bbram: mcp7940c: Add emulator

Add an emulator for the mcp7940c BBRAM that supports reading and writing.

Signed-off-by: Yuval Peress <peress@google.com>

drivers/bbram/CMakeLists.txt

@@ -12,5 +12,6 @@ zephyr_library_sources_ifdef(CONFIG_BBRAM_IT8XXX2_EMUL bbram_it8xxx2_emul.c)
 zephyr_library_include_directories_ifdef(CONFIG_BBRAM_IT8XXX2 .)
 zephyr_library_sources_ifdef(CONFIG_BBRAM_EMUL bbram_emul.c)
 zephyr_library_sources_ifdef(CONFIG_BBRAM_MICROCHIP_MCP7940N bbram_microchip_mcp7940n.c)
+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)

drivers/bbram/Kconfig.microchip

@@ -8,3 +8,12 @@ config BBRAM_MICROCHIP_MCP7940N
 	select I2C
 	help
 	  Enable driver for Microchip MCP7940N SRAM based battery-backed RAM.
+
+config BBRAM_MICROCHIP_MCP7940N_EMUL
+	bool "Emulator for the Microchip MCP7940N SRAM BBRAM driver"
+	default y
+	depends on BBRAM_MICROCHIP_MCP7940N
+	depends on EMUL
+	help
+	  Enable the emulator for the Microchip MCP7940N SRAM based
+	  battery-backed RAM.

drivers/bbram/bbram_microchip_mcp7940n.c

@@ -153,7 +153,7 @@ static int microchip_mcp7940n_bbram_read(const struct device *dev, size_t offset
 	size_t i = 0;
 	int32_t rc = 0;
 
-	if ((offset + size) > MICROCHIP_MCP7940N_SRAM_SIZE) {
+	if (size == 0 || (offset + size) > MICROCHIP_MCP7940N_SRAM_SIZE) {
 		return -EINVAL;
 	}
 
@@ -186,7 +186,7 @@ static int microchip_mcp7940n_bbram_write(const struct device *dev, size_t offse
 	size_t i = 0;
 	int32_t rc = 0;
 
-	if ((offset + size) > MICROCHIP_MCP7940N_SRAM_SIZE) {
+	if (size == 0 || (offset + size) > MICROCHIP_MCP7940N_SRAM_SIZE) {
 		return -EINVAL;
 	}
 

