[PATCH v10 3/3] rtc: Add Raspberry Pi 5 RTC driver

[Sander Speetjens <sander.speetjens@gmail.com>]

Upstreaming the downstream Raspberry Pi 5 RTC driver.
This driver supports the custom DA9091,
which is accessed through the firmware mailbox.

Based on code originally written by Jonathan Bell <jonathan@raspberrypi.com>
and Dom Cobley <popcornmix@gmail.com>

Signed-off-by: Sander Speetjens <sander.speetjens@gmail.com>
---
V9 -> V10:
- Fix sign-off-by
- Change enum to defines
- Change comment in firmware

V8 -> V9:
- Fix whitespace in Kconfig
- Move RTC regs to firmware header
- Add a warn when getting the min or max charging values fails
- Remove the unused return value of set charge voltage

V7 -> V8:
- Fix whitespacing errors
- Use of_machine_is_compatible instead of strncmp

V6 -> V7:
- Move from u32 array to struct
- Fix encapsulation as mentioned by sashiko-bot

V5 -> V6:
- Add MODULE_ALIAS, as mentioned by sashiko-bot
- Encapsulate the mailbox data in le32_to_cpu or cpu_to_le32, as
  mentioned by sashiko-bot. For good practice

V4 -> V5: No changes

V3 -> V4:
- Fix Kconfig depends that disallows having Raspberrypi
firmware built as a module while the rtc driver is built in
- Remove sysfs
- Add limits from firmware properties and check in rpi_rtc_set_charge_voltage

V2 -> V3:
- Move platform check to firmware and abort before registering
a platform device if on another platform
- Add a dependency on the Raspberry Pi firmware to Kconfig
- Check return value of devm_device_init_wakeup
- Fix property name

V1 -> V2:
Instead of the original driver, which was directly bound to the device tree.
This driver is bound to the Raspberry Pi firmware device by creating
a child device in the firmware driver probe function.
The child device is then bound to this driver,
which uses the firmware mailbox to access the RTC.

A couple of minor changes have been made to the driver since it was originally written, including:
- Checking if the model is a Raspberry Pi 5, as the RTC is only present on that model.
- Using the new devm_rpi_firmware_get() and devm_init_wakeup() helper to get the firmware device and avoid leaking memory.
- Using millivolts instead of microvolts for the trickle charge voltage, to match the RTC standard.
- Instead of setting the trickle charge voltage to 0 to disable trickle charging, the property is now optional. If the property is not present, trickle charging is disabled, per the RTC standard.
- Renaming the driver dt match compatible to "raspberrypi,firmware-rtc" to match the other firmware bindings.
- Renaming the driver name to "raspberrypi-rtc" to match the other firmware drivers.

 drivers/firmware/raspberrypi.c             |  24 ++
 drivers/rtc/Kconfig                        |  12 +
 drivers/rtc/Makefile                       |   1 +
 drivers/rtc/rtc-raspberrypi.c              | 276 +++++++++++++++++++++
 include/soc/bcm2835/raspberrypi-firmware.h |   2 +
 5 files changed, 315 insertions(+)
 create mode 100644 drivers/rtc/rtc-raspberrypi.c

diff --git a/drivers/firmware/raspberrypi.c b/drivers/firmware/raspberrypi.c
index 0aa322e9a2e7..f8c83c25eccc 100644
--- a/drivers/firmware/raspberrypi.c
+++ b/drivers/firmware/raspberrypi.c
@@ -24,6 +24,7 @@
 
 static struct platform_device *rpi_hwmon;
 static struct platform_device *rpi_clk;
+static struct platform_device *rpi_rtc;
 
 struct rpi_firmware {
 	struct mbox_client cl;
@@ -231,6 +232,26 @@ static void rpi_register_clk_driver(struct device *dev)
 						-1, NULL, 0);
 }
 
