[PATCH v2 5/7] thermal: renesas: rzg3e: Add safety check when reading temperature

John Madieu
2025-02-27T13:13:03Z

Becaure reading temperature may fail, add mechanism to panic in case
reading the temperature fails after a given number of trials. This is due
to the thermal core disabling the thermal zone device after a couple of
consecutive attempt failures.

Signed-off-by: John Madieu <john.madieu.xa@bp.renesas.com>
---
v1 -> v2: no changes

drivers/thermal/renesas/rzg3e_thermal.c | 38 +++++++++++++++++++++++--
1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/drivers/thermal/renesas/rzg3e_thermal.c b/drivers/thermal/renesas/rzg3e_thermal.c
index be9e1d118a67..ff80d1b517c8 100644
--- a/drivers/thermal/renesas/rzg3e_thermal.c
+++ b/drivers/thermal/renesas/rzg3e_thermal.c
@@ -83,6 +83,19 @@
#define TSU_TIMEOUT_US 10000
#define TSU_MIN_CLOCK_RATE 24000000

+/*
+ * Number of consecutive errors before shutdown
+ *
+ * While simulating thermal sensor failure, we have noticed that the thermal
+ * core tries to fetch the temperature a couple times and then disable the
+ * thermal zone device. In case of extreme heat, this might lead to SoC
+ * destruction.
+ *
+ * Let's prevent this by limitating the number of failure and panic in
+ * case it happens.
+ */
+#define MAX_TEMP_READ_ERRORS 10
+
/**
* struct rzg3e_thermal_priv - RZ/G3E thermal private data structure
* @base: TSU base address
@@ -93,6 +106,7 @@
* @conv_complete: ADC conversion completion
* @reg_lock: protect shared register access
* @cached_temp: last computed temperature (milliCelsius)
+ * @error_count: Track consecutive errors
* @trmval: trim (calibration) values
*/
struct rzg3e_thermal_priv {
@@ -104,6 +118,7 @@ struct rzg3e_thermal_priv {
struct completion conv_complete;
spinlock_t reg_lock;
int cached_temp;
+ atomic_t error_count;
u32 trmval[2];
};

@@ -200,6 +215,7 @@ static irqreturn_t rzg3e_thermal_adc_irq(int irq, void *dev_id)
static int rzg3e_thermal_get_temp(struct thermal_zone_device *zone, int *temp)
{
struct rzg3e_thermal_priv *priv = thermal_zone_device_priv(zone);
+ int error_count;
u32 val;
int ret;

@@ -217,7 +233,7 @@ static int rzg3e_thermal_get_temp(struct thermal_zone_device *zone, int *temp)
TSU_POLL_DELAY_US, TSU_TIMEOUT_US);
if (ret) {
dev_err(priv->dev, "ADC conversion timed out\n");
- return ret;
+ goto handle_error;
}

/* Start conversion */
@@ -225,15 +241,33 @@ static int rzg3e_thermal_get_temp(struct thermal_zone_device *zone, int *temp)

if (!wait_for_completion_timeout(&priv->conv_complete,
msecs_to_jiffies(100))) {
+ ret = -ETIMEDOUT;
dev_err(priv->dev, "ADC conversion completion timeout\n");
- return -ETIMEDOUT;
+ goto handle_error;
}

scoped_guard(spinlock_irqsave, &priv->reg_lock) {
*temp = priv->cached_temp;
}

+ /* Reset error count on successful read */
+ atomic_set(&priv->error_count, 0);
return 0;
+
+handle_error:
+ error_count = atomic_inc_return(&priv->error_count);
+ if (error_count >= MAX_TEMP_READ_ERRORS) {
+ dev_emerg(priv->dev,
+ "Failed to read temperature %d times, initiating emergency shutdown\n",
+ error_count);
+ mdelay(100);
+ panic("Temperature sensor failure - emergency shutdown");
+ }
+
+ dev_err(priv->dev, "Failed to read temperature (error %d), attempt %d/%d\n",
+ ret, error_count, MAX_TEMP_READ_ERRORS);
+
+ return ret;
}

/* Convert temperature in milliCelsius to raw sensor code */
--
2.25.1