rtc: pm8xxx: add support for nvmem offset

On many Qualcomm platforms the PMIC RTC control and time registers are
read-only so that the RTC time can not be updated. Instead an offset
needs be stored in some machine-specific non-volatile memory, which the
driver can take into account.

Add support for storing a 32-bit offset from the Epoch in an nvmem cell
so that the RTC time can be set on such platforms.

Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20230202155448.6715-18-johan+linaro@kernel.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-pm8xxx.c

@@ -1,8 +1,13 @@
 // SPDX-License-Identifier: GPL-2.0-only
-/* Copyright (c) 2010-2011, Code Aurora Forum. All rights reserved.
+/*
+ * pm8xxx RTC driver
+ *
+ * Copyright (c) 2010-2011, Code Aurora Forum. All rights reserved.
+ * Copyright (c) 2023, Linaro Limited
  */
 #include <linux/of.h>
 #include <linux/module.h>
+#include <linux/nvmem-consumer.h>
 #include <linux/init.h>
 #include <linux/rtc.h>
 #include <linux/platform_device.h>
@@ -49,6 +54,8 @@ struct pm8xxx_rtc_regs {
  * @alarm_irq:		alarm irq number
  * @regs:		register description
  * @dev:		device structure
+ * @nvmem_cell:		nvmem cell for offset
+ * @offset:		offset from epoch in seconds
  */
 struct pm8xxx_rtc {
 	struct rtc_device *rtc;
@@ -57,8 +64,60 @@ struct pm8xxx_rtc {
 	int alarm_irq;
 	const struct pm8xxx_rtc_regs *regs;
 	struct device *dev;
+	struct nvmem_cell *nvmem_cell;
+	u32 offset;
 };
 
+static int pm8xxx_rtc_read_nvmem_offset(struct pm8xxx_rtc *rtc_dd)
+{
+	size_t len;
+	void *buf;
+	int rc;
+
+	buf = nvmem_cell_read(rtc_dd->nvmem_cell, &len);
+	if (IS_ERR(buf)) {
+		rc = PTR_ERR(buf);
+		dev_dbg(rtc_dd->dev, "failed to read nvmem offset: %d\n", rc);
+		return rc;
+	}
+
+	if (len != sizeof(u32)) {
+		dev_dbg(rtc_dd->dev, "unexpected nvmem cell size %zu\n", len);
+		kfree(buf);
+		return -EINVAL;
+	}
+
+	rtc_dd->offset = get_unaligned_le32(buf);
+
+	kfree(buf);
+
+	return 0;
+}
+
+static int pm8xxx_rtc_write_nvmem_offset(struct pm8xxx_rtc *rtc_dd, u32 offset)
+{
+	u8 buf[sizeof(u32)];
+	int rc;
+
+	put_unaligned_le32(offset, buf);
+
+	rc = nvmem_cell_write(rtc_dd->nvmem_cell, buf, sizeof(buf));
+	if (rc < 0) {
+		dev_dbg(rtc_dd->dev, "failed to write nvmem offset: %d\n", rc);
+		return rc;
+	}
+
+	return 0;
+}
+
+static int pm8xxx_rtc_read_offset(struct pm8xxx_rtc *rtc_dd)
+{
+	if (!rtc_dd->nvmem_cell)
+		return 0;
+
+	return pm8xxx_rtc_read_nvmem_offset(rtc_dd);
+}
+
 static int pm8xxx_rtc_read_raw(struct pm8xxx_rtc *rtc_dd, u32 *secs)
 {
 	const struct pm8xxx_rtc_regs *regs = rtc_dd->regs;
@@ -90,6 +149,33 @@ static int pm8xxx_rtc_read_raw(struct pm8xxx_rtc *rtc_dd, u32 *secs)
 	return 0;
 }
 
+static int pm8xxx_rtc_update_offset(struct pm8xxx_rtc *rtc_dd, u32 secs)
+{
+	u32 raw_secs;
+	u32 offset;
+	int rc;
+
+	if (!rtc_dd->nvmem_cell)
+		return -ENODEV;
+
+	rc = pm8xxx_rtc_read_raw(rtc_dd, &raw_secs);
+	if (rc)
+		return rc;
+
+	offset = secs - raw_secs;
+
+	if (offset == rtc_dd->offset)
+		return 0;
+
+	rc = pm8xxx_rtc_write_nvmem_offset(rtc_dd, offset);
+	if (rc)
+		return rc;
+
+	rtc_dd->offset = offset;
+
+	return 0;
+}
+
 /*
  * Steps to write the RTC registers.
  * 1. Disable alarm if enabled.
@@ -99,23 +185,15 @@ static int pm8xxx_rtc_read_raw(struct pm8xxx_rtc *rtc_dd, u32 *secs)
  * 5. Enable rtc if disabled in step 2.
  * 6. Enable alarm if disabled in step 1.
  */
-static int pm8xxx_rtc_set_time(struct device *dev, struct rtc_time *tm)
+static int __pm8xxx_rtc_set_time(struct pm8xxx_rtc *rtc_dd, u32 secs)
 {
-	struct pm8xxx_rtc *rtc_dd = dev_get_drvdata(dev);
 	const struct pm8xxx_rtc_regs *regs = rtc_dd->regs;
 	u8 value[NUM_8_BIT_RTC_REGS];
 	bool alarm_enabled;
-	u32 secs;
 	int rc;
 
