linux-kernel - [PATCH v2 0/2] rtc: pcf2127: proper initialization after power loss

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Date:   Wed, 13 Jan 2021 12:27:40 +0100
From:   Philipp Rosenberger <p.rosenberger@...bus.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     p.rosenberger@...bus.com, dan.carpenter@...cle.com,
        u.kleine-koenig@...gutronix.de, biwen.li@....com, lvb@...hos.com,
        bruno.thomsen@...il.com, l.sanfilippo@...bus.com,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/2] rtc: pcf2127: proper initialization after power loss

If the PCF2127/2129 loses power it needs some initialization to work
correctly. A bootloader/firmware might do this. If not we should do this
in the driver.

Changes for v2:
- make commit log and comments more clear
- check if PORO was really disabled

Philipp Rosenberger (2):
  rtc: pcf2127: Disable Power-On Reset Override
  rtc: pcf2127: Run a OTP refresh if not done before

 drivers/rtc/rtc-pcf2127.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

Interdiff against v1:
diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c
index f012b989f2f2..ca56dba64e79 100644
--- a/drivers/rtc/rtc-pcf2127.c
+++ b/drivers/rtc/rtc-pcf2127.c
@@ -26,6 +26,7 @@
 
 /* Control register 1 */
 #define PCF2127_REG_CTRL1		0x00
+#define PCF2127_BIT_CTRL1_POR_OVRD		BIT(3)
 #define PCF2127_BIT_CTRL1_TSF1			BIT(4)
 /* Control register 2 */
 #define PCF2127_REG_CTRL2		0x01
@@ -616,18 +617,27 @@ static int pcf2127_probe(struct device *dev, struct regmap *regmap,
 	}
 
 	/*
-	 * Disable the Power-On Reset Override facility to start normal
-	 * operation. If the operation should fail, just move on. The RTC should
-	 * work fine, but functions like watchdog and alarm interrupts might
-	 * not work.
+	 * The "Power-On Reset Override" facility prevents the RTC to do a reset
+	 * after power on. For normal operation the PORO must be disabled.
 	 */
-	ret = regmap_clear_bits(pcf2127->regmap, PCF2127_REG_CTRL1,
+	regmap_clear_bits(pcf2127->regmap, PCF2127_REG_CTRL1,
 				PCF2127_BIT_CTRL1_POR_OVRD);
-	if (ret) {
+	/*
+	 * If the PORO can't be disabled, just move on. The RTC should
+	 * work fine, but functions like watchdog and alarm interrupts might
+	 * not work. There will be no interrupt generated on the interrupt pin.
+	 */
+	ret = regmap_test_bits(pcf2127->regmap, PCF2127_REG_CTRL1, PCF2127_BIT_CTRL1_POR_OVRD);
+	if (ret <= 0) {
 		dev_err(dev, "%s: can't disable PORO (ctrl1).\n", __func__);
 		dev_warn(dev, "Watchdog and alarm functions might not work properly\n");
 	}
 
+	/*
+	 * Set the OTP refresh bit unconditionally. If an OTP refresh was
+	 * already done the bit is already set and will not rerun the refresh
+	 * operation.
+	 */
 	ret = regmap_set_bits(pcf2127->regmap, PCF2127_REG_CLKOUT,
 			      PCF2127_BIT_CLKOUT_OTPR);
 	if (ret < 0) {
-- 
2.29.2