[PATCH v3 2/6] ACPI: scan: Add function to fetch dependent of acpi device

[Daniel Scally <djrscally@gmail.com>]

In some ACPI tables we encounter, devices use the _DEP method to assert
a dependence on other ACPI devices as opposed to the OpRegions that the
specification intends. We need to be able to find those devices "from"
the dependee, so add a callback and a wrapper to walk over the
acpi_dep_list and return the dependent ACPI device.

Signed-off-by: Daniel Scally <djrscally@gmail.com>
---
Changes in v3:
	- Switched from a standalone function to a callback passed to
	  acpi_walk_dep_device_list().

 drivers/acpi/scan.c     | 34 ++++++++++++++++++++++++++++++++++
 include/acpi/acpi_bus.h |  1 +
 2 files changed, 35 insertions(+)

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index c9e4190316ef..55626925261c 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -2093,6 +2093,21 @@ static void acpi_bus_attach(struct acpi_device *device, bool first_pass)
 		device->handler->hotplug.notify_online(device);
 }
 
+static int __acpi_dev_get_dependent_dev(struct acpi_dep_data *dep, void *data)
+{
+	struct acpi_device *adev;
+	int ret;
+
+	ret = acpi_bus_get_device(dep->consumer, &adev);
+	if (ret)
+		/* If we don't find an adev then we want to continue parsing */
+		return 0;
+
+	*(struct acpi_device **)data = adev;
+
+	return 1;
+}
+
 static int __acpi_dev_flag_dependency_met(struct acpi_dep_data *dep,
 					  void *data)
 {
@@ -2145,6 +2160,25 @@ void acpi_dev_flag_dependency_met(acpi_handle handle)
 }
 EXPORT_SYMBOL_GPL(acpi_dev_flag_dependency_met);
 
+/**
+ * acpi_dev_get_dependent_dev - Return ACPI device dependent on @adev
+ * @adev: Pointer to the dependee device
+ *
+ * Returns the first &struct acpi_device which declares itself dependent on
+ * @adev via the _DEP buffer, parsed from the acpi_dep_list.
+ */
+struct acpi_device *
+acpi_dev_get_dependent_dev(struct acpi_device *supplier)
+{
+	struct acpi_device *adev = NULL;
+
+	acpi_walk_dep_device_list(supplier->handle,
+				  __acpi_dev_get_dependent_dev, &adev);
+
+	return adev;
+}
+EXPORT_SYMBOL_GPL(acpi_dev_get_dependent_dev);
+
 /**
  * acpi_bus_scan - Add ACPI device node objects in a given namespace scope.
  * @handle: Root of the namespace scope to scan.
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index 91172af3a04d..5b14a9ae4ed5 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -690,6 +690,7 @@ static inline bool acpi_device_can_poweroff(struct acpi_device *adev)
 bool acpi_dev_hid_uid_match(struct acpi_device *adev, const char *hid2, const char *uid2);
 
 void acpi_dev_flag_dependency_met(acpi_handle handle);
+struct acpi_device *acpi_dev_get_dependent_dev(struct acpi_device *supplier);
 struct acpi_device *
 acpi_dev_get_next_match_dev(struct acpi_device *adev, const char *hid, const char *uid, s64 hrv);
 struct acpi_device *
-- 
2.25.1