linux-kernel - [PATCH v4 13/17] rtc: pcf2127: adapt time/date registers write sequence for PCF2131

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Message-Id: <20230622145800.2442116-14-hugo@hugovil.com>
Date:   Thu, 22 Jun 2023 10:57:56 -0400
From:   Hugo Villeneuve <hugo@...ovil.com>
To:     a.zummo@...ertech.it, alexandre.belloni@...tlin.com,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org
Cc:     linux-rtc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, hugo@...ovil.com,
        Hugo Villeneuve <hvilleneuve@...onoff.com>
Subject: [PATCH v4 13/17] rtc: pcf2127: adapt time/date registers write sequence for PCF2131

From: Hugo Villeneuve <hvilleneuve@...onoff.com>

The sequence for updating the time/date registers is slightly
different between PCF2127/29 and PCF2131.

For PCF2127/29, during write operations, the time counting
circuits (memory locations 03h through 09h) are automatically blocked.

For PCF2131, time/date registers write access requires setting the
STOP bit and sending the clear prescaler instruction (CPR). STOP then
needs to be released once write operation is completed.

Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
---
 drivers/rtc/rtc-pcf2127.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c
index 2eef65232417..3b8718aaadd7 100644
--- a/drivers/rtc/rtc-pcf2127.c
+++ b/drivers/rtc/rtc-pcf2127.c
@@ -33,6 +33,7 @@
 #define PCF2127_REG_CTRL1		0x00
 #define PCF2127_BIT_CTRL1_POR_OVRD		BIT(3)
 #define PCF2127_BIT_CTRL1_TSF1			BIT(4)
+#define PCF2127_BIT_CTRL1_STOP			BIT(5)
 /* Control register 2 */
 #define PCF2127_REG_CTRL2		0x01
 #define PCF2127_BIT_CTRL2_AIE			BIT(1)
@@ -280,13 +281,45 @@ static int pcf2127_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	/* year */
 	buf[i++] = bin2bcd(tm->tm_year - 100);
 
-	/* write register's data */
+	/* Write access to time registers:
+	 * PCF2127/29: no special action required.
+	 * PCF2131:    requires setting the STOP and CPR bits. STOP bit needs to
+	 *             be cleared after time registers are updated.
+	 */
+	if (pcf2127->cfg->type == PCF2131) {
+		err = regmap_update_bits(pcf2127->regmap, PCF2127_REG_CTRL1,
+					 PCF2127_BIT_CTRL1_STOP,
+					 PCF2127_BIT_CTRL1_STOP);
+		if (err) {
+			dev_dbg(dev, "setting STOP bit failed\n");
+			return err;
+		}
+
+		err = regmap_write(pcf2127->regmap, PCF2131_REG_SR_RESET,
+				   PCF2131_SR_RESET_CPR_CMD);
+		if (err) {
+			dev_dbg(dev, "sending CPR cmd failed\n");
+			return err;
+		}
+	}
+
+	/* write time register's data */
 	err = regmap_bulk_write(pcf2127->regmap, pcf2127->cfg->reg_time_base, buf, i);
 	if (err) {
 		dev_dbg(dev, "%s: err=%d", __func__, err);
 		return err;
 	}
 
+	if (pcf2127->cfg->type == PCF2131) {
+		/* Clear STOP bit (PCF2131 only) after write is completed. */
+		err = regmap_update_bits(pcf2127->regmap, PCF2127_REG_CTRL1,
+					 PCF2127_BIT_CTRL1_STOP, 0);
+		if (err) {
+			dev_dbg(dev, "clearing STOP bit failed\n");
+			return err;
+		}
+	}
+
 	return 0;
 }
 
-- 
2.30.2