rtio: Add default i2c submit handler

Use the RTIO work queue to fake the i2c submit calls for drivers which
haven't yet implemented the API. Applications can change the size of
the work queue pool depending on how much traffic they have on the buses.

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

Author: yperess

doc/services/rtio/index.rst

@@ -212,6 +212,20 @@ There is a small cost to each RTIO context and iodev. This cost could be weighed
 against using a thread for each concurrent I/O operation or custom queues and
 threads per peripheral. RTIO is much lower cost than that.
 
+Supported Buses
+***************
+
+To check if your bus supports RTIO natively, you can check the driver API implementation, if the
+driver implements the ``iodev_submit`` function of the bus API, then RTIO is supported. If the
+driver doesn't support the RTIO APIs, it will set the submit function to
+``i2c_iodev_submit_fallback``.
+
+I2C buses have a default implementation which allows apps to leverage the RTIO work queue while
+vendors implement the submit function. With this queue, any I2C bus driver that does not implement
+the ``iodev_submit`` function will defer to a work item which will perform a blocking I2C
+transaction. To change the pool size, set a different value to
+:kconfig:option`CONFIG_RTIO_WORKQ_POOL_ITEMS`.
+
 API Reference
 *************
 

drivers/i2c/CMakeLists.txt

@@ -6,7 +6,10 @@ zephyr_library()
 
 zephyr_library_sources(i2c_common.c)
 
-zephyr_library_sources_ifdef(CONFIG_I2C_RTIO i2c_rtio.c)
+zephyr_library_sources_ifdef(CONFIG_I2C_RTIO
+	i2c_rtio.c
+	i2c_rtio_default.c
+)
 zephyr_library_sources_ifdef(CONFIG_I2C_SHELL		i2c_shell.c)
 zephyr_library_sources_ifdef(CONFIG_I2C_BITBANG		i2c_bitbang.c)
 zephyr_library_sources_ifdef(CONFIG_I2C_TELINK_B91		i2c_b91.c)

drivers/i2c/Kconfig

@@ -54,16 +54,11 @@ config I2C_CALLBACK
 	help
 	  API and implementations of i2c_transfer_cb.
 
-config HAS_I2C_RTIO
-	bool
-	help
-	  This option must be selected by I2C controller drivers that optionally implement the RTIO
-	  interface.
-
 config I2C_RTIO
 	bool "I2C RTIO API"
-	depends on HAS_I2C_RTIO
+	select EXPERIMENTAL
 	select RTIO
+	select RTIO_WORKQ
 	help
 	  API and implementations of I2C for RTIO
 
@@ -177,7 +172,6 @@ config I2C_MCUX_LPI2C
 	default y
 	depends on DT_HAS_NXP_IMX_LPI2C_ENABLED
 	depends on CLOCK_CONTROL
-	select HAS_I2C_RTIO
 	select PINCTRL
 	help
 	  Enable the mcux LPI2C driver.

drivers/i2c/Kconfig.nrfx

@@ -17,7 +17,6 @@ if I2C_NRFX
 config I2C_NRFX_TWI
 	def_bool y
 	depends on DT_HAS_NORDIC_NRF_TWI_ENABLED
-	select HAS_I2C_RTIO
 	select NRFX_TWI0 if HAS_HW_NRF_TWI0
 	select NRFX_TWI1 if HAS_HW_NRF_TWI1
 

drivers/i2c/Kconfig.sam_twihs

@@ -7,6 +7,5 @@ config I2C_SAM_TWIHS
 	bool "Atmel SAM (TWIHS) I2C driver"
 	default y
 	depends on DT_HAS_ATMEL_SAM_I2C_TWIHS_ENABLED
-	select HAS_I2C_RTIO
 	help
 	  Enable Atmel SAM MCU Family (TWIHS) I2C bus driver.

drivers/i2c/gpio_i2c_switch.c

@@ -67,6 +67,9 @@ static int gpio_i2c_switch_transfer(const struct device *dev, struct i2c_msg *ms
 static const struct i2c_driver_api gpio_i2c_switch_api_funcs = {
 	.configure = gpio_i2c_switch_configure,
 	.transfer = gpio_i2c_switch_transfer,
+#ifdef CONFIG_I2C_RTIO
+	.iodev_submit = i2c_iodev_submit_fallback,
+#endif
 };
 
 static int gpio_i2c_switch_init(const struct device *dev)

drivers/i2c/i2c_ambiq.c

@@ -275,6 +275,9 @@ static int i2c_ambiq_init(const struct device *dev)
 static const struct i2c_driver_api i2c_ambiq_driver_api = {
 	.configure = i2c_ambiq_configure,
 	.transfer = i2c_ambiq_transfer,
+#ifdef CONFIG_I2C_RTIO
+	.iodev_submit = i2c_iodev_submit_fallback,
+#endif
 };
 
 #ifdef CONFIG_PM_DEVICE

drivers/i2c/i2c_andes_atciic100.c

@@ -733,13 +733,14 @@ static void i2c_atciic100_irq_handler(void *arg)
 }
 
 static const struct i2c_driver_api i2c_atciic100_driver = {
-	.configure		= (i2c_api_configure_t)i2c_atciic100_configure,
-	.transfer		= (i2c_api_full_io_t)i2c_atciic100_transfer,
+	.configure = (i2c_api_configure_t)i2c_atciic100_configure,
+	.transfer = (i2c_api_full_io_t)i2c_atciic100_transfer,
 #if defined(CONFIG_I2C_TARGET)
-	.target_register	=
-		(i2c_api_target_register_t)i2c_atciic100_target_register,
-	.target_unregister	=
-		(i2c_api_target_unregister_t)i2c_atciic100_target_unregister
+	.target_register = (i2c_api_target_register_t)i2c_atciic100_target_register,
+	.target_unregister = (i2c_api_target_unregister_t)i2c_atciic100_target_unregister,
+#endif
+#ifdef CONFIG_I2C_RTIO
+	.iodev_submit = i2c_iodev_submit_fallback,
 #endif
 };
 

drivers/i2c/i2c_b91.c

@@ -150,6 +150,9 @@ static int i2c_b91_init(const struct device *dev)
 static const struct i2c_driver_api i2c_b91_api = {
 	.configure = i2c_b91_configure,
 	.transfer = i2c_b91_transfer,
+#ifdef CONFIG_I2C_RTIO
+	.iodev_submit = i2c_iodev_submit_fallback,
+#endif
 };
 
 BUILD_ASSERT(DT_NUM_INST_STATUS_OKAY(DT_DRV_COMPAT) <= 1,

drivers/i2c/i2c_bcm_iproc.c

@@ -923,6 +923,9 @@ static const struct i2c_driver_api iproc_i2c_driver_api = {
 	.target_register = iproc_i2c_target_register,
 	.target_unregister = iproc_i2c_target_unregister,
 #endif
+#ifdef CONFIG_I2C_RTIO
+	.iodev_submit = i2c_iodev_submit_fallback,
+#endif
 };
 
 #define IPROC_I2C_DEVICE_INIT(n)                                                                   \