+static void rpi_register_rtc_driver(struct device *dev)
+{
+	struct device_node *firmware;
+
+	// Check if our model of Raspberry Pi board is from the 5th gen
+	// as the RTC is only present on that model.
+	if (!of_machine_is_compatible("brcm,bcm2712"))
+		return;
+
+	firmware = of_get_compatible_child(dev->of_node,
+					   "raspberrypi,firmware-rtc");
+	if (firmware) {
+		of_node_put(firmware);
+		return;
+	}
+
+	rpi_rtc = platform_device_register_data(dev, "raspberrypi-rtc",
+						-1, NULL, 0);
+}
+
 unsigned int rpi_firmware_clk_get_max_rate(struct rpi_firmware *fw, unsigned int id)
 {
 	struct rpi_firmware_clk_rate_request msg =
@@ -305,6 +326,7 @@ static int rpi_firmware_probe(struct platform_device *pdev)
 	rpi_firmware_print_firmware_revision(fw);
 	rpi_register_hwmon_driver(dev, fw);
 	rpi_register_clk_driver(dev);
+	rpi_register_rtc_driver(dev);
 
 	return 0;
 }
@@ -327,6 +349,8 @@ static void rpi_firmware_remove(struct platform_device *pdev)
 	rpi_hwmon = NULL;
 	platform_device_unregister(rpi_clk);
 	rpi_clk = NULL;
+	platform_device_unregister(rpi_rtc);
+	rpi_rtc = NULL;
 
 	rpi_firmware_put(fw);
 }
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 05b9233b9418..6dae4c069be2 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -1999,6 +1999,18 @@ config RTC_DRV_R7301
 	   This driver can also be built as a module. If so, the module
 	   will be called rtc-r7301.
 
