Various drivers, mostly in platform/x86 extend the ACPI battery driver
with additional sysfs attributes to implement more UAPIs than are
exposed through ACPI by using various side-channels, like WMI,
nonstandard ACPI or EC communication.

While the created sysfs attributes look similar to the attributes
provided by the powersupply core, there are various deficiencies:

* They don't show up in uevent payload.
* They can't be queried with the standard in-kernel APIs.
* They don't work with triggers.
* The extending driver has to reimplement all of the parsing,
formatting and sysfs display logic.
* Writing a extension driver is completely different from writing a
normal power supply driver.

This extension API avoids all of these issues.
An extension is just a "struct power_supply_ext" with the same kind of
callbacks as in a normal "struct power_supply_desc".

The API is meant to be used via battery_hook_register(), the same way as
the current extensions.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 drivers/power/supply/power_supply.h       |  14 +++
 drivers/power/supply/power_supply_core.c  | 155 ++++++++++++++++++++++++++++--
 drivers/power/supply/power_supply_sysfs.c |  22 ++++-
 include/linux/power_supply.h              |  32 ++++++
 4 files changed, 213 insertions(+), 10 deletions(-)

diff --git a/drivers/power/supply/power_supply.h b/drivers/power/supply/power_supply.h
index 5dabbd895538003096b62d03fdd0201b82b090e6..4c3e602c416cec556173a8eb1a3114c13ded71b7 100644
--- a/drivers/power/supply/power_supply.h
+++ b/drivers/power/supply/power_supply.h
@@ -9,6 +9,8 @@
  *  Modified: 2004, Oct     Szabolcs Gyurko
  */
 
+#include <linux/lockdep.h>
+
 struct device;
 struct device_type;
 struct power_supply;
@@ -17,6 +19,18 @@ extern int power_supply_property_is_writeable(struct power_supply *psy,
 					      enum power_supply_property psp);
 extern bool power_supply_has_property(struct power_supply *psy,
 				      enum power_supply_property psp);
+extern bool power_supply_ext_has_property(const struct power_supply_ext *ext,
+					  enum power_supply_property psp);
+
+struct power_supply_ext_registration {
+	struct list_head list_head;
+	const struct power_supply_ext *ext;
+	void *data;
+};
+
+#define power_supply_for_each_extension(pos, psy) \
+	lockdep_assert_held(&(psy)->extensions_sem); \
+	list_for_each_entry(pos, &(psy)->extensions, list_head)
 
 #ifdef CONFIG_SYSFS
 
diff --git a/drivers/power/supply/power_supply_core.c b/drivers/power/supply/power_supply_core.c
index 502b07468b93dfb7f5a6c2092588d931a7d015f2..bf3054ed034e091adefcdbf98873a108b4c90fde 100644
--- a/drivers/power/supply/power_supply_core.c
+++ b/drivers/power/supply/power_supply_core.c
@@ -81,6 +81,7 @@ static int __power_supply_changed_work(struct device *dev, void *data)
 
 static void power_supply_changed_work(struct work_struct *work)
 {
+	int ret;
 	unsigned long flags;
 	struct power_supply *psy = container_of(work, struct power_supply,
 						changed_work);
@@ -88,6 +89,16 @@ static void power_supply_changed_work(struct work_struct *work)
 	dev_dbg(&psy->dev, "%s\n", __func__);
 
 	spin_lock_irqsave(&psy->changed_lock, flags);
+
+	if (unlikely(psy->update_groups)) {
+		psy->update_groups = false;
+		spin_unlock_irqrestore(&psy->changed_lock, flags);
+		ret = sysfs_update_groups(&psy->dev.kobj, power_supply_dev_type.groups);
+		if (ret)
+			dev_warn(&psy->dev, "failed to update sysfs groups: %pe\n", ERR_PTR(ret));
+		spin_lock_irqsave(&psy->changed_lock, flags);
+	}
+
 	/*
 	 * Check 'changed' here to avoid issues due to race between
 	 * power_supply_changed() and this routine. In worst case
@@ -1196,15 +1207,37 @@ static bool psy_desc_has_property(const struct power_supply_desc *psy_desc,
 	return found;
 }
 
