ACPI / utils: Add acpi_dev_present()

There's an idiom in use by 7 Linux drivers to detect the presence of a
particular ACPI HID by walking the namespace with acpi_get_devices().
The callback passed to acpi_get_devices() is mostly identical across
the drivers, leading to lots of duplicate code.

Add acpi_dev_present(), the ACPI equivalent to pci_dev_present(),
allowing us to deduplicate all that boilerplate in the drivers.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/internal.h

@@ -86,6 +86,14 @@ bool acpi_scan_is_offline(struct acpi_device *adev, bool uevent);
 #define ACPI_STA_DEFAULT (ACPI_STA_DEVICE_PRESENT | ACPI_STA_DEVICE_ENABLED | \
 			  ACPI_STA_DEVICE_UI | ACPI_STA_DEVICE_FUNCTIONING)
 
+extern struct list_head acpi_bus_id_list;
+
+struct acpi_device_bus_id{
+	char bus_id[15];
+	unsigned int instance_no;
+	struct list_head node;
+};
+
 int acpi_device_add(struct acpi_device *device,
 		    void (*release)(struct device *));
 void acpi_init_device_object(struct acpi_device *device, acpi_handle handle,

drivers/acpi/scan.c

@@ -39,7 +39,7 @@ 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);
+LIST_HEAD(acpi_bus_id_list);
 static DEFINE_MUTEX(acpi_scan_lock);
 static LIST_HEAD(acpi_scan_handlers_list);
 DEFINE_MUTEX(acpi_device_lock);
@@ -52,12 +52,6 @@ struct acpi_dep_data {
 	acpi_handle slave;
 };
 
-struct acpi_device_bus_id{
-	char bus_id[15];
-	unsigned int instance_no;
-	struct list_head node;
-};
-
 void acpi_scan_lock_acquire(void)
 {
 	mutex_lock(&acpi_scan_lock);

drivers/acpi/utils.c

@@ -29,6 +29,7 @@
 #include <linux/dynamic_debug.h>
 
 #include "internal.h"
+#include "sleep.h"
 
 #define _COMPONENT		ACPI_BUS_COMPONENT
 ACPI_MODULE_NAME("utils");
@@ -709,6 +710,36 @@ bool acpi_check_dsm(acpi_handle handle, const u8 *uuid, int rev, u64 funcs)
 }
 EXPORT_SYMBOL(acpi_check_dsm);
 
+/**
+ * acpi_dev_present - Detect presence of a given ACPI device in the system.
+