+config RTC_DRV_RPI
+	tristate "Raspberry Pi RTC"
+	depends on RASPBERRYPI_FIRMWARE || (COMPILE_TEST && !RASPBERRYPI_FIRMWARE)
+	depends on ARCH_BRCMSTB || COMPILE_TEST
+	default ARCH_BRCMSTB
+	help
+		If you say yes here you get support for the RTC found on
+		Raspberry Pi devices.
+
+		This driver can also be built as a module. If so, the module
+		will be called rtc-raspberrypi.
+
 config RTC_DRV_STM32
 	tristate "STM32 RTC"
 	select REGMAP_MMIO
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 0347645b021f..46f1a0fc2416 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -144,6 +144,7 @@ obj-$(CONFIG_RTC_DRV_PS3)	+= rtc-ps3.o
 obj-$(CONFIG_RTC_DRV_PXA)	+= rtc-pxa.o
 obj-$(CONFIG_RTC_DRV_R7301)	+= rtc-r7301.o
 obj-$(CONFIG_RTC_DRV_R9701)	+= rtc-r9701.o
+obj-$(CONFIG_RTC_DRV_RPI)	+= rtc-raspberrypi.o
 obj-$(CONFIG_RTC_DRV_RC5T583)	+= rtc-rc5t583.o
 obj-$(CONFIG_RTC_DRV_RC5T619)	+= rtc-rc5t619.o
 obj-$(CONFIG_RTC_DRV_RK808)	+= rtc-rk808.o
diff --git a/drivers/rtc/rtc-raspberrypi.c b/drivers/rtc/rtc-raspberrypi.c
new file mode 100644
index 000000000000..0496851cfc30
--- /dev/null
+++ b/drivers/rtc/rtc-raspberrypi.c
@@ -0,0 +1,276 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
+/**
+ * rtc-raspberrypi.c
+ *
+ * RTC driver using firmware mailbox
+ * Supports battery backed RTC and wake alarms
+ *
+ * Based on rtc-meson-vrtc by Neil Armstrong
+ *
+ * Copyright (c) 2023, Raspberry Pi Ltd.
+ */
+
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/of.h>
+#include <soc/bcm2835/raspberrypi-firmware.h>
+
+#define	RTC_TIME 		0
+#define	RTC_ALARM		1
+#define	RTC_ALARM_PENDING	2
+#define	RTC_ALARM_ENABLE	3
+#define	RTC_BBAT_CHG_VOLTS	4
+#define	RTC_BBAT_CHG_VOLTS_MIN	5
+#define	RTC_BBAT_CHG_VOLTS_MAX	6
+#define	RTC_BBAT_VOLTS		7
+
+struct rpi_rtc_data {
+	struct rtc_device *rtc;
+	struct rpi_firmware *fw;
+	u32 bbat_vchg_millivolts;
+	u32 bbat_vchg_min_millivolts;
+	u32 bbat_vchg_max_millivolts;
+};
+
+struct rpi_rtc_reg {
+	__le32 reg;
+	__le32 val;
+} __packed;
+
+static int rpi_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rpi_rtc_data *vrtc = dev_get_drvdata(dev);
+	struct rpi_rtc_reg data = {
+		.reg = cpu_to_le32(RTC_TIME)
+	};
+	int err;
+
+	err = rpi_firmware_property(vrtc->fw, RPI_FIRMWARE_GET_RTC_REG,
+				    &data, sizeof(data));
+	rtc_time64_to_tm(le32_to_cpu(data.val), tm);
+	return err;
+}
+
+static int rpi_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rpi_rtc_data *vrtc = dev_get_drvdata(dev);
+	struct rpi_rtc_reg data = {
+		.reg = cpu_to_le32(RTC_TIME),
+		.val = cpu_to_le32(rtc_tm_to_time64(tm))
+	};
+
+	return rpi_firmware_property(vrtc->fw, RPI_FIRMWARE_SET_RTC_REG,
+				     &data, sizeof(data));
+}
+
+static int rpi_rtc_alarm_irq_is_enabled(struct device *dev, unsigned char *enabled)
+{
+	struct rpi_rtc_data *vrtc = dev_get_drvdata(dev);
+	struct rpi_rtc_reg data = {
+		.reg = cpu_to_le32(RTC_ALARM_ENABLE)
+	};
+	int err;
+
+	err = rpi_firmware_property(vrtc->fw, RPI_FIRMWARE_GET_RTC_REG,
+				    &data, sizeof(data));
+	*enabled = le32_to_cpu(data.val) & 0x1;
+	return err;
+}
+
+static int rpi_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct rpi_rtc_data *vrtc = dev_get_drvdata(dev);
+	struct rpi_rtc_reg data = {
