[PATCH v2 1/2] thermal: qcom: tsens: atomic temperature read with hardware-guided retries

[Priyansh Jain <priyansh.jain@oss.qualcomm.com>]

The existing TSENS temperature read logic polls the valid bit and then
reads the temperature register. When temperature reads are triggered
at very short intervals, this can race with hardware updates and allow
the temperature field to be read while it is still being updated.

In this case, the valid bit may already be asserted even though the
temperature value is transitioning, resulting in an incorrect reading.

Hardware programming guidelines require the temperature value and the
valid bit to be sampled atomically in the same read transaction. A
reading is considered valid only if the valid bit is observed set in
that same sample.

The guidelines further specify that software should attempt the
temperature read up to three times to account for transient update
windows. If none of the attempts observe a valid sample, a stable
fallback value must be returned: if the first and second samples match,
the second value is returned; otherwise, if the second and third
samples match, the third value is returned.

Update the TSENS sensor read logic to implement atomic sampling along
with the recommended retry-and-compare fallback behavior. This removes
the race window and ensures deterministic temperature values in
accordance with hardware requirements.

Signed-off-by: Priyansh Jain <priyansh.jain@oss.qualcomm.com>
---
 drivers/thermal/qcom/tsens-v0_1.c |   1 +
 drivers/thermal/qcom/tsens-v1.c   |   4 ++
 drivers/thermal/qcom/tsens-v2.c   |   6 ++
 drivers/thermal/qcom/tsens.c      | 114 ++++++++++++++++++++----------
 drivers/thermal/qcom/tsens.h      |   7 ++
 5 files changed, 96 insertions(+), 36 deletions(-)

diff --git a/drivers/thermal/qcom/tsens-v0_1.c b/drivers/thermal/qcom/tsens-v0_1.c
index 32d2d3e33287..9426646d1124 100644
--- a/drivers/thermal/qcom/tsens-v0_1.c
+++ b/drivers/thermal/qcom/tsens-v0_1.c
@@ -287,6 +287,7 @@ static struct tsens_features tsens_v0_1_feat = {
 	.max_sensors	= 11,
 	.trip_min_temp	= -40000,
 	.trip_max_temp	= 120000,
+	.last_temp_resolution = 9,
 };
 
 static const struct reg_field tsens_v0_1_regfields[MAX_REGFIELDS] = {
diff --git a/drivers/thermal/qcom/tsens-v1.c b/drivers/thermal/qcom/tsens-v1.c
index faa5d00788ca..c0263375b771 100644
--- a/drivers/thermal/qcom/tsens-v1.c
+++ b/drivers/thermal/qcom/tsens-v1.c
@@ -77,6 +77,8 @@ static struct tsens_features tsens_v1_feat = {
 	.max_sensors	= 11,
 	.trip_min_temp	= -40000,
 	.trip_max_temp	= 120000,
+	.valid_bit = BIT(14),
+	.last_temp_resolution = 9,
 };
 
 static struct tsens_features tsens_v1_no_rpm_feat = {
@@ -88,6 +90,8 @@ static struct tsens_features tsens_v1_no_rpm_feat = {
 	.max_sensors	= 11,
 	.trip_min_temp	= -40000,
 	.trip_max_temp	= 120000,
+	.valid_bit = BIT(14),
+	.last_temp_resolution = 9,
 };
 
 static const struct reg_field tsens_v1_regfields[MAX_REGFIELDS] = {
diff --git a/drivers/thermal/qcom/tsens-v2.c b/drivers/thermal/qcom/tsens-v2.c
index 8d9698ea3ec4..d39d3a2923a3 100644
--- a/drivers/thermal/qcom/tsens-v2.c
+++ b/drivers/thermal/qcom/tsens-v2.c
@@ -56,6 +56,8 @@ static struct tsens_features tsens_v2_feat = {
 	.max_sensors	= 16,
 	.trip_min_temp	= -40000,
 	.trip_max_temp	= 120000,
+	.valid_bit = BIT(21),
+	.last_temp_resolution = 11,
 };
 
 static struct tsens_features ipq8074_feat = {
@@ -67,6 +69,8 @@ static struct tsens_features ipq8074_feat = {
 	.max_sensors	= 16,
 	.trip_min_temp	= 0,
 	.trip_max_temp	= 204000,
+	.valid_bit = BIT(21),
+	.last_temp_resolution = 11,
 };
 
