[PATCH 1/2] ACPI: sbs: add battery hook mechanism for SBS-registered batteries

[Jordan Brough <jordan@brough.org>]

drivers/acpi/battery.c provides a battery_hook_register()/unregister()
mechanism that lets other drivers (e.g. hwmon drivers exposing vendor-
specific charge control) attach extra power_supply properties to an
ACPI Control Method Battery (HID PNP0C0A, "CmBatt").

Some machines instead expose their battery through the ACPI Smart
Battery System (HID ACPI0002, "SBS") driver in drivers/acpi/sbs.c,
which has no equivalent hook point. On these machines a hwmon driver
has no supported way to attach additional properties to the battery's
power_supply device.

Add a parallel sbs_battery_hook_register()/unregister() mechanism to
drivers/acpi/sbs.c, mirroring the existing CmBatt hook API in name and
behavior so that callers can support both battery registration paths
symmetrically. This is purely additive: no existing hook consumer or
code path in drivers/acpi/battery.c is touched, and sbs.c's own
behavior is unchanged for any driver that does not call the new API.

This is a prerequisite for hwmon/applesmc gaining
charge_control_end_threshold support, since the Intel MacBook hardware
being targeted registers its battery via SBS, not CmBatt.

Signed-off-by: Jordan Brough <jordan@brough.org>
---
 drivers/acpi/sbs.c     | 147 ++++++++++++++++++++++++++++++++++++++++-
 include/acpi/battery.h |  16 +++++
 2 files changed, 162 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/sbs.c b/drivers/acpi/sbs.c
index 86b7c797585..305bf62eae3 100644
--- a/drivers/acpi/sbs.c
+++ b/drivers/acpi/sbs.c
@@ -10,6 +10,7 @@
 #define pr_fmt(fmt) "ACPI: " fmt
 
 #include <linux/init.h>
+#include <linux/list.h>
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
@@ -54,6 +55,7 @@ struct acpi_battery {
 	struct power_supply *bat;
 	struct power_supply_desc bat_desc;
 	struct acpi_sbs *sbs;
+	struct list_head list;		/* node in sbs_hook_battery_list */
 	unsigned long update_time;
 	char name[8];
 	char manufacturer_name[ACPI_SBS_BLOCK_MAX];
@@ -518,6 +520,145 @@ static int acpi_battery_read(struct acpi_battery *battery)
 	return result;
 }
 