+		.reg = cpu_to_le32(RTC_ALARM_ENABLE),
+		.val = cpu_to_le32(enabled)
+	};
+
+	return rpi_firmware_property(vrtc->fw, RPI_FIRMWARE_SET_RTC_REG,
+				     &data, sizeof(data));
+}
+
+static int rpi_rtc_alarm_clear_pending(struct device *dev)
+{
+	struct rpi_rtc_data *vrtc = dev_get_drvdata(dev);
+	struct rpi_rtc_reg data = {
+		.reg = cpu_to_le32(RTC_ALARM_PENDING),
+		.val = cpu_to_le32(1)
+	};
+
+	return rpi_firmware_property(vrtc->fw, RPI_FIRMWARE_SET_RTC_REG,
+				     &data, sizeof(data));
+}
+
+static int rpi_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct rpi_rtc_data *vrtc = dev_get_drvdata(dev);
+	struct rpi_rtc_reg data = {
+		.reg = cpu_to_le32(RTC_ALARM)
+	};
+	int err;
+
+	err = rpi_rtc_alarm_irq_is_enabled(dev, &alarm->enabled);
+	if (!err)
+		err = rpi_firmware_property(vrtc->fw, RPI_FIRMWARE_GET_RTC_REG,
+					    &data, sizeof(data));
+	rtc_time64_to_tm(le32_to_cpu(data.val), &alarm->time);
+
+	return err;
+}
+
+static int rpi_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct rpi_rtc_data *vrtc = dev_get_drvdata(dev);
+	struct rpi_rtc_reg data = {
+		.reg = cpu_to_le32(RTC_ALARM),
+		.val = cpu_to_le32(rtc_tm_to_time64(&alarm->time))
+	};
+	int err;
+
+	err = rpi_firmware_property(vrtc->fw, RPI_FIRMWARE_SET_RTC_REG,
+				    &data, sizeof(data));
+
+	if (!err)
+		err = rpi_rtc_alarm_irq_enable(dev, alarm->enabled);
+
+	return err;
+}
+
+static const struct rtc_class_ops rpi_rtc_ops = {
+	.read_time = rpi_rtc_read_time,
+	.set_time = rpi_rtc_set_time,
+	.read_alarm = rpi_rtc_read_alarm,
+	.set_alarm = rpi_rtc_set_alarm,
+	.alarm_irq_enable = rpi_rtc_alarm_irq_enable,
+};
+
+static void rpi_rtc_set_limits(struct device *dev)
+{
+	struct rpi_rtc_data *vrtc = dev_get_drvdata(dev);
+	struct rpi_rtc_reg data = {
+		.reg = cpu_to_le32(RTC_BBAT_CHG_VOLTS_MIN)
+	};
+
+	int err = rpi_firmware_property(vrtc->fw, RPI_FIRMWARE_GET_RTC_REG,
+					&data, sizeof(data));
+	if (!err)
+		vrtc->bbat_vchg_min_millivolts = le32_to_cpu(data.val) / 1000U;
+	else
+		dev_warn(dev, "failed to get minimum trickle charge voltage\n");
+
+	data.reg = cpu_to_le32(RTC_BBAT_CHG_VOLTS_MAX);
+	data.val = cpu_to_le32(0);
+	err = rpi_firmware_property(vrtc->fw, RPI_FIRMWARE_GET_RTC_REG,
+				    &data, sizeof(data));
+	if (!err)
+		vrtc->bbat_vchg_max_millivolts = le32_to_cpu(data.val) / 1000U;
+	else
+		dev_warn(dev, "failed to get maximum trickle charge voltage\n");
+}
+
+static void rpi_rtc_set_charge_voltage(struct device *dev)
+{
+	struct rpi_rtc_data *vrtc = dev_get_drvdata(dev);
+	struct rpi_rtc_reg data = {
+		.reg = cpu_to_le32(RTC_BBAT_CHG_VOLTS),
+		.val = cpu_to_le32(vrtc->bbat_vchg_millivolts * 1000U)
+	};
+	int err;
+
+	if (vrtc->bbat_vchg_millivolts != 0 &&
+	    (vrtc->bbat_vchg_millivolts < vrtc->bbat_vchg_min_millivolts ||
+	    vrtc->bbat_vchg_millivolts > vrtc->bbat_vchg_max_millivolts)) {
+		dev_warn(dev, "trickle charge voltage %umV is outside of the supported range (%umV - %umV)\n",
+			 vrtc->bbat_vchg_millivolts,
+			 vrtc->bbat_vchg_min_millivolts,
+			 vrtc->bbat_vchg_max_millivolts);
+		return;
+	}
+
+	err = rpi_firmware_property(vrtc->fw, RPI_FIRMWARE_SET_RTC_REG,
+				    &data, sizeof(data));
+
+	if (err)