drivers/bbram/bbram_microchip_mcp7940n_emul.c

@@ -0,0 +1,150 @@
+/*
+ * Copyright 2024 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#define DT_DRV_COMPAT microchip_mcp7940n
+
+#include <zephyr/device.h>
+#include <zephyr/drivers/emul.h>
+#include <zephyr/drivers/emul_bbram.h>
+#include <zephyr/drivers/i2c.h>
+#include <zephyr/drivers/i2c_emul.h>
+#include <zephyr/logging/log.h>
+
+LOG_MODULE_DECLARE(bbram_microchip_mcp7940n, CONFIG_BBRAM_LOG_LEVEL);
+
+#define MICROCHIP_MCP7940N_SRAM_OFFSET               0x20
+#define MICROCHIP_MCP7940N_SRAM_SIZE                 64
+#define MICROCHIP_MCP7940N_RTCWKDAY_REGISTER_ADDRESS 0x03
+#define MICROCHIP_MCP7940N_RTCWKDAY_VBATEN_BIT       BIT(3)
+#define MICROCHIP_MCP7940N_RTCWKDAY_PWRFAIL_BIT      BIT(4)
+
+struct mcp7940n_emul_cfg {
+};
+
+struct mcp7940n_emul_data {
+	uint8_t rtcwkday;
+	uint8_t data[MICROCHIP_MCP7940N_SRAM_SIZE];
+};
+
+static int mcp7940n_emul_init(const struct emul *target, const struct device *parent)
+{
+	ARG_UNUSED(target);
+	ARG_UNUSED(parent);
+	return 0;
+}
+
+static int mcp7940n_emul_transfer_i2c(const struct emul *target, struct i2c_msg *msgs, int num_msgs,
+				      int addr)
+{
+	struct mcp7940n_emul_data *data = target->data;
+
+	i2c_dump_msgs_rw(target->dev, msgs, num_msgs, addr, false);
+
+	if (num_msgs < 1) {
+		LOG_ERR("Invalid number of messages: %d", num_msgs);
+		return -EIO;
+	}
+	if (FIELD_GET(I2C_MSG_READ, msgs->flags)) {
+		LOG_ERR("Unexpected read");
+		return -EIO;
+	}
+	if (msgs->len < 1) {
+		LOG_ERR("Unexpected msg0 length %d", msgs->len);
+		return -EIO;
+	}
+
+	uint8_t regn = msgs->buf[0];
+	bool is_read = FIELD_GET(I2C_MSG_READ, msgs->flags) == 1;
+	bool is_stop = FIELD_GET(I2C_MSG_STOP, msgs->flags) == 1;
+
+	if (!is_stop && !is_read) {
+		/* First message was a write with the register number, check next message */
+		msgs++;
+		is_read = FIELD_GET(I2C_MSG_READ, msgs->flags) == 1;
+		is_stop = FIELD_GET(I2C_MSG_STOP, msgs->flags) == 1;
+	}
+
+	if (is_read) {
+		/* Read data */
+		if (regn == MICROCHIP_MCP7940N_RTCWKDAY_REGISTER_ADDRESS) {
+			msgs->buf[0] = data->rtcwkday;
+			return 0;
+		}
+		if (regn >= MICROCHIP_MCP7940N_SRAM_OFFSET &&
+		    regn + msgs->len <=
+			    MICROCHIP_MCP7940N_SRAM_OFFSET + MICROCHIP_MCP7940N_SRAM_SIZE) {
+			for (int i = 0; i < msgs->len; ++i) {
+				msgs->buf[i] =
+					data->data[regn + i - MICROCHIP_MCP7940N_SRAM_OFFSET];
+			}
+			return 0;
+		}
+	} else {
+		/* Write data */
+		if (regn == MICROCHIP_MCP7940N_RTCWKDAY_REGISTER_ADDRESS) {
+			data->rtcwkday = msgs->buf[1];
+			return 0;
+		}
+		if (regn >= MICROCHIP_MCP7940N_SRAM_OFFSET &&
+		    regn + msgs->len - 1 <=
+			    MICROCHIP_MCP7940N_SRAM_OFFSET + MICROCHIP_MCP7940N_SRAM_SIZE) {
+			for (int i = 0; i < msgs->len; ++i) {
+				data->data[regn + i - MICROCHIP_MCP7940N_SRAM_OFFSET] =
+					msgs->buf[1 + i];
+			}
+			return 0;
+		}
+	}
+
+	return -EIO;
+}
+
+static const struct i2c_emul_api mcp7940n_emul_api_i2c = {
+	.transfer = mcp7940n_emul_transfer_i2c,
+};
+
+static int mcp7940n_emul_backend_set_data(const struct emul *target, size_t offset, size_t count,
+					  const uint8_t *buffer)
+{
+	struct mcp7940n_emul_data *data = target->data;
+
+	if (offset + count > MICROCHIP_MCP7940N_SRAM_SIZE) {
+		return -ERANGE;
+	}
+
+	for (size_t i = 0; i < count; ++i) {
+		data->data[offset + i] = buffer[i];
+	}
+	return 0;
+}
+
+static int mcp7940n_emul_backend_get_data(const struct emul *target, size_t offset, size_t count,
+					  uint8_t *buffer)
+{
+	struct mcp7940n_emul_data *data = target->data;
+
+	if (offset + count > MICROCHIP_MCP7940N_SRAM_SIZE) {
+		return -ERANGE;
+	}
+
+	for (size_t i = 0; i < count; ++i) {
+		buffer[i] = data->data[offset + i];
+	}
+	return 0;
+}
+
+static const struct emul_bbram_backend_api mcp7940n_emul_backend_api = {
+	.set_data = mcp7940n_emul_backend_set_data,
+	.get_data = mcp7940n_emul_backend_get_data,
+};
+
+#define MCP7940N_EMUL(inst)                                                                        \
+	static const struct mcp7940n_emul_cfg mcp7940n_emul_cfg_##inst;                            \
+	static struct mcp7940n_emul_data mcp7940n_emul_data_##inst;                                \
+	EMUL_DT_INST_DEFINE(inst, mcp7940n_emul_init, &mcp7940n_emul_data_##inst,                  \
+			    &mcp7940n_emul_cfg_##inst, &mcp7940n_emul_api_i2c,                     \
+			    &mcp7940n_emul_backend_api)
+
+DT_INST_FOREACH_STATUS_OKAY(MCP7940N_EMUL)