[RFC PATCH] ACPI: Add _DEP(Operation Region Dependencies) support to fix battery issue on the Asus T100TA

[Lan Tianyu <tianyu.lan@intel.com>]

ACPI 5.0 introduces _DEP to designate device objects that OSPM should
assign a higher priority in start ordering due to future operation region
accesses.

On Asus T100TA, ACPI battery info are read from a I2C slave device via
I2C operation region. Before I2C operation region handler is installed,
battery _STA always returns 0. There is a _DEP method of designating
start order under battery device node.

This patch is to implement _DEP feature to fix battery issue on the Asus T100TA.
Introducing acpi_bus_dep_device_list and adding dep_present flags in the struct
acpi_device. During ACPI namespace scan, all devices with _DEP support will be put
into the new list and those devices' dep_present flag will be set. Driver's probe()
should return EPROBE_DEFER when find dep_present is set. When I2C operation
region handler is installed, check all devices on the new list. Remove the one from
list if _DEP condition is met and clear its dep_present flag and do acpi_bus_attch()
for the device in order to resolve battery _STA issue on the Asus T100TA.

Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
---
 drivers/acpi/battery.c  |  4 +++
 drivers/acpi/scan.c     | 84 +++++++++++++++++++++++++++++++++++++++++++++++++
 drivers/i2c/i2c-acpi.c  |  1 +
 include/acpi/acpi_bus.h |  2 ++
 include/linux/acpi.h    |  3 ++
 5 files changed, 94 insertions(+)

diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
index 1c162e7..c0a68ce 100644
--- a/drivers/acpi/battery.c
+++ b/drivers/acpi/battery.c
@@ -1194,6 +1194,10 @@ static int acpi_battery_add(struct acpi_device *device)
 
 	if (!device)
 		return -EINVAL;
+
+	if (device->dep_present)
+		return -EPROBE_DEFER;
+
 	battery = kzalloc(sizeof(struct acpi_battery), GFP_KERNEL);
 	if (!battery)
 		return -ENOMEM;
diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 3bf7764..a26dbb3 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -36,6 +36,7 @@ bool acpi_force_hot_remove;
 
 static const char *dummy_hid = "device";
 
+static LIST_HEAD(acpi_bus_dep_device_list);
 static LIST_HEAD(acpi_bus_id_list);
 static DEFINE_MUTEX(acpi_scan_lock);
 static LIST_HEAD(acpi_scan_handlers_list);
@@ -43,6 +44,11 @@ DEFINE_MUTEX(acpi_device_lock);
 LIST_HEAD(acpi_wakeup_device_list);
 static DEFINE_MUTEX(acpi_hp_context_lock);
 
+struct acpi_dep_data {
+	struct list_head node;
+	struct acpi_device *adev;
+};
+
 struct acpi_device_bus_id{
 	char bus_id[15];
 	unsigned int instance_no;
@@ -2048,6 +2054,32 @@ static void acpi_scan_init_hotplug(struct acpi_device *adev)
 	}
 }
 
+static void acpi_device_dep_initialize(struct acpi_device * adev)
+{
+	struct acpi_dep_data *dep;
+	acpi_status status;
+
+	if (!acpi_has_method(adev->handle, "_DEP"))
+		return;
+
+	status = acpi_evaluate_reference(adev->handle, "_DEP", NULL,
+					&adev->dep_devices);
+	if (ACPI_FAILURE(status)) {
+		dev_err(&adev->dev, "Fail to evaluate _DEP.\n");
+		return;
+	}
+
+	dep = kzalloc(sizeof(struct acpi_dep_data), GFP_KERNEL);
+	if (!dep) {
+		dev_err(&adev->dev, "Memory allocation error.\n");
+		return;
+	}
+
+	dep->adev = adev;
+	adev->dep_present = true;
+	list_add_tail(&dep->node , &acpi_bus_dep_device_list);
+}
+
 static acpi_status acpi_bus_check_add(acpi_handle handle, u32 lvl_not_used,
 				      void *not_used, void **return_value)
 {
@@ -2074,6 +2106,7 @@ static acpi_status acpi_bus_check_add(acpi_handle handle, u32 lvl_not_used,
 		return AE_CTRL_DEPTH;
 
 	acpi_scan_init_hotplug(device);
+	acpi_device_dep_initialize(device);
 
  out:
 	if (!*return_value)
@@ -2191,6 +2224,57 @@ static void acpi_bus_attach(struct acpi_device *device)
 		acpi_bus_attach(child);
 }
 