+		dev_err(dev, "failed to set trickle charge voltage to %umV: %d\n",
+			vrtc->bbat_vchg_millivolts, err);
+	else if (vrtc->bbat_vchg_millivolts)
+		dev_info(dev, "trickle charging enabled at %umV\n",
+			 vrtc->bbat_vchg_millivolts);
+}
+
+static int rpi_rtc_probe(struct platform_device *pdev)
+{
+	struct rpi_rtc_data *vrtc;
+	struct device *dev = &pdev->dev;
+	struct rpi_firmware *firmware;
+	int ret;
+
+	// Get the firmware device from the parent device
+	firmware = devm_rpi_firmware_get(dev, dev->parent->of_node);
+
+	if (!firmware)
+		return -EPROBE_DEFER;
+
+	vrtc = devm_kzalloc(dev, sizeof(*vrtc), GFP_KERNEL);
+	if (!vrtc)
+		return -ENOMEM;
+
+	vrtc->fw = firmware;
+
+	ret = devm_device_init_wakeup(dev);
+	if (ret)
+		return ret;
+
+	platform_set_drvdata(pdev, vrtc);
+
+	vrtc->rtc = devm_rtc_allocate_device(dev);
+	if (IS_ERR(vrtc->rtc))
+		return PTR_ERR(vrtc->rtc);
+
+	vrtc->rtc->range_max = U32_MAX;           /* 2106-02-07 */
+
+	set_bit(RTC_FEATURE_ALARM_WAKEUP_ONLY, vrtc->rtc->features);
+	clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, vrtc->rtc->features);
+
+	vrtc->rtc->ops = &rpi_rtc_ops;
+
+	rpi_rtc_alarm_clear_pending(dev);
+
+	/*
+	 * The trickle-voltage property lives on the parent firmware node
+	 * because we deliberately do not create a DT child node just to
+	 * instantiate this driver (see DT maintainer guidance).
+	 * The firmware driver registers us as a platform device at runtime.
+	 */
+	vrtc->bbat_vchg_millivolts = 0;
+	of_property_read_u32(dev->parent->of_node, "trickle-voltage-millivolt",
+			     &vrtc->bbat_vchg_millivolts);
+
+	rpi_rtc_set_limits(dev);
+	rpi_rtc_set_charge_voltage(dev);
+
+	return devm_rtc_register_device(vrtc->rtc);
+}
+
+static const struct of_device_id rpi_rtc_dt_match[] = {
+	{ .compatible = "raspberrypi,firmware-rtc" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, rpi_rtc_dt_match);
+
+static struct platform_driver rpi_rtc_driver = {
+	.driver = {
+		.name = "raspberrypi-rtc",
+		.of_match_table = of_match_ptr(rpi_rtc_dt_match),
+	},
+	.probe = rpi_rtc_probe
+};
+
+module_platform_driver(rpi_rtc_driver);
+
+MODULE_AUTHOR("Jonathan Bell <jonathan@raspberrypi.com>");
+MODULE_AUTHOR("Sander Speetjens <sander.speetjens@gmail.com>");
+MODULE_DESCRIPTION("Raspberry Pi RTC driver");
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_ALIAS("platform:raspberrypi-rtc");
diff --git a/include/soc/bcm2835/raspberrypi-firmware.h b/include/soc/bcm2835/raspberrypi-firmware.h
index 975bef529854..e13994d8281c 100644
--- a/include/soc/bcm2835/raspberrypi-firmware.h
+++ b/include/soc/bcm2835/raspberrypi-firmware.h
@@ -75,6 +75,8 @@ enum rpi_firmware_property_tag {
 	RPI_FIRMWARE_GET_THROTTLED =                          0x00030046,
 	RPI_FIRMWARE_GET_CLOCK_MEASURED =                     0x00030047,
 	RPI_FIRMWARE_NOTIFY_REBOOT =                          0x00030048,
+	RPI_FIRMWARE_GET_RTC_REG =                            0x00030087,
+	RPI_FIRMWARE_SET_RTC_REG =                            0x00038087,
 	RPI_FIRMWARE_SET_CLOCK_STATE =                        0x00038001,
 	RPI_FIRMWARE_SET_CLOCK_RATE =                         0x00038002,
 	RPI_FIRMWARE_SET_VOLTAGE =                            0x00038003,
-- 
2.55.0