+/*
+ * Battery hook support, mirroring the mechanism in drivers/acpi/battery.c
+ * for batteries registered there. That mechanism only sees batteries
+ * added via drivers/acpi/battery.c, not the ones this driver registers,
+ * so drivers wanting to attach optional functionality (e.g. an extra
+ * power_supply_ext) to an SBS battery need this separate copy; see the
+ * comment above the declarations in include/acpi/battery.h.
+ */
+static LIST_HEAD(sbs_hook_list);
+static LIST_HEAD(sbs_hook_battery_list);
+static DEFINE_MUTEX(sbs_hook_mutex);
+
+static void sbs_battery_hook_unregister_unlocked(struct acpi_battery_hook *hook)
+{
+	struct acpi_battery *battery;
+
+	/*
+	 * In order to remove a hook, we first need to
+	 * de-register all the batteries that are registered.
+	 */
+	list_for_each_entry(battery, &sbs_hook_battery_list, list) {
+		if (!hook->remove_battery(battery->bat, hook))
+			power_supply_changed(battery->bat);
+	}
+	list_del_init(&hook->list);
+}
+
+void sbs_battery_hook_unregister(struct acpi_battery_hook *hook)
+{
+	mutex_lock(&sbs_hook_mutex);
+	/*
+	 * Ignore already unregistered battery hooks. This might happen
+	 * if a battery hook was previously unloaded due to an error when
+	 * adding a new battery.
+	 */
+	if (!list_empty(&hook->list))
+		sbs_battery_hook_unregister_unlocked(hook);
+	mutex_unlock(&sbs_hook_mutex);
+}
+EXPORT_SYMBOL_GPL(sbs_battery_hook_unregister);
+
+void sbs_battery_hook_register(struct acpi_battery_hook *hook)
+{
+	struct acpi_battery *battery;
+
+	mutex_lock(&sbs_hook_mutex);
+	list_add(&hook->list, &sbs_hook_list);
+	/*
+	 * Now that the driver is registered, we need
+	 * to notify the hook that a battery is available
+	 * for each battery, so that the driver may add
+	 * its attributes.
+	 */
+	list_for_each_entry(battery, &sbs_hook_battery_list, list) {
+		if (hook->add_battery(battery->bat, hook)) {
+			/*
+			 * If a add-battery returns non-zero,
+			 * the registration of the hook has failed,
+			 * and we will not add it to the list of loaded
+			 * hooks.
+			 */
+			pr_err("hook failed to load: %s", hook->name);
+			sbs_battery_hook_unregister_unlocked(hook);
+			goto end;
+		}
+
+		power_supply_changed(battery->bat);
+	}
+	pr_info("new hook: %s\n", hook->name);
+end:
+	mutex_unlock(&sbs_hook_mutex);
+}
+EXPORT_SYMBOL_GPL(sbs_battery_hook_register);
+
+static void devm_sbs_battery_hook_unregister(void *data)
+{
+	struct acpi_battery_hook *hook = data;
+
+	sbs_battery_hook_unregister(hook);
+}
+
+int devm_sbs_battery_hook_register(struct device *dev, struct acpi_battery_hook *hook)
+{
+	sbs_battery_hook_register(hook);
+
+	return devm_add_action_or_reset(dev, devm_sbs_battery_hook_unregister, hook);
+}
+EXPORT_SYMBOL_GPL(devm_sbs_battery_hook_register);
+
+/*
+ * This function gets called right after the battery sysfs
+ * attributes have been added, so that the drivers that
+ * define custom sysfs attributes can add their own.
+ */
+static void sbs_battery_hook_add_battery(struct acpi_battery *battery)
+{
+	struct acpi_battery_hook *hook_node, *tmp;
+
+	mutex_lock(&sbs_hook_mutex);
+	INIT_LIST_HEAD(&battery->list);
+	list_add(&battery->list, &sbs_hook_battery_list);
+	/*
+	 * Since we added a new battery to the list, we need to
+	 * iterate over the hooks and call add_battery for each
+	 * hook that was registered. This usually happens
+	 * when a battery gets hotplugged or initialized
+	 * during the battery module initialization.
+	 */
+	list_for_each_entry_safe(hook_node, tmp, &sbs_hook_list, list) {
+		if (hook_node->add_battery(battery->bat, hook_node)) {
+			/*
+			 * The notification of the hook has failed, to
+			 * prevent further errors we will unload the hook.
+			 */
+			pr_err("error in hook, unloading: %s",
+			       hook_node->name);
+			sbs_battery_hook_unregister_unlocked(hook_node);
+		}
+	}
+	mutex_unlock(&sbs_hook_mutex);
+}
+
+static void sbs_battery_hook_remove_battery(struct acpi_battery *battery)
+{
+	struct acpi_battery_hook *hook;
+
+	mutex_lock(&sbs_hook_mutex);
+	/*
+	 * Before removing the hook, we need to remove all
+	 * custom attributes from the battery.
+	 */
+	list_for_each_entry(hook, &sbs_hook_list, list) {
+		hook->remove_battery(battery->bat, hook);
+	}
+	/* Then, just remove the battery from the list */
+	list_del(&battery->list);
+	mutex_unlock(&sbs_hook_mutex);
+}
+
 /* Smart Battery */
 static int acpi_battery_add(struct acpi_sbs *sbs, int id)
 {
@@ -555,6 +696,8 @@ static int acpi_battery_add(struct acpi_sbs *sbs, int id)
 		goto end;
 	}
 
+	sbs_battery_hook_add_battery(battery);
+
       end:
 	pr_info("%s [%s]: Battery Slot [%s] (battery %s)\n",
 	       ACPI_SBS_DEVICE_NAME, acpi_device_bid(sbs->device),
@@ -566,8 +709,10 @@ static void acpi_battery_remove(struct acpi_sbs *sbs, int id)
 {
 	struct acpi_battery *battery = &sbs->battery[id];
 
-	if (battery->bat)
+	if (battery->bat) {
+		sbs_battery_hook_remove_battery(battery);
 		power_supply_unregister(battery->bat);
+	}
 }
 
 static int acpi_charger_add(struct acpi_sbs *sbs)
diff --git a/include/acpi/battery.h b/include/acpi/battery.h
index c93f16dfb94..ddbfa4ed135 100644
--- a/include/acpi/battery.h
+++ b/include/acpi/battery.h
@@ -18,8 +18,24 @@ struct acpi_battery_hook {
 	struct list_head list;
 };
 
+/*
+ * battery_hook_register() and friends only see batteries registered by
+ * drivers/acpi/battery.c, the ACPI Control Method Battery driver (ACPI HID
+ * "PNP0C0A"). Batteries registered by drivers/acpi/sbs.c, the ACPI Smart
+ * Battery System driver (ACPI HID "ACPI0002", common on hardware with
+ * SMBus/SBS fuel-gauge chips such as many Intel MacBooks), are invisible
+ * to them; use the sbs_battery_hook_* equivalents below for those. A
+ * caller wanting to support both kinds of hardware needs two separate
+ * struct acpi_battery_hook instances, one per registration call, since a
+ * given instance's embedded list node can only belong to one list at a
+ * time.
+ */
 void battery_hook_register(struct acpi_battery_hook *hook);
 void battery_hook_unregister(struct acpi_battery_hook *hook);
 int devm_battery_hook_register(struct device *dev, struct acpi_battery_hook *hook);
 
+void sbs_battery_hook_register(struct acpi_battery_hook *hook);
+void sbs_battery_hook_unregister(struct acpi_battery_hook *hook);
+int devm_sbs_battery_hook_register(struct device *dev, struct acpi_battery_hook *hook);
+
 #endif
-- 
2.55.0