soc: sophgo: cv1800: rtcsys: New driver (handling RTC only)

Add driver for Sophgo CV1800 series SoC RTC subsystem. The RTC module
comprises a 32kHz oscillator, Power-on-Reset (PoR) sub-module, HW state
machine to control chip power-on, power-off and reset. Furthermore, the
8051 subsystem is located within RTCSYS including associated SRAM block.

This patch only populates RTC sub-device.

Signed-off-by: Alexander Sverdlin <[email protected]>
Reviewed-by: Inochi Amaoto <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Inochi Amaoto <[email protected]>
Signed-off-by: Chen Wang <[email protected]>
Signed-off-by: Chen Wang <[email protected]>

Author: sverdlin

drivers/soc/sophgo/Kconfig

@@ -6,6 +6,19 @@
 if ARCH_SOPHGO || COMPILE_TEST
 menu "Sophgo SoC drivers"
 
+config SOPHGO_CV1800_RTCSYS
+	tristate "Sophgo CV1800 RTC MFD"
+	select MFD_CORE
+	help
+	  If you say yes here you get support the RTC MFD driver for Sophgo
+	  CV1800 series SoC. The RTC module comprises a 32kHz oscillator,
+	  Power-on-Reset (PoR) sub-module, HW state machine to control chip
+	  power-on, power-off and reset. Furthermore, the 8051 subsystem is
+	  located within RTCSYS including associated SRAM block.
+
+	  This driver can also be built as a module. If so, the module will be
+	  called cv1800-rtcsys.
+
 config SOPHGO_SG2044_TOPSYS
 	tristate "Sophgo SG2044 TOP syscon driver"
 	select MFD_CORE

drivers/soc/sophgo/Makefile

@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0
 
+obj-$(CONFIG_SOPHGO_CV1800_RTCSYS)	+= cv1800-rtcsys.o
 obj-$(CONFIG_SOPHGO_SG2044_TOPSYS)	+= sg2044-topsys.o

drivers/soc/sophgo/cv1800-rtcsys.c

@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for Sophgo CV1800 series SoC RTC subsystem
+ *
+ * The RTC module comprises a 32kHz oscillator, Power-on-Reset (PoR) sub-module,
+ * HW state machine to control chip power-on, power-off and reset. Furthermore,
+ * the 8051 subsystem is located within RTCSYS including associated SRAM block.
+ *
+ * Copyright (C) 2025 Alexander Sverdlin <[email protected]>
+ *
+ */
+
+#include <linux/mfd/core.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/property.h>
+
+static struct resource cv1800_rtcsys_irq_resources[] = {
+	DEFINE_RES_IRQ_NAMED(0, "alarm"),
+};
+
+static const struct mfd_cell cv1800_rtcsys_subdev[] = {
+	{
+		.name = "cv1800b-rtc",
+		.num_resources = 1,
+		.resources = &cv1800_rtcsys_irq_resources[0],
+	},
+};
+
+static int cv1800_rtcsys_probe(struct platform_device *pdev)
+{
+	int irq;
+
+	irq = platform_get_irq_byname(pdev, "alarm");
+	if (irq < 0)
+		return irq;
+	cv1800_rtcsys_irq_resources[0].start = irq;
+	cv1800_rtcsys_irq_resources[0].end = irq;
+
+	return devm_mfd_add_devices(&pdev->dev, PLATFORM_DEVID_AUTO,
+				    cv1800_rtcsys_subdev,
+				    ARRAY_SIZE(cv1800_rtcsys_subdev),
+				    NULL, 0, NULL);
+}
+
+static const struct of_device_id cv1800_rtcsys_of_match[] = {
+	{ .compatible = "sophgo,cv1800b-rtc" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, cv1800_rtcsys_of_match);
+
+static struct platform_driver cv1800_rtcsys_mfd = {
+	.probe	= cv1800_rtcsys_probe,
+	.driver	= {
+		.name		= "cv1800_rtcsys",
+		.of_match_table	= cv1800_rtcsys_of_match,
+	},
+};
+module_platform_driver(cv1800_rtcsys_mfd);
+
+MODULE_AUTHOR("Alexander Sverdlin <[email protected]>");
+MODULE_DESCRIPTION("Sophgo CV1800 series SoC RTC subsystem driver");
+MODULE_LICENSE("GPL");