pm: device: remove CONFIG_PM_MAX_DEVICES

When a device is defined a new pointer to a device will be created in
the "z_pm_device_slots" region, effectively creating a device array with
the same size as the number of system devices. This array is then used
by the device PM subsystem to keep track of suspended devices during
power transitions.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

include/device.h

@@ -692,11 +692,27 @@ int device_busy_check(const struct device *chk_dev);
 #define Z_DEVICE_EXTRA_HANDLES(...)				\
 	FOR_EACH_NONEMPTY_TERM(IDENTITY, (,), __VA_ARGS__)
 
+/* If device power management is enabled, this macro defines a pointer to a
+ * device in the z_pm_device_slots region. When invoked for each device, this
+ * will effectively result in a device pointer array with the same size of the
+ * actual devices list. This is used internally by the device PM subsystem to
+ * keep track of suspended devices during system power transitions.
+ */
+#if CONFIG_PM_DEVICE
+#define Z_DEVICE_DEFINE_PM_SLOT(dev_name)				\
+	static const Z_DECL_ALIGN(struct device *)			\
+	_CONCAT(__pm_device_slot_, DEVICE_NAME_GET(dev_name)) __used	\
+	__attribute__((__section__(".z_pm_device_slots")));
+#else
+#define Z_DEVICE_DEFINE_PM_SLOT(dev_name)
+#endif
+
 /* Construct objects that are referenced from struct device.  These
  * include power management and dependency handles.
  */
 #define Z_DEVICE_DEFINE_PRE(node_id, dev_name, ...)			\
-	Z_DEVICE_DEFINE_HANDLES(node_id, dev_name, __VA_ARGS__)
+	Z_DEVICE_DEFINE_HANDLES(node_id, dev_name, __VA_ARGS__)		\
+	Z_DEVICE_DEFINE_PM_SLOT(dev_name)
 
 
 /* Initial build provides a record that associates the device object

include/linker/common-ram.ld

@@ -37,6 +37,15 @@
 		__device_end = .;
 	} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
 
+#if CONFIG_PM_DEVICE
+	SECTION_DATA_PROLOGUE(pm_device_slots, (NOLOAD),)
+	{
+		__pm_device_slots_start = .;
+		KEEP(*(".z_pm_device_slots"));
+		__pm_device_slots_end = .;
+	} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
+#endif
+
 	SECTION_DATA_PROLOGUE(initshell,,)
 	{
 		/* link in shell initialization objects for all modules that

subsys/pm/Kconfig

@@ -60,11 +60,6 @@ config DEVICE_POWER_MANAGEMENT
 	help
 	  This option is deprecated, please use CONFIG_PM_DEVICE instead.
 
-config PM_MAX_DEVICES
-	int "Max number of devices support power management"
-	depends on PM_DEVICE
-	default 15
-
 config PM_DEVICE_RUNTIME
 	bool "Runtime Device Power Management"
 	depends on PM_DEVICE

subsys/pm/device.c

@@ -18,10 +18,7 @@ LOG_MODULE_DECLARE(power);
 extern const struct device __device_start[];
 extern const struct device __device_end[];
 
-/* Indexes into all_devices for devices that support pm,
- * in dependency order (later may depend on earlier).
- */
-static const struct device *pm_devices[CONFIG_PM_MAX_DEVICES];
+extern const struct device *__pm_device_slots_start[];
 
 /* Number of devices successfully suspended. */
 static size_t num_susp;
@@ -77,10 +74,8 @@ static int _pm_devices(uint32_t state)
 				return rc;
 			}
 
-			pm_devices[num_susp] = dev;
+			__pm_device_slots_start[num_susp] = dev;
 			num_susp++;
-			__ASSERT(num_susp < CONFIG_PM_MAX_DEVICES,
-				"Number of pm devices > CONFIG_PM_MAX_DEVICES");
 		}
 	}
 
@@ -107,7 +102,7 @@ void pm_resume_devices(void)
 	size_t i;
 
 	for (i = 0; i < num_susp; i++) {
-		pm_device_state_set(pm_devices[i],
+		pm_device_state_set(__pm_device_slots_start[i],
 				       PM_DEVICE_STATE_ACTIVE,
 				       NULL, NULL);
 	}