+bool power_supply_ext_has_property(const struct power_supply_ext *psy_ext,
+				   enum power_supply_property psp)
+{
+	bool found = false;
+	int i;
+
+	for (i = 0; i < psy_ext->num_properties; i++) {
+		if (psy_ext->properties[i] == psp) {
+			found = true;
+			break;
+		}
+	}
+
+	return found;
+}
+
 bool power_supply_has_property(struct power_supply *psy,
 			       enum power_supply_property psp)
 {
+	struct power_supply_ext_registration *reg;
+
 	if (psy_desc_has_property(psy->desc, psp))
 		return true;
 
 	if (power_supply_battery_info_has_prop(psy->battery_info, psp))
 		return true;
 
+	power_supply_for_each_extension(reg, psy)
+		if (power_supply_ext_has_property(reg->ext, psp))
+			return true;
+
 	return false;
 }
 
@@ -1212,12 +1245,21 @@ int power_supply_get_property(struct power_supply *psy,
 			    enum power_supply_property psp,
 			    union power_supply_propval *val)
 {
+	struct power_supply_ext_registration *reg;
+
 	if (atomic_read(&psy->use_cnt) <= 0) {
 		if (!psy->initialized)
 			return -EAGAIN;
 		return -ENODEV;
 	}
 
+	guard(rwsem_read)(&psy->extensions_sem);
+
+	power_supply_for_each_extension(reg, psy) {
+		if (power_supply_ext_has_property(reg->ext, psp))
+			return reg->ext->get_property(psy, reg->ext, reg->data, psp, val);
+	}
+
 	if (psy_desc_has_property(psy->desc, psp))
 		return psy->desc->get_property(psy, psp, val);
 	else if (power_supply_battery_info_has_prop(psy->battery_info, psp))
@@ -1231,7 +1273,23 @@ int power_supply_set_property(struct power_supply *psy,
 			    enum power_supply_property psp,
 			    const union power_supply_propval *val)
 {
-	if (atomic_read(&psy->use_cnt) <= 0 || !psy->desc->set_property)
+	struct power_supply_ext_registration *reg;
+
+	if (atomic_read(&psy->use_cnt) <= 0)
+		return -ENODEV;
+
+	guard(rwsem_read)(&psy->extensions_sem);
+
+	power_supply_for_each_extension(reg, psy) {
+		if (power_supply_ext_has_property(reg->ext, psp)) {
+			if (reg->ext->set_property)
+				return reg->ext->set_property(psy, reg->ext, reg->data, psp, val);
+			else
+				return -ENODEV;
+		}
+	}
+
+	if (!psy->desc->set_property)
 		return -ENODEV;
 
 	return psy->desc->set_property(psy, psp, val);
@@ -1241,7 +1299,22 @@ EXPORT_SYMBOL_GPL(power_supply_set_property);
 int power_supply_property_is_writeable(struct power_supply *psy,
 					enum power_supply_property psp)
 {
-	return psy->desc->property_is_writeable && psy->desc->property_is_writeable(psy, psp);
+	struct power_supply_ext_registration *reg;
+
+	power_supply_for_each_extension(reg, psy) {
+		if (power_supply_ext_has_property(reg->ext, psp)) {
+			if (reg->ext->property_is_writeable)
+				return reg->ext->property_is_writeable(psy, reg->ext,
+								       reg->data, psp);
+			else
+				return -ENODEV;
+		}
+	}
+
+	if (!psy->desc->property_is_writeable)
+		return -ENODEV;
+
+	return psy->desc->property_is_writeable(psy, psp);
 }
 
 void power_supply_external_power_changed(struct power_supply *psy)
@@ -1260,6 +1333,67 @@ int power_supply_powers(struct power_supply *psy, struct device *dev)
 }
 EXPORT_SYMBOL_GPL(power_supply_powers);
 
