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

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Message-Id: <20210905174708.4605-2-ansuelsmth@gmail.com>
Date:   Sun,  5 Sep 2021 19:47:08 +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 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.

Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>
---
 drivers/thermal/qcom/tsens.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/thermal/qcom/tsens.c b/drivers/thermal/qcom/tsens.c
index b1162e566a70..38afde1a599f 100644
--- a/drivers/thermal/qcom/tsens.c
+++ b/drivers/thermal/qcom/tsens.c
@@ -599,6 +599,7 @@ 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;
 
@@ -607,13 +608,21 @@ int get_temp_tsens_valid(const struct tsens_sensor *s, int *temp)
 		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 (!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 (valid || ret)
+					break;
+			} while (!(ret = time_after_eq(jiffies, timeout)));
+
 			if (ret)
 				return ret;
 		}
-- 
2.32.0