linux-kernel - [PATCH v2 2/2] drivers: thermal: tsens: add timeout to get_tem_tsens

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Date:   Tue,  7 Sep 2021 23:25:43 +0200
From:   Ansuel Smith <ansuelsmth@...il.com>
To:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Amit Kucheria <amitk@...nel.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Ansuel Smith <ansuelsmth@...il.com>
Subject: [PATCH v2 2/2] drivers: thermal: tsens: add timeout to get_tem_tsens_valid

The function can loop and lock the system if for whatever reason the bit
for the target sensor is NEVER valid. This is the case if a sensor is
disabled by the factory and the valid bit is never reported as actually
valid. Add a timeout check and exit if a timeout occurs. As this is
a very rare condition, handle the timeout only if the first read fails.
While at it also rework the function to improve readability.

Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>
---
 drivers/thermal/qcom/tsens.c | 40 +++++++++++++++++++++++-------------
 1 file changed, 26 insertions(+), 14 deletions(-)

diff --git a/drivers/thermal/qcom/tsens.c b/drivers/thermal/qcom/tsens.c
index b1162e566a70..1ff244176beb 100644
--- a/drivers/thermal/qcom/tsens.c
+++ b/drivers/thermal/qcom/tsens.c
@@ -599,26 +599,38 @@ int get_temp_tsens_valid(const struct tsens_sensor *s, int *temp)
 	int hw_id = s->hw_id;
 	u32 temp_idx = LAST_TEMP_0 + hw_id;
 	u32 valid_idx = VALID_0 + hw_id;
+	unsigned long timeout;
 	u32 valid;
 	int ret;
 
 	/* VER_0 doesn't have VALID bit */
-	if (tsens_version(priv) >= VER_0_1) {
+	if (tsens_version(priv) == VER_0)
+		goto get_temp;
+
+	ret = regmap_field_read(priv->rf[valid_idx], &valid);
+	if (ret || valid)
+		goto check_valid;
+
+	timeout = jiffies + msecs_to_jiffies(20);
+	do {
+		/* 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.
+		 */
+		ndelay(400);
 		ret = regmap_field_read(priv->rf[valid_idx], &valid);
-		if (ret)
-			return ret;
-		while (!valid) {
-			/* 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.
-			 */
-			ndelay(400);
-			ret = regmap_field_read(priv->rf[valid_idx], &valid);
-			if (ret)
-				return ret;
-		}
-	}
+		if (ret || valid)
+			goto check_valid;
+	} while (time_before(jiffies, timeout));
+
+	return -ETIMEDOUT;
+
+check_valid:
+	/* Check ret of valid bit read */
+	if (ret)
+		return ret;
 
+get_temp:
 	/* Valid bit is set, OK to read the temperature */
 	*temp = tsens_hw_to_mC(s, temp_idx);
 
-- 
2.32.0