device: Provide de-init device function only if requested

This feature, fixing a specific corner case, is unilateraly growing
all struct device with a pointer that 99% of the time is not used.
Thus uselessly utilizing ROM.

Making the feature Kconfig controlled.

Signed-off-by: Tomasz Bursztyka <tobu@bang-olufsen.dk>

include/zephyr/device.h

@@ -144,6 +144,8 @@ typedef int16_t device_handle_t;
  * device from a devicetree node, use DEVICE_DT_DEINIT_DEFINE() or
  * DEVICE_DT_INST_DEINIT_DEFINE() instead.
  *
+ * Note: deinit_fn will only be used if CONFIG_DEVICE_DEINIT_SUPPORT is enabled.
+ *
  * @param dev_id A unique token which is used in the name of the global device
  * structure as a C identifier.
  * @param name A string name for the device, which will be stored in
@@ -214,6 +216,8 @@ typedef int16_t device_handle_t;
  * @kconfig{CONFIG_LLEXT_EXPORT_DEVICES} is enabled). Before using the
  * pointer, the referenced object should be checked using device_is_ready().
  *
+ * Note: deinit_fn will only be used if CONFIG_DEVICE_DEINIT_SUPPORT is enabled.
+ *
  * @param node_id The devicetree node identifier.
  * @param init_fn Pointer to the device's initialization function, which will be
  * run by the kernel during system initialization. Can be `NULL`.
@@ -494,8 +498,10 @@ typedef uint8_t device_flags_t;
 struct device_ops {
 	/** Initialization function */
 	int (*init)(const struct device *dev);
+#ifdef CONFIG_DEVICE_DEINIT_SUPPORT
 	/** De-initialization function */
 	int (*deinit)(const struct device *dev);
+#endif /* CONFIG_DEVICE_DEINIT_SUPPORT */
 };
 
 /**
@@ -881,6 +887,8 @@ __syscall int device_init(const struct device *dev);
  * acquired (e.g. pins, memory, clocks, DMA channels, etc.) and its status will
  * be left as in its reset state.
  *
+ * Note: this will be available if CONFIG_DEVICE_DEINIT_SUPPORT is enabled.
+ *
  * @warning It is the responsibility of the caller to ensure that the device is
  * ready to be de-initialized.
  *
@@ -888,7 +896,8 @@ __syscall int device_init(const struct device *dev);
  *
  * @retval 0 If successful
  * @retval -EPERM If device has not been initialized.
- * @retval -ENOTSUP If device does not support de-initialization.
+ * @retval -ENOTSUP If device does not support de-initialization, or if the
+ *         feature is not enabled (see CONFIG_DEVICE_DEINIT_SUPPORT)
  * @retval -errno For any other errors.
  */
 __syscall int device_deinit(const struct device *dev);
@@ -1132,6 +1141,19 @@ device_get_dt_nodelabels(const struct device *dev)
 	BUILD_ASSERT(sizeof(Z_STRINGIFY(name)) <= Z_DEVICE_MAX_NAME_LEN,       \
 			    Z_STRINGIFY(name) " too long")
 
+/**
+ * @brief Fill in the struct device_ops
+ *
+ * @param init_fn_ Initialization function
+ * @param deinit_fn_ De-initialization function
+ */
+#define Z_DEVICE_OPS(init_fn_, deinit_fn_)                                     \
+	{                                                                      \
+		.init = (init_fn_),                                            \
+		IF_ENABLED(CONFIG_DEVICE_DEINIT_SUPPORT,                       \
+			   (.deinit = (deinit_fn_),))                          \
+	}
+
 /**
  * @brief Initializer for @ref device.
  *
@@ -1156,7 +1178,7 @@ device_get_dt_nodelabels(const struct device *dev)
 		.api = (api_),								\
 		.state = (state_),							\
 		.data = (data_),							\
-		.ops = { .init = (init_fn_), .deinit = (deinit_fn_) },			\
+		.ops = Z_DEVICE_OPS(init_fn_, deinit_fn_),				\
 		.flags = (flags_),							\
 		IF_ENABLED(CONFIG_DEVICE_DEPS, (.deps = (deps_),)) /**/			\
 		IF_ENABLED(CONFIG_PM_DEVICE, Z_DEVICE_INIT_PM_BASE(pm_)) /**/		\

kernel/Kconfig.device

@@ -33,6 +33,16 @@ config DEVICE_DT_METADATA
 	  each device. This allows you to use device_get_by_dt_nodelabel(),
 	  device_get_dt_metadata(), etc.
 
+config DEVICE_DEINIT_SUPPORT
+	bool "Support device de-initialization"
+	default y
+	help
+	  In very specific case, it might be necessary to de-initialize
+	  a device at runtime. This is possible by providing a function
+	  to do so. Note, that this will grow every struct device by a
+	  function pointer. All device drivers that use the relevant
+	  macros and provide such function should select this option.
+
 endmenu
 
 menu "Initialization Priorities"

kernel/device.c

@@ -145,6 +145,7 @@ bool z_impl_device_is_ready(const struct device *dev)
 
 int z_impl_device_deinit(const struct device *dev)
 {
+#ifdef CONFIG_DEVICE_DEINIT_SUPPORT
 	int ret;
 
 	if (!dev->state->initialized) {
@@ -163,6 +164,10 @@ int z_impl_device_deinit(const struct device *dev)
 	dev->state->initialized = false;
 
 	return 0;
+#else
+	ARG_UNUSED(dev);
+	return -ENOTSUP;
+#endif /* CONFIG_DEVICE_DEINIT_SUPPORT */
 }
 
 #ifdef CONFIG_USERSPACE