[RFC PATCH V2] ACPI: Add _DEP(Operation Region Dependencies) support to fix battery issue on the Asus T100TA

[Lan Tianyu]

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_dep_list and adding dep_unmet count in the struct
acpi_device. During ACPI namespace scan, create struct acpi_dep_data for a
valid pair of master (device pointed to by _DEP)/slave(device with _DEP), record
master's and slave's ACPI handle in it and put it into acpi_dep_list. The dep_unmet
count will increase by one if there is a device under its _DEP. Driver's probe() should
return EPROBE_DEFER when find dep_unmet larger than 0. When I2C operation
region handler is installed, remove all struct acpi_dep_data on the acpi_dep_list
whose master is pointed to I2C host controller and decrease slave's dep_unmet.
When dep_unmet decreases to 0, all _DEP conditions are met and then do acpi_bus_attach()
for the device in order to resolve battery _STA issue on the Asus T100TA.

Signed-off-by: Lan Tianyu <tianyu.lan@xxxxxxxxx>
---
Change since V1:
	Rework struct acpi_dep_data, record master and slave's ACPI handle.
Rename dep_present with dep_unmet and make it as a count. Increase dep_unmet
during bootup and decrease it when associated operation region is installed.

 drivers/acpi/scan.c     | 91 +++++++++++++++++++++++++++++++++++++++++++++++++
 drivers/i2c/i2c-core.c  |  1 +
 include/acpi/acpi_bus.h |  1 +
 include/linux/acpi.h    |  3 ++
 4 files changed, 96 insertions(+)

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 4da55d8..bfa9c77 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -36,6 +36,8 @@ bool acpi_force_hot_remove;
 
 static const char *dummy_hid = "device";
 
+static LIST_HEAD(acpi_dep_list);
+static DEFINE_MUTEX(acpi_dep_list_lock);
 static LIST_HEAD(acpi_bus_id_list);
 static DEFINE_MUTEX(acpi_scan_lock);
 static LIST_HEAD(acpi_scan_handlers_list);
@@ -43,6 +45,12 @@ 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;
+	acpi_handle master;
+	acpi_handle slave;
+};
+
 struct acpi_device_bus_id{
 	char bus_id[15];
 	unsigned int instance_no;
@@ -2121,6 +2129,63 @@ 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;
+	struct acpi_handle_list dep_devices;
+	struct acpi_device_info *info;
+	acpi_status status;
+	int i, skip;
+
+	if (!acpi_has_method(adev->handle, "_DEP"))
+		return;
+
+	status = acpi_evaluate_reference(adev->handle, "_DEP", NULL,
+					&dep_devices);
+	if (ACPI_FAILURE(status)) {
+		dev_err(&adev->dev, "Failed to evaluate _DEP.\n");
+		return;
+	}
+
+	for (i = 0; i < dep_devices.count; i++) {
+
+		status = acpi_get_object_info(dep_devices.handles[i], &info);
+		if (ACPI_FAILURE(status)) {
+			dev_err(&adev->dev, "Error reading device info\n");
+			continue;
+		}
+
+		/*
+		 * Skip the dependency of Windows System Power
+		 * Management Controller
+		 */
+		if (info->valid & ACPI_VALID_HID
+		    && !strcmp(info->hardware_id.string, "INT3396"))
+			skip = 1;
+		else
+			skip = 0;
+
+		kfree(info);
+
+		if (skip)
+			continue;
+
+		dep = kzalloc(sizeof(struct acpi_dep_data), GFP_KERNEL);
+		if (!dep) {
+			dev_err(&adev->dev, "Not enough memory for _DEP list entry.\n");
+			return;
+		}
+
+		dep->master = dep_devices.handles[i];
+		dep->slave  = adev->handle;
+		adev->dep_unmet++;
+
+		mutex_lock(&acpi_dep_list_lock);
+		list_add_tail(&dep->node , &acpi_dep_list);
+		mutex_unlock(&acpi_dep_list_lock);
+	}
+}
+
 static acpi_status acpi_bus_check_add(acpi_handle handle, u32 lvl_not_used,
 				      void *not_used, void **return_value)
 {
@@ -2147,6 +2212,7 @@ 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)
@@ -2267,6 +2333,31 @@ static void acpi_bus_attach(struct acpi_device *device)
 		device->handler->hotplug.notify_online(device);
 }
 
+int acpi_walk_dep_device_list(acpi_handle handle)
+{
+	struct acpi_dep_data *dep, *tmp;
+	struct acpi_device *adev;
+
+	mutex_lock(&acpi_dep_list_lock);
+	list_for_each_entry_safe(dep, tmp, &acpi_dep_list, node) {
+		if (dep->master == handle) {
+			acpi_bus_get_device(dep->slave, &adev);
+			if (!adev)
+				continue;
+
+			adev->dep_unmet--;
+			if (!adev->dep_unmet)
+				acpi_bus_attach(adev);
+			list_del(&dep->node);
+			kfree(dep);
+		}
+	}
+	mutex_unlock(&acpi_dep_list_lock);
+
+	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-core.c b/drivers/i2c/i2c-core.c
index 126e182..d5495ca 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -402,6 +402,7 @@ static int acpi_i2c_install_space_handler(struct i2c_adapter *adapter)
 		return -ENOMEM;
 	}
 
+	acpi_walk_dep_device_list(handle);
 	return 0;
 }
 
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index 98cd723..269f068 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -367,6 +367,7 @@ struct acpi_device {
 	void *driver_data;
 	struct device dev;
 	unsigned int physical_node_count;
+	unsigned int dep_unmet;
 	struct list_head physical_node_list;
 	struct mutex physical_node_lock;
 	void (*remove)(struct acpi_device *);
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 2b9c235..cec5f55 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -428,6 +428,7 @@ extern bool acpi_driver_match_device(struct device *dev,
 				     const struct device_driver *drv);
 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(acpi_handle handle);
 
 #define ACPI_PTR(_ptr)	(_ptr)
 
@@ -446,6 +447,8 @@ 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(acpi_handle handle) { }
+
 static inline int early_acpi_boot_init(void)
 {
 	return 0;
-- 
1.8.4.rc0.1.g8f6a3e5.dirty

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