 static struct tsens_features ipq5332_feat = {
@@ -78,6 +82,8 @@ static struct tsens_features ipq5332_feat = {
 	.max_sensors	= 16,
 	.trip_min_temp	= 0,
 	.trip_max_temp	= 204000,
+	.valid_bit = BIT(21),
+	.last_temp_resolution = 11,
 };
 
 static const struct reg_field tsens_v2_regfields[MAX_REGFIELDS] = {
diff --git a/drivers/thermal/qcom/tsens.c b/drivers/thermal/qcom/tsens.c
index a2422ebee816..1a7324afe321 100644
--- a/drivers/thermal/qcom/tsens.c
+++ b/drivers/thermal/qcom/tsens.c
@@ -315,10 +315,64 @@ static inline int code_to_degc(u32 adc_code, const struct tsens_sensor *s)
 	return degc;
 }
 
+/**
+ * tsens_read_temp - Retrieve temperature readings from the hardware.
+ * @s:     Pointer to sensor struct
+ * @field: Index into regmap_field array pointing to temperature data
+ * @temp: temperature in deciCelsius to be read from hardware
+ *
+ * This function handles temperature returned in ADC code or deciCelsius
+ * depending on IP version.
+ *
+ * Return: 0 on success, a negative errno will be returned in error cases
+ */
+static int tsens_read_temp(const struct tsens_sensor *s, int field, int *temp)
+{
+	struct tsens_priv *priv = s->priv;
+	int temp_val[MAX_READ_RETRY] = {0};
+	u32 status = 0;
+	int ret;
+
+	for (int i = 0; i < MAX_READ_RETRY; i++) {
+		ret = regmap_read(priv->tm_map, priv->fields[field].reg, &status);
+		if (ret)
+			return ret;
+
+		/* VER_0 doesn't have VALID bit */
+		if (!priv->rf[VALID_0 + s->hw_id]) {
+			*temp = status & priv->feat->last_temp_mask;
+			return 0;
+		}
+
+		temp_val[i] = status & priv->feat->last_temp_mask;
+
+		if (status & priv->feat->valid_bit) {
+			*temp = temp_val[i];
+			return 0;
+		}
+	}
+
+	/* As per the HW guidelines, if none of the attempts observe a
+	 * valid sample, a stable fallback value must be returned. If the
+	 * first and second samples match, the second value is returned;
+	 * otherwise, if the second and third samples match, the third
+	 * value is returned.
+	 */
+	if (temp_val[0] == temp_val[1])
+		*temp = temp_val[1];
+	else if (temp_val[1] == temp_val[2])
+		*temp = temp_val[2];
+	else
+		return -EAGAIN;
+
+	return ret;
+}
+
 /**
  * tsens_hw_to_mC - Return sign-extended temperature in mCelsius.
  * @s:     Pointer to sensor struct
  * @field: Index into regmap_field array pointing to temperature data
+ * @temp: temperature in milliCelsius to be read from hardware
  *
  * This function handles temperature returned in ADC code or deciCelsius
  * depending on IP version.
@@ -326,19 +380,12 @@ static inline int code_to_degc(u32 adc_code, const struct tsens_sensor *s)
  * Return: Temperature in milliCelsius on success, a negative errno will
  * be returned in error cases
  */
-static int tsens_hw_to_mC(const struct tsens_sensor *s, int field)
+static int tsens_hw_to_mC(const struct tsens_sensor *s, int temp)
 {
 	struct tsens_priv *priv = s->priv;
 	u32 resolution;
-	u32 temp = 0;
-	int ret;
-
-	resolution = priv->fields[LAST_TEMP_0].msb -
-		priv->fields[LAST_TEMP_0].lsb;
 
-	ret = regmap_field_read(priv->rf[field], &temp);
-	if (ret)
-		return ret;
+	resolution = priv->feat->last_temp_resolution;
 