-	if (!rtc_dd->allow_set_time)
-		return -ENODEV;
-
-	secs = rtc_tm_to_time64(tm);
 	put_unaligned_le32(secs, value);
 
-	dev_dbg(dev, "set time: %ptRd %ptRt (%u)\n", tm, tm, secs);
-
 	rc = regmap_update_bits_check(rtc_dd->regmap, regs->alarm_ctrl,
 				      regs->alarm_en, 0, &alarm_enabled);
 	if (rc)
@@ -158,6 +236,27 @@ static int pm8xxx_rtc_set_time(struct device *dev, struct rtc_time *tm)
 	return 0;
 }
 
+static int pm8xxx_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct pm8xxx_rtc *rtc_dd = dev_get_drvdata(dev);
+	u32 secs;
+	int rc;
+
+	secs = rtc_tm_to_time64(tm);
+
+	if (rtc_dd->allow_set_time)
+		rc = __pm8xxx_rtc_set_time(rtc_dd, secs);
+	else
+		rc = pm8xxx_rtc_update_offset(rtc_dd, secs);
+
+	if (rc)
+		return rc;
+
+	dev_dbg(dev, "set time: %ptRd %ptRt (%u + %u)\n", tm, tm,
+			secs - rtc_dd->offset, rtc_dd->offset);
+	return 0;
+}
+
 static int pm8xxx_rtc_read_time(struct device *dev, struct rtc_time *tm)
 {
 	struct pm8xxx_rtc *rtc_dd = dev_get_drvdata(dev);
@@ -168,10 +267,11 @@ static int pm8xxx_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	if (rc)
 		return rc;
 
+	secs += rtc_dd->offset;
 	rtc_time64_to_tm(secs, tm);
 
-	dev_dbg(dev, "read time: %ptRd %ptRt (%u)\n", tm, tm, secs);
-
+	dev_dbg(dev, "read time: %ptRd %ptRt (%u + %u)\n", tm, tm,
+			secs - rtc_dd->offset, rtc_dd->offset);
 	return 0;
 }
 
@@ -184,6 +284,7 @@ static int pm8xxx_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
 	int rc;
 
 	secs = rtc_tm_to_time64(&alarm->time);
+	secs -= rtc_dd->offset;
 	put_unaligned_le32(secs, value);
 
 	rc = regmap_update_bits(rtc_dd->regmap, regs->alarm_ctrl,
@@ -223,6 +324,7 @@ static int pm8xxx_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
 		return rc;
 
 	secs = get_unaligned_le32(value);
+	secs += rtc_dd->offset;
 	rtc_time64_to_tm(secs, &alarm->time);
 
 	rc = regmap_read(rtc_dd->regmap, regs->alarm_ctrl, &ctrl_reg);
@@ -378,9 +480,23 @@ static int pm8xxx_rtc_probe(struct platform_device *pdev)
 	rtc_dd->allow_set_time = of_property_read_bool(pdev->dev.of_node,
 						      "allow-set-time");
 
+	rtc_dd->nvmem_cell = devm_nvmem_cell_get(&pdev->dev, "offset");
+	if (IS_ERR(rtc_dd->nvmem_cell)) {
+		rc = PTR_ERR(rtc_dd->nvmem_cell);
+		if (rc != -ENOENT)
+			return rc;
+		rtc_dd->nvmem_cell = NULL;
+	}
+
 	rtc_dd->regs = match->data;
 	rtc_dd->dev = &pdev->dev;
 
+	if (!rtc_dd->allow_set_time) {
+		rc = pm8xxx_rtc_read_offset(rtc_dd);
+		if (rc)
+			return rc;
+	}
+
 	rc = pm8xxx_rtc_enable(rtc_dd);
 	if (rc)
 		return rc;
@@ -435,3 +551,4 @@ MODULE_ALIAS("platform:rtc-pm8xxx");
 MODULE_DESCRIPTION("PMIC8xxx RTC driver");
 MODULE_LICENSE("GPL v2");
 MODULE_AUTHOR("Anirudh Ghayal <aghayal@codeaurora.org>");
+MODULE_AUTHOR("Johan Hovold <johan@kernel.org>");