+static int power_supply_update_sysfs_and_hwmon(struct power_supply *psy)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&psy->changed_lock, flags);
+	psy->update_groups = true;
+	spin_unlock_irqrestore(&psy->changed_lock, flags);
+
+	power_supply_changed(psy);
+
+	power_supply_remove_hwmon_sysfs(psy);
+	return power_supply_add_hwmon_sysfs(psy);
+}
+
+int power_supply_register_extension(struct power_supply *psy, const struct power_supply_ext *ext,
+				    void *data)
+{
+	struct power_supply_ext_registration *reg;
+	size_t i;
+
+	guard(rwsem_write)(&psy->extensions_sem);
+
+	power_supply_for_each_extension(reg, psy)
+		if (reg->ext == ext)
+			return -EEXIST;
+
+	for (i = 0; i < ext->num_properties; i++)
+		if (power_supply_has_property(psy, ext->properties[i]))
+			return -EEXIST;
+
+	reg = kmalloc(sizeof(*reg), GFP_KERNEL);
+	if (!reg)
+		return -ENOMEM;
+
+	reg->ext = ext;
+	reg->data = data;
+	list_add(&reg->list_head, &psy->extensions);
+
+	return power_supply_update_sysfs_and_hwmon(psy);
+}
+EXPORT_SYMBOL_GPL(power_supply_register_extension);
+
+void power_supply_unregister_extension(struct power_supply *psy, const struct power_supply_ext *ext)
+{
+	struct power_supply_ext_registration *reg;
+
+	guard(rwsem_write)(&psy->extensions_sem);
+
+	power_supply_for_each_extension(reg, psy) {
+		if (reg->ext == ext) {
+			list_del(&reg->list_head);
+			kfree(reg);
+			power_supply_update_sysfs_and_hwmon(psy);
+			return;
+		}
+	}
+
+	dev_warn(&psy->dev, "Trying to unregister invalid extension");
+}
+EXPORT_SYMBOL_GPL(power_supply_unregister_extension);
+
 static void power_supply_dev_release(struct device *dev)
 {
 	struct power_supply *psy = to_power_supply(dev);
@@ -1414,6 +1548,9 @@ __power_supply_register(struct device *parent,
 	}
 
 	spin_lock_init(&psy->changed_lock);
+	init_rwsem(&psy->extensions_sem);
+	INIT_LIST_HEAD(&psy->extensions);
+
 	rc = device_add(dev);
 	if (rc)
 		goto device_add_failed;
@@ -1426,13 +1563,15 @@ __power_supply_register(struct device *parent,
 	if (rc)
 		goto register_thermal_failed;
 
-	rc = power_supply_create_triggers(psy);
-	if (rc)
-		goto create_triggers_failed;
+	scoped_guard(rwsem_read, &psy->extensions_sem) {
+		rc = power_supply_create_triggers(psy);
+		if (rc)
+			goto create_triggers_failed;
 
-	rc = power_supply_add_hwmon_sysfs(psy);
-	if (rc)
-		goto add_hwmon_sysfs_failed;
+		rc = power_supply_add_hwmon_sysfs(psy);
+		if (rc)
+			goto add_hwmon_sysfs_failed;
+	}
 
 	/*
 	 * Update use_cnt after any uevents (most notably from device_add()).
diff --git a/drivers/power/supply/power_supply_sysfs.c b/drivers/power/supply/power_supply_sysfs.c
index 99bfe1f03eb8326d38c4e2831c9670313b42e425..2cf25bacd7a1bb66e5a72629bffaa6d16bfbf3be 100644
--- a/drivers/power/supply/power_supply_sysfs.c
+++ b/drivers/power/supply/power_supply_sysfs.c
@@ -268,6 +268,23 @@ static ssize_t power_supply_show_enum_with_available(
 	return count;
 }
 
