[PATCH 14/18] acpi: utils: Add function to fetch dependent acpi_devices

[Daniel Scally <djrscally@xxxxxxxxx>]

ACPI devices declare themselves dependent on other devices via the _DEP
buffer. Fetching the dependee from dependent is a matter of parsing
_DEP, but currently there's no method to fetch dependent from dependee.
Add one, so we can parse sensors dependent on a PMIC from the PMIC's
acpi_driver.

Signed-off-by: Daniel Scally <djrscally@xxxxxxxxx>
---
Changes since RFC v3:

	- Patch introduced

 drivers/acpi/utils.c    | 68 +++++++++++++++++++++++++++++++++++++++++
 include/acpi/acpi_bus.h |  2 ++
 2 files changed, 70 insertions(+)

diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
index c177165c8db2..7099529121db 100644
--- a/drivers/acpi/utils.c
+++ b/drivers/acpi/utils.c
@@ -807,6 +807,52 @@ static int acpi_dev_match_cb(struct device *dev, const void *data)
 	return hrv == match->hrv;
 }
 
+static int acpi_dev_match_by_dep(struct device *dev, const void *data)
+{
+	struct acpi_device *adev = to_acpi_device(dev);
+	const struct acpi_device *dependee = data;
+	struct acpi_handle_list dep_handles;
+	struct acpi_device *candidate;
+	acpi_handle handle;
+	acpi_status status;
+	unsigned int i;
+	int ret;
+
+	handle = adev->handle;
+
+	if (!acpi_has_method(handle, "_DEP"))
+		return 0;
+
+	status = acpi_evaluate_reference(handle, "_DEP", NULL, &dep_handles);
+	if (ACPI_FAILURE(status))
+		return 0;
+
+	for (i = 0; i < dep_handles.count; i++) {
+		struct acpi_device_info *info;
+
+		status = acpi_get_object_info(dep_handles.handles[i], &info);
+		if (ACPI_FAILURE(status))
+			continue;
+
+		if (info->valid & ACPI_VALID_HID) {
+			ret = acpi_bus_get_device(dep_handles.handles[i], &candidate);
+			if (ret || !candidate) {
+				kfree(info);
+				continue;
+			}
+
+			if (candidate == dependee) {
+				acpi_dev_put(candidate);
+				kfree(info);
+				return 1;
+			}
+
+			kfree(info);
+		}
+	}
+	return 0;
+}
+
 /**
  * acpi_dev_present - Detect that a given ACPI device is present
  * @hid: Hardware ID of the device.
@@ -842,6 +888,28 @@ bool acpi_dev_present(const char *hid, const char *uid, s64 hrv)
 }
 EXPORT_SYMBOL(acpi_dev_present);
 
+/**
+ * acpi_dev_get_next_dep_dev - Return next ACPI device dependent on input dev
+ * @adev: Pointer to the dependee device
+ * @prev: Pointer to the previous dependent device (or NULL for first match)
+ *
+ * Return the next ACPI device which declares itself dependent on @adev in
+ * the _DEP buffer.
+ *
+ * The caller is responsible to call put_device() on the returned device.
+ */
+struct acpi_device *acpi_dev_get_next_dep_dev(struct acpi_device *adev,
+					      struct acpi_device *prev)
+{
+	struct device *start = prev ? &prev->dev : NULL;
+	struct device *dev;
+
+	dev = bus_find_device(&acpi_bus_type, start, adev, acpi_dev_match_by_dep);
+
+	return dev ? to_acpi_device(dev) : NULL;
+}
+EXPORT_SYMBOL(acpi_dev_get_next_dep_dev);
+
 /**
  * acpi_dev_get_next_match_dev - Return the next match of ACPI device
  * @adev: Pointer to the previous acpi_device matching this hid, uid and hrv
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index 0a028ba967d3..f5dfeb030b9c 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -688,6 +688,8 @@ 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);
 
+struct acpi_device *
+acpi_dev_get_next_dep_dev(struct acpi_device *adev, struct acpi_device *prev);
 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