emul: Add support for backend APIs

The emulator structure currently initializes a bus-level API that is
used to communicated register accesses to the emulator from the parent
bus.

Add support for declaring a backend API for emulators. This provides
tests a common way to interact with emulators of the same device type.

Signed-off-by: Keith Short <[email protected]>

Author: keith-zephyr

include/zephyr/drivers/emul.h

@@ -81,6 +81,8 @@ struct emul {
 		struct espi_emul *espi;
 		struct spi_emul *spi;
 	} bus;
+	/** Address of the API structure exposed by the emulator instance */
+	const void *backend_api;
 };
 
 /**
@@ -120,8 +122,9 @@ extern const struct emul __emul_list_end[];
  * @param data_ptr emulator-specific data
  * @param cfg_ptr emulator-specific configuration data
  * @param bus_api emulator-specific bus api
+ * @param _backend_api emulator-specific backend api
  */
-#define EMUL_DT_DEFINE(node_id, init_fn, data_ptr, cfg_ptr, bus_api)                               \
+#define EMUL_DT_DEFINE(node_id, init_fn, data_ptr, cfg_ptr, bus_api, _backend_api)                 \
 	static struct Z_EMUL_BUS(node_id, i2c_emul, espi_emul, spi_emul)                           \
 		Z_EMUL_REG_BUS_IDENTIFIER(node_id) = {                                             \
 			.api = bus_api,                                                            \
@@ -137,6 +140,7 @@ extern const struct emul __emul_list_end[];
 				       EMUL_BUS_TYPE_SPI),                                         \
 		.bus = {.Z_EMUL_BUS(node_id, i2c, espi, spi) =                                     \
 				&(Z_EMUL_REG_BUS_IDENTIFIER(node_id))},                            \
+		.backend_api = (_backend_api),                                                     \
 	};
 
 /**

subsys/emul/emul_bmi160.c

@@ -318,9 +318,9 @@ static int emul_bosch_bmi160_init(const struct emul *target, const struct device
 	static uint8_t bmi160_emul_reg_##n[BMI160_REG_COUNT];                                      \
 	static struct bmi160_emul_data bmi160_emul_data_##n;
 
-#define BMI160_EMUL_DEFINE(n, api)                                                                 \
+#define BMI160_EMUL_DEFINE(n, bus_api)                                                             \
 	EMUL_DT_INST_DEFINE(n, emul_bosch_bmi160_init, &bmi160_emul_data_##n,                      \
-			    &bmi160_emul_cfg_##n, &api)
+			    &bmi160_emul_cfg_##n, &bus_api, NULL)
 
 /* Instantiation macros used when a device is on a SPI bus */
 #define BMI160_EMUL_SPI(n)                                                                         \

subsys/emul/espi/emul_espi_host.c

@@ -263,6 +263,6 @@ static int emul_host_init(const struct emul *emul, const struct device *bus)
 		.chipsel = DT_INST_REG_ADDR(n),                                                    \
 	};                                                                                         \
 	EMUL_DT_INST_DEFINE(n, emul_host_init, &espi_host_emul_data_##n, &espi_host_emul_cfg_##n,  \
-			    &ap_emul_api)
+			    &ap_emul_api, NULL)
 
 DT_INST_FOREACH_STATUS_OKAY(HOST_EMUL)

subsys/emul/i2c/emul_atmel_at24.c

@@ -162,6 +162,6 @@ static int emul_atmel_at24_init(const struct emul *target, const struct device *
 		.addr_width = 8,                                                                   \
 	};                                                                                         \
 	EMUL_DT_INST_DEFINE(n, emul_atmel_at24_init, &at24_emul_data_##n, &at24_emul_cfg_##n,      \
-			    &bus_api)
+			    &bus_api, NULL)
 
 DT_INST_FOREACH_STATUS_OKAY(EEPROM_AT24_EMUL)

subsys/emul/i2c/emul_sbs_gauge.c

@@ -174,6 +174,6 @@ static int emul_sbs_sbs_gauge_init(const struct emul *target, const struct devic
 		.addr = DT_INST_REG_ADDR(n),                                                       \
 	};                                                                                         \
 	EMUL_DT_INST_DEFINE(n, emul_sbs_sbs_gauge_init, &sbs_gauge_emul_data_##n,                  \
-			    &sbs_gauge_emul_cfg_##n, &sbs_gauge_emul_api_i2c)
+			    &sbs_gauge_emul_cfg_##n, &sbs_gauge_emul_api_i2c, NULL)
 
 DT_INST_FOREACH_STATUS_OKAY(SBS_GAUGE_EMUL)