ACPI: utils: Add api to read _SUB from ACPI

Add a wrapper function to read the _SUB string from ACPI.

Signed-off-by: Stefan Binding <[email protected]>
Acked-by: Rafael J. Wysocki <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mark Brown <[email protected]>

1 files changed, 38 insertions, 0 deletions

diff --git a/drivers/acpi/utils.c b/drivers/acpi/utils.c
index 3a9773a09e19..5a7b8065e77f 100644
--- a/drivers/acpi/utils.c
+++ b/drivers/acpi/utils.c
@@ -291,6 +291,44 @@ int acpi_get_local_address(acpi_handle handle, u32 *addr)
 }
 EXPORT_SYMBOL(acpi_get_local_address);
 
+#define ACPI_MAX_SUB_BUF_SIZE	9
+
+const char *acpi_get_subsystem_id(acpi_handle handle)
+{
+	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
+	union acpi_object *obj;
+	acpi_status status;
+	const char *sub;
+	size_t len;
+
+	status = acpi_evaluate_object(handle, METHOD_NAME__SUB, NULL, &buffer);
+	if (ACPI_FAILURE(status)) {
+		acpi_handle_debug(handle, "Reading ACPI _SUB failed: %#x\n", status);
+		return ERR_PTR(-ENODATA);
+	}
+
+	obj = buffer.pointer;
+	if (obj->type == ACPI_TYPE_STRING) {
+		len = strlen(obj->string.pointer);
+		if (len < ACPI_MAX_SUB_BUF_SIZE && len > 0) {
+			sub = kstrdup(obj->string.pointer, GFP_KERNEL);
+			if (!sub)
+				sub = ERR_PTR(-ENOMEM);
+		} else {
+			acpi_handle_err(handle, "ACPI _SUB Length %zu is Invalid\n", len);
+			sub = ERR_PTR(-ENODATA);
+		}
+	} else {
+		acpi_handle_warn(handle, "Warning ACPI _SUB did not return a string\n");
+		sub = ERR_PTR(-ENODATA);
+	}
+
+	acpi_os_free(buffer.pointer);
+
+	return sub;
+}
+EXPORT_SYMBOL_GPL(acpi_get_subsystem_id);
+
 acpi_status
 acpi_evaluate_reference(acpi_handle handle,
 			acpi_string pathname,