 	/* Convert temperature from ADC code to milliCelsius */
 	if (priv->feat->adc)
@@ -514,8 +561,12 @@ static int tsens_read_irq_state(struct tsens_priv *priv, u32 hw_id,
 					&d->crit_irq_mask);
 		if (ret)
 			return ret;
-
-		d->crit_thresh = tsens_hw_to_mC(s, CRIT_THRESH_0 + hw_id);
+		ret = regmap_field_read(priv->rf[CRIT_THRESH_0 + hw_id], &d->crit_thresh);
+		if (ret)
+			return ret;
+		d->crit_thresh = tsens_hw_to_mC(s, d->crit_thresh);
+		if (ret)
+			return ret;
 	} else {
 		/* No mask register on older TSENS */
 		d->up_irq_mask = 0;
@@ -524,9 +575,14 @@ static int tsens_read_irq_state(struct tsens_priv *priv, u32 hw_id,
 		d->crit_irq_mask = 0;
 		d->crit_thresh = 0;
 	}
-
-	d->up_thresh  = tsens_hw_to_mC(s, UP_THRESH_0 + hw_id);
-	d->low_thresh = tsens_hw_to_mC(s, LOW_THRESH_0 + hw_id);
+	ret = regmap_field_read(priv->rf[UP_THRESH_0 + hw_id], &d->up_thresh);
+	if (ret)
+		return ret;
+	d->up_thresh = tsens_hw_to_mC(s, d->up_thresh);
+	ret = regmap_field_read(priv->rf[LOW_THRESH_0 + hw_id], &d->low_thresh);
+	if (ret)
+		return ret;
+	d->low_thresh = tsens_hw_to_mC(s, d->low_thresh);
 
 	dev_dbg(priv->dev, "[%u] %s%s: status(%u|%u|%u) | clr(%u|%u|%u) | mask(%u|%u|%u)\n",
 		hw_id, __func__,
@@ -750,33 +806,16 @@ static void tsens_disable_irq(struct tsens_priv *priv)
 
 int get_temp_tsens_valid(const struct tsens_sensor *s, int *temp)
 {
-	struct tsens_priv *priv = s->priv;
+	int ret;
 	int hw_id = s->hw_id;
 	u32 temp_idx = LAST_TEMP_0 + hw_id;
-	u32 valid_idx = VALID_0 + hw_id;
-	u32 valid;
-	int ret;
 
-	/* VER_0 doesn't have VALID bit */
-	if (tsens_version(priv) == VER_0)
-		goto get_temp;
+	ret = tsens_read_temp(s, temp_idx, temp);
 
-	/* Valid bit is 0 for 6 AHB clock cycles.
-	 * At 19.2MHz, 1 AHB clock is ~60ns.
-	 * We should enter this loop very, very rarely.
-	 * Wait 1 us since it's the min of poll_timeout macro.
-	 * Old value was 400 ns.
-	 */
-	ret = regmap_field_read_poll_timeout(priv->rf[valid_idx], valid,
-					     valid, 1, 20 * USEC_PER_MSEC);
-	if (ret)
-		return ret;
-
-get_temp:
-	/* Valid bit is set, OK to read the temperature */
-	*temp = tsens_hw_to_mC(s, temp_idx);
+	if (!ret)
+		*temp = tsens_hw_to_mC(s, *temp);
 
-	return 0;
+		return ret;
 }
 
 int get_temp_common(const struct tsens_sensor *s, int *temp)
@@ -1065,6 +1104,9 @@ int __init init_common(struct tsens_priv *priv)
 		regmap_field_write(priv->rf[CC_MON_MASK], 1);
 	}
 
+	priv->feat->last_temp_mask =
+			GENMASK(priv->feat->last_temp_resolution, 0);
+
 	spin_lock_init(&priv->ul_lock);
 
 	/* VER_0 interrupt doesn't need to be enabled */
diff --git a/drivers/thermal/qcom/tsens.h b/drivers/thermal/qcom/tsens.h
index 2a7afa4c899b..e56b6f29621b 100644
--- a/drivers/thermal/qcom/tsens.h
+++ b/drivers/thermal/qcom/tsens.h
@@ -21,6 +21,7 @@
 #define THRESHOLD_MIN_ADC_CODE	0x0
 
 #define MAX_SENSORS 16
+#define MAX_READ_RETRY 3
 
 #include <linux/interrupt.h>
 #include <linux/thermal.h>
@@ -511,6 +512,9 @@ enum regfield_ids {
  * @max_sensors: maximum sensors supported by this version of the IP
  * @trip_min_temp: minimum trip temperature supported by this version of the IP
  * @trip_max_temp: maximum trip temperature supported by this version of the IP
+ * @valid_bit: validate if read temperature is valid or not?
+ * @last_temp_mask: mask register for last temperature
+ * @last_temp_resolution: last temperarure sign bit resolution
  */
 struct tsens_features {
 	unsigned int ver_major;
@@ -522,6 +526,9 @@ struct tsens_features {
 	unsigned int max_sensors;
 	int trip_min_temp;
 	int trip_max_temp;
+	int valid_bit;
+	int last_temp_mask;
+	u32 last_temp_resolution;
 };
 
 /**
-- 
2.43.0