linux-kernel - [PATCH 6/8] rtc: isl12022: trigger battery level detection during probe

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Message-Id: <20230612113059.247275-7-linux@rasmusvillemoes.dk>
Date:   Mon, 12 Jun 2023 13:30:56 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-rtc@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 6/8] rtc: isl12022: trigger battery level detection during probe

Since the meaning of the SR_LBAT85 and SR_LBAT75 bits are different in
battery backup mode, they may very well be set after power on, and
stay set for up to a minute (i.e. until the battery detection in VDD
mode happens when the seconds counter hits 59). This would mean that
userspace doing a ioctl(RTC_VL_READ) early on could get a false
positive.

The battery level detection can also be triggered by explicitly
writing a 1 to the TSE bit in the BETA register. Do that once during
boot (well, probe), and emit a single warning to the kernel log if the
battery is already low.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 drivers/rtc/rtc-isl12022.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-isl12022.c b/drivers/rtc/rtc-isl12022.c
index 1b6659a9b33a..690dbb446d1a 100644
--- a/drivers/rtc/rtc-isl12022.c
+++ b/drivers/rtc/rtc-isl12022.c
@@ -280,8 +280,25 @@ static void isl12022_set_trip_levels(struct device *dev)
 	mask = ISL12022_REG_VB85_MASK | ISL12022_REG_VB75_MASK;
 
 	ret = regmap_update_bits(regmap, ISL12022_REG_PWR_VBAT, mask, val);
-	if (ret)
+	if (ret) {
 		dev_warn(dev, "unable to set battery alarm levels: %d\n", ret);
+		return;
+	}
+
+	ret = regmap_write_bits(regmap, ISL12022_REG_BETA,
+				ISL12022_BETA_TSE, ISL12022_BETA_TSE);
+	if (ret) {
+		dev_warn(dev, "unable to trigger battery level detection: %d\n", ret);
+		return;
+	}
+
+	ret = isl12022_read_sr(regmap);
+	if (ret < 0) {
+		dev_warn(dev, "unable to read status register: %d\n", ret);
+	} else if (ret & (ISL12022_SR_LBAT85 | ISL12022_SR_LBAT75)) {
+		dev_warn(dev, "battery voltage is below %u%%\n",
+			 (ret & ISL12022_SR_LBAT75) ? 75 : 85);
+	}
 }
 
 static int isl12022_probe(struct i2c_client *client)
-- 
2.37.2