drivers: bbram: Enables bbram driver for motorola, mc146818

Enables bbram driver for motorola, mc146818 under its MFD to access the RAM of the RTC.

Signed-off-by: Anisetti Avinash Krishna <anisetti.avinash.krishna@intel.com>

Author: akanisetti

drivers/bbram/CMakeLists.txt

@@ -18,3 +18,4 @@ zephyr_library_sources_ifdef(CONFIG_BBRAM_MICROCHIP_MCP7940N_EMUL bbram_microchi
 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)
+zephyr_library_sources_ifdef(CONFIG_BBRAM_MOTOROLA_MC146818 bbram_mc146818.c)

drivers/bbram/Kconfig

@@ -44,4 +44,6 @@ source "drivers/bbram/Kconfig.stm32"
 
 source "drivers/bbram/Kconfig.rts5912"
 
+source "drivers/bbram/Kconfig.mc146818"
+
 endif # BBRAM

drivers/bbram/Kconfig.mc146818

@@ -0,0 +1,12 @@
+# Intel SoC BBRAM configuration options
+
+# Copyright (c) 2025 Intel Corporation
+# SPDX-License-Identifier: Apache-2.0
+
+config BBRAM_MOTOROLA_MC146818
+	bool "BBRAM driver for x86 CMOS/RTC clock's bbram"
+	default y if !COUNTER
+	select MFD
+	depends on DT_HAS_MOTOROLA_MC146818_BBRAM_ENABLED
+	help
+	  Enable driver for Motorola mc146818 BBRAM.

drivers/bbram/bbram_mc146818.c

@@ -0,0 +1,155 @@
+/*
+ * Copyright (c) 2025 Intel Corporation.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * Read and Write access to offset ranges 0x2A(42)-0x31(49) and 0xAA(170)-0xB1(177)
+ * are lockable through BIOS setting. To access the memory in those offsets,
+ * disable the Lock in BIOS through following steps.
+ * Intel Advanced Menu -> PCH-IO Configuration -> Security Configuration ->
+ * RTC Memory Lock -> Disable
+ */
+
+#define DT_DRV_COMPAT motorola_mc146818_bbram
+
+#include <zephyr/device.h>
+#include <zephyr/kernel.h>
+#include <zephyr/init.h>
+#include <zephyr/sys/util.h>
+#include <zephyr/devicetree.h>
+#include <zephyr/drivers/bbram.h>
+#include <zephyr/sys/sys_io.h>
+#include <zephyr/spinlock.h>
+#include <zephyr/drivers/mfd/mc146818.h>
+
+#define MIN_SIZE	1 /* Minimum size to write */
+#define MIN_OFFSET	0x0E /* Starting offset of memory */
+#define MAX_STD		0x7F /* Last offset of Standard memory bank */
+#define RTC_CENT	0x32 /* Offset for RTC Century Byte */
+
+struct bbram_mc146818_config {
+	const struct device *mfd;
+	size_t mem_size;
+};
+
+struct bbram_mc146818_data {
+	struct k_spinlock lock;
+};
+
+static int bbram_mc146818_read(const struct device *dev, size_t offset,
+			    size_t size, uint8_t *data)
+{
+	const struct bbram_mc146818_config *config = dev->config;
+	struct bbram_mc146818_data *dev_data = dev->data;
+
+	if (size < MIN_SIZE || offset + size > config->mem_size
+	    || data == NULL) {
+		return -EFAULT;
+	}
+
+	offset += MIN_OFFSET;
+
+	k_spinlock_key_t key = k_spin_lock(&dev_data->lock);
+
+	for (size_t i = 0; i < size; i++) {
+		if (offset < MAX_STD) {
+			if (offset >= RTC_CENT) {
+
+			/* RTC_CENT byte is used to store Century data for the
+			 * RTC time and date, so skipping read/write operation
+			 * to this byte.
+			 */
+
+				*(data + i) = mfd_mc146818_std_read(config->mfd, offset+1);
+			} else {
+				*(data + i) = mfd_mc146818_std_read(config->mfd, offset);
+			}
+		} else {
+			*(data + i) = mfd_mc146818_ext_read(config->mfd, offset+1);
+		}
+		offset++;
+	}
+
+	k_spin_unlock(&dev_data->lock, key);
+	return 0;
+}
+
+static int bbram_mc146818_write(const struct device *dev, size_t offset,
+			     size_t size, const uint8_t *data)
+{
+	const struct bbram_mc146818_config *config = dev->config;
+	struct bbram_mc146818_data *dev_data = dev->data;
+
+	if (size < MIN_SIZE || offset + size > config->mem_size
+	    || data == NULL) {
+		return -EFAULT;
+	}
+
+	offset += MIN_OFFSET;
+
+	k_spinlock_key_t key = k_spin_lock(&dev_data->lock);
+
+	for (size_t i = 0; i < size; i++) {
+		if (offset < MAX_STD) {
+			if (offset >= RTC_CENT) {
+
+			/* RTC_CENT byte is used to store Century data for the
+			 * RTC time and date, so skipping read/write operation
+			 * to this byte.
+			 */
+
+				mfd_mc146818_std_write(config->mfd, offset+1, *(data + i));
+			} else {
+				mfd_mc146818_std_write(config->mfd, offset, *(data + i));
+			}
+		} else {
+			mfd_mc146818_ext_write(config->mfd, offset+1, *(data + i));
+		}
+		offset++;
+	}
+
+	k_spin_unlock(&dev_data->lock, key);
+	return 0;
+}
+
+static int bbram_mc146818_get_size(const struct device *dev, size_t *size)
+{
+	const struct bbram_mc146818_config *config = dev->config;
+
+	*size = config->mem_size;
+
+	return 0;
+}
+
+static const struct bbram_driver_api bbram_mc146818_api = {
+	.read = bbram_mc146818_read,
+	.write = bbram_mc146818_write,
+	.get_size = bbram_mc146818_get_size,
+};
+
+static int bbram_mc146818_init(const struct device *dev)
+{
+	const struct bbram_mc146818_config *config = dev->config;
+
+	if (!device_is_ready(config->mfd)) {
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+#define BBRAM_MC146818_DEV_CFG(n)					\
+	static const struct bbram_mc146818_config bbram_config_##n = {	\
+		.mfd = DEVICE_DT_GET(DT_INST_PARENT(n)),		\
+		.mem_size = DT_INST_PROP(n, size),			\
+	};								\
+	static struct bbram_mc146818_data bbram_data_##n;		\
+	DEVICE_DT_INST_DEFINE(n, &bbram_mc146818_init, NULL,		\
+				&bbram_data_##n, &bbram_config_##n,	\
+				POST_KERNEL,				\
+				CONFIG_KERNEL_INIT_PRIORITY_DEVICE,	\
+				&bbram_mc146818_api);			\
+
+DT_INST_FOREACH_STATUS_OKAY(BBRAM_MC146818_DEV_CFG)

dts/bindings/memory-controllers/motorola,mc146818-bbram.yaml

@@ -0,0 +1,15 @@
+# Copyright (c) 2025, Intel Corporation
+#
+# SPDX-License-Identifier: Apache-2.0
+
+description: Motorola MC146818 compatible Real Timer Clock Battery Backed RAM
+
+compatible: "motorola,mc146818-bbram"
+
+include: base.yaml
+
+properties:
+  size:
+    type: int
+    required: true
+    description: Memory capacity in bytes.