+static ssize_t power_supply_show_charge_behaviour(struct device *dev,
+						  struct power_supply *psy,
+						  union power_supply_propval *value,
+						  char *buf)
+{
+	struct power_supply_ext_registration *reg;
+
+	power_supply_for_each_extension(reg, psy) {
+		if (power_supply_ext_has_property(reg->ext, POWER_SUPPLY_PROP_CHARGE_BEHAVIOUR))
+			return power_supply_charge_behaviour_show(dev, reg->ext->charge_behaviours,
+								  value->intval, buf);
+	}
+
+	return power_supply_charge_behaviour_show(dev, psy->desc->charge_behaviours,
+						  value->intval, buf);
+}
+
 static ssize_t power_supply_format_property(struct device *dev,
 					    bool uevent,
 					    struct device_attribute *attr,
@@ -307,8 +324,7 @@ static ssize_t power_supply_format_property(struct device *dev,
 	case POWER_SUPPLY_PROP_CHARGE_BEHAVIOUR:
 		if (uevent) /* no possible values in uevents */
 			goto default_format;
-		ret = power_supply_charge_behaviour_show(dev, psy->desc->charge_behaviours,
-							 value.intval, buf);
+		ret = power_supply_show_charge_behaviour(dev, psy, &value, buf);
 		break;
 	case POWER_SUPPLY_PROP_MODEL_NAME ... POWER_SUPPLY_PROP_SERIAL_NUMBER:
 		ret = sysfs_emit(buf, "%s\n", value.strval);
@@ -385,6 +401,8 @@ static umode_t power_supply_attr_is_visible(struct kobject *kobj,
 	if (attrno == POWER_SUPPLY_PROP_TYPE)
 		return mode;
 
+	guard(rwsem_read)(&psy->extensions_sem);
+
 	if (power_supply_has_property(psy, attrno)) {
 		if (power_supply_property_is_writeable(psy, attrno) > 0)
 			mode |= S_IWUSR;
diff --git a/include/linux/power_supply.h b/include/linux/power_supply.h
index b98106e1a90f34bce5129317a099f363248342b9..016e44cb3eb5eb7ace01a032661f65a5d81a522f 100644
--- a/include/linux/power_supply.h
+++ b/include/linux/power_supply.h
@@ -15,6 +15,8 @@
 #include <linux/device.h>
 #include <linux/workqueue.h>
 #include <linux/leds.h>
+#include <linux/rwsem.h>
+#include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/notifier.h>
 
@@ -281,6 +283,27 @@ struct power_supply_desc {
 	int use_for_apm;
 };
 
+struct power_supply_ext {
+	u8 charge_behaviours;
+	const enum power_supply_property *properties;
+	size_t num_properties;
+
+	int (*get_property)(struct power_supply *psy,
+			    const struct power_supply_ext *ext,
+			    void *data,
+			    enum power_supply_property psp,
+			    union power_supply_propval *val);
+	int (*set_property)(struct power_supply *psy,
+			    const struct power_supply_ext *ext,
+			    void *data,
+			    enum power_supply_property psp,
+			    const union power_supply_propval *val);
+	int (*property_is_writeable)(struct power_supply *psy,
+				     const struct power_supply_ext *ext,
+				     void *data,
+				     enum power_supply_property psp);
+};
+
 struct power_supply {
 	const struct power_supply_desc *desc;
 
@@ -300,10 +323,13 @@ struct power_supply {
 	struct delayed_work deferred_register_work;
 	spinlock_t changed_lock;
 	bool changed;
+	bool update_groups;
 	bool initialized;
 	bool removing;
 	atomic_t use_cnt;
 	struct power_supply_battery_info *battery_info;
+	struct rw_semaphore extensions_sem; /* protects "extensions" */
+	struct list_head extensions;
 #ifdef CONFIG_THERMAL
 	struct thermal_zone_device *tzd;
 	struct thermal_cooling_device *tcd;
@@ -878,6 +904,12 @@ devm_power_supply_register(struct device *parent,
 extern void power_supply_unregister(struct power_supply *psy);
 extern int power_supply_powers(struct power_supply *psy, struct device *dev);
 
+extern int power_supply_register_extension(struct power_supply *psy,
+					   const struct power_supply_ext *ext,
+					   void *data);
+extern void power_supply_unregister_extension(struct power_supply *psy,
+					      const struct power_supply_ext *ext);
+
 #define to_power_supply(device) container_of(device, struct power_supply, dev)
 
 extern void *power_supply_get_drvdata(struct power_supply *psy);

-- 
2.47.0