driver: bbram: add bbram driver for rts5912

Add bbram driver for Realtek rts5912.

Signed-off-by: Elmo Lan <elmo_lan@realtek.com>

drivers/bbram/CMakeLists.txt

@@ -17,3 +17,4 @@ zephyr_library_sources_ifdef(CONFIG_BBRAM_MICROCHIP_MCP7940N bbram_microchip_mcp
 zephyr_library_sources_ifdef(CONFIG_BBRAM_MICROCHIP_MCP7940N_EMUL bbram_microchip_mcp7940n_emul.c)
 zephyr_library_sources_ifdef(CONFIG_BBRAM_XEC bbram_xec.c)
 zephyr_library_sources_ifdef(CONFIG_BBRAM_STM32 bbram_stm32.c)
+zephyr_library_sources_ifdef(CONFIG_BBRAM_RTS5912 bbram_rts5912.c)

drivers/bbram/Kconfig

@@ -42,4 +42,6 @@ source "drivers/bbram/Kconfig.xec"
 
 source "drivers/bbram/Kconfig.stm32"
 
+source "drivers/bbram/Kconfig.rts5912"
+
 endif # BBRAM

drivers/bbram/Kconfig.rts5912

@@ -0,0 +1,9 @@
+# Copyright (c) 2025, Realtek, SIBG-SD7
+# SPDX-License-Identifier: Apache-2.0
+
+config BBRAM_RTS5912
+	bool "Realtek RTS5912 Battery-backed RAM drivers"
+	default y
+	depends on DT_HAS_REALTEK_RTS5912_BBRAM_ENABLED
+	help
+	  This option enables the BBRAM driver for Realtek RTS5912 of processors.

drivers/bbram/bbram_rts5912.c

@@ -0,0 +1,99 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Copyright (c) 2025 Realtek Semiconductor Corporation, SIBG-SD7
+ * Author: Elmo Lan <elmo_lan@realtek.com>
+ */
+
+#define DT_DRV_COMPAT realtek_rts5912_bbram
+
+#include <zephyr/drivers/bbram.h>
+#include <errno.h>
+#include <zephyr/sys/util.h>
+
+#include <zephyr/logging/log.h>
+LOG_MODULE_REGISTER(rts5912_bbram, CONFIG_BBRAM_LOG_LEVEL);
+
+struct bbram_rts5912_config {
+	uintptr_t base;
+	int size;
+};
+
+static int bbram_rts5912_get_size(const struct device *dev, size_t *size)
+{
+	const struct bbram_rts5912_config *config = dev->config;
+
+	*size = config->size;
+	LOG_INF("size: 0x%08x", *size);
+	return 0;
+}
+
+static int bbram_rts5912_read(const struct device *dev, size_t offset, size_t size, uint8_t *data)
+{
+	const struct bbram_rts5912_config *config = dev->config;
+
+	uint32_t word;
+	size_t start_offset, bytes_to_read;
+
+	if (size < 1 || offset + size > config->size) {
+		LOG_ERR("Invalid params");
+		return -EFAULT;
+	}
+
+	/* The bbram in RTS5912 only accepts word-access.
+	 * Read it as a word, then split it into bytes.
+	 */
+	for (int i = 0; i < size;) {
+		word = *(uint32_t *)(config->base + ROUND_DOWN((offset + i), 4));
+		start_offset = (offset + i) % 4;
+		bytes_to_read = MIN(4 - start_offset, size - i);
+		memcpy(&data[i], ((uint8_t *)&word) + start_offset, bytes_to_read);
+		i += bytes_to_read;
+	}
+
+	return 0;
+}
+
+static int bbram_rts5912_write(const struct device *dev, size_t offset, size_t size,
+			       const uint8_t *data)
+{
+	const struct bbram_rts5912_config *config = dev->config;
+
+	uint32_t word;
+	size_t start_offset, bytes_to_write;
+
+	if (size < 1 || offset + size > config->size) {
+		LOG_ERR("Invalid params");
+		return -EFAULT;
+	}
+
+	/* The BBRAM in RTS5912 only accepts word-access. Read it as a word,
+	 * then modify the byte field, and finally write it back as a word
+	 */
+	for (int i = 0; i < size;) {
+		word = *(uint32_t *)(config->base + ROUND_DOWN((offset + i), 4));
+		start_offset = (offset + i) % 4;
+		bytes_to_write = MIN(4 - start_offset, size - i);
+		memcpy(((uint8_t *)&word) + start_offset, &data[i], bytes_to_write);
+		*(uint32_t *)(config->base + ROUND_DOWN((offset + i), 4)) = word;
+		i += bytes_to_write;
+	}
+
+	return 0;
+}
+
+static DEVICE_API(bbram, bbram_rts5912_driver_api) = {
+	.get_size = bbram_rts5912_get_size,
+	.read = bbram_rts5912_read,
+	.write = bbram_rts5912_write,
+};
+
+#define BBRAM_INIT(inst)                                                                           \
+	static const struct bbram_rts5912_config bbram_cfg_##inst = {                              \
+		.base = DT_INST_REG_ADDR(inst),                                                    \
+		.size = DT_INST_REG_SIZE(inst),                                                    \
+	};                                                                                         \
+	DEVICE_DT_INST_DEFINE(inst, NULL, NULL, NULL, &bbram_cfg_##inst, PRE_KERNEL_1,             \
+			      CONFIG_BBRAM_INIT_PRIORITY, &bbram_rts5912_driver_api);
+
+DT_INST_FOREACH_STATUS_OKAY(BBRAM_INIT);

dts/arm/realtek/ec/rts5912.dtsi

@@ -65,6 +65,12 @@
 		interrupt-parent = <&nvic>;
 		ranges;
 
+		bbram: bb-ram@40005000 {
+			compatible = "realtek,rts5912-bbram";
+			reg = <0x40005000 0x100>;
+			status = "okay";
+		};
+
 		sccon: clock-controller@40020000 {
 			compatible = "realtek,rts5912-sccon";
 			reg = <0x40020000 0xf0>;

dts/bindings/memory-controllers/realtek,rts5912-bbram.yaml

@@ -0,0 +1,12 @@
+# Copyright (c) 2025, Realtek, SIBG-SD7
+# SPDX-License-Identifier: Apache-2.0
+
+description: Realtek, RTS5912 Battery Backed RAM node
+
+compatible: "realtek,rts5912-bbram"
+
+include: base.yaml
+
+properties:
+  reg:
+    required: true