac_idx) {
+ do {
+ if (sensor_idx != AIROHA_THERMAL_NO_MUX_SENSOR)
+ regmap_field_write(priv->chip_scu_fields[AIROHA_THERMAL_MUX_SENSOR],
+ sensor_idx);
regmap_field_write(priv->chip_scu_fields[AIROHA_THERMAL_MUX_TADC],
tdac_idx);
- priv->current_adc = tdac_idx;
- }
+ } while (!airoha_thermal_mux_holds(priv, tdac_idx, sensor_idx) && --tries);
/* Restore PLLRG value on exit */
regmap_write(priv->chip_scu, EN7581_PLLRG_PROTECT, pllrg);
@@ -594,12 +612,40 @@ static int en7581_thermal_post_probe(struct platform_device *pdev)
return 0;
}
+static int an7583_thermal_read_diode(struct airoha_thermal_priv *priv,
+ int diode, int sensor_idx, int *val)
+{
+ airoha_set_thermal_mux(priv, diode, sensor_idx);
+ *val = airoha_get_thermal_ADC(priv);
+
+ return airoha_thermal_mux_holds(priv, diode, sensor_idx) ? 0 : -EAGAIN;
+}
+
+static int an7583_thermal_read_diodes(struct airoha_thermal_priv *priv,
+ int sensor_idx, int *zero, int *d0,
+ int *d1)
+{
+ int ret;
+
+ ret = an7583_thermal_read_diode(priv, AN7583_ZERO_TADC, sensor_idx, zero);
+ if (ret)
+ return ret;
+
+ ret = an7583_thermal_read_diode(priv, AN7583_D0_TADC, sensor_idx, d0);
+ if (ret)
+ return ret;
+
+ return an7583_thermal_read_diode(priv, AN7583_D1_TADC, sensor_idx, d1);
+}
+
static int an7583_thermal_get_temp(struct thermal_zone_device *tz, int *temp)
{
struct airoha_thermal_priv *priv = thermal_zone_device_priv(tz);
int sensor_idx;
int delta_diode, delta_gain;
int coeff, slope, offset;
+ int tries = AIROHA_THERMAL_MUX_TRIES;
+ int ret;
int diode_zero, diode_d0, diode_d1;
@@ -610,12 +656,14 @@ static int an7583_thermal_get_temp(struct thermal_zone_device *tz, int *temp)
slope = an7583_thermal_slope[sensor_idx];
offset = an7583_thermal_offset[sensor_idx];
- airoha_set_thermal_mux(priv, AN7583_ZERO_TADC, sensor_idx);
- diode_zero = airoha_get_thermal_ADC(priv);
- airoha_set_thermal_mux(priv, AN7583_D0_TADC, sensor_idx);
- diode_d0 = airoha_get_thermal_ADC(priv);
- airoha_set_thermal_mux(priv, AN7583_D1_TADC, sensor_idx);
- diode_d1 = airoha_get_thermal_ADC(priv);
+ mutex_lock(&priv->lock);
+ do {
+ ret = an7583_thermal_read_diodes(priv, sensor_idx, &diode_zero,
+ &diode_d0, &diode_d1);
+ } while (ret == -EAGAIN && --tries);
+ mutex_unlock(&priv->lock);
+ if (ret)
+ return ret;
delta_diode = diode_d1 - diode_d0;
delta_gain = (delta_diode * coeff) / 100 + (diode_zero - diode_d1);
@@ -676,7 +724,10 @@ static int airoha_thermal_probe(struct platform_device *pdev)
return -ENOMEM;
priv->pllrg_protect = soc_data->pllrg_protect;
- priv->current_adc = -1;
+
+ ret = devm_mutex_init(dev, &priv->lock);
+ if (ret)
+ return ret;
if (!soc_data->probe)
return -EINVAL;
--
2.55.0