+static int acpi_device_dep_check(struct acpi_device *adev)
+{
+	struct acpi_device *dep_adev;
+	struct acpi_device_physical_node *pn;
+	int i;
+
+	for (i = 0; i < adev->dep_devices.count; i++) {
+		dep_adev = acpi_bus_get_acpi_device(
+				adev->dep_devices.handles[i]);
+
+		if (!dep_adev)
+			return -ENODEV;
+
+		/* Check acpi device driver probing */
+		if (dep_adev->dev.driver)
+			continue;
+
+		if (!dep_adev->physical_node_count)
+			return -ENODEV;
+
+		/* Check physcial device node driver probing */
+		mutex_lock(&dep_adev->physical_node_lock);
+		list_for_each_entry(pn, &dep_adev->physical_node_list, node) {
+			if (pn->dev->driver) {
+				mutex_unlock(&dep_adev->physical_node_lock);
+				continue;
+			}
+		}
+		mutex_unlock(&dep_adev->physical_node_lock);
+		return -EFAULT;
+	}
+
+	return 0;
+}
+
+int acpi_walk_dep_device_list(void)
+{
+	struct acpi_dep_data *dep, *tmp;
+
+	list_for_each_entry_safe(dep, tmp, &acpi_bus_dep_device_list, node) {
+		if (!acpi_device_dep_check(dep->adev)) {
+			dep->adev->dep_present = false;
+			acpi_bus_attach(dep->adev);
+			list_del(&dep->node);
+			kfree(dep);
+		}
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(acpi_walk_dep_device_list);
+
 /**
  * acpi_bus_scan - Add ACPI device node objects in a given namespace scope.
  * @handle: Root of the namespace scope to scan.
diff --git a/drivers/i2c/i2c-acpi.c b/drivers/i2c/i2c-acpi.c
index 0dbc18c..fdc8dc8 100644
--- a/drivers/i2c/i2c-acpi.c
+++ b/drivers/i2c/i2c-acpi.c
@@ -339,6 +339,7 @@ int acpi_i2c_install_space_handler(struct i2c_adapter *adapter)
 		return -ENOMEM;
 	}
 
+	acpi_walk_dep_device_list();
 	return 0;
 }
 
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index c1c9de1..c1e7055 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -357,7 +357,9 @@ struct acpi_device {
 	struct acpi_hotplug_context *hp;
 	struct acpi_driver *driver;
 	void *driver_data;
+	bool dep_present;
 	struct device dev;
+	struct acpi_handle_list dep_devices;
 	unsigned int physical_node_count;
 	struct list_head physical_node_list;
 	struct mutex physical_node_lock;
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 807cbc4..c9a504b 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -431,6 +431,7 @@ static inline bool acpi_driver_match_device(struct device *dev,
 
 int acpi_device_uevent_modalias(struct device *, struct kobj_uevent_env *);
 int acpi_device_modalias(struct device *, char *, int);
+int acpi_walk_dep_device_list(void);
 
 #define ACPI_PTR(_ptr)	(_ptr)
 
@@ -449,6 +450,8 @@ static inline const char *acpi_dev_name(struct acpi_device *adev)
 
 static inline void acpi_early_init(void) { }
 
+static inline int acpi_walk_dep_device_list(void) { }
+
 static inline int early_acpi_boot_init(void)
 {
 	return 0;
-- 
1.8.4.rc0.1.g8f6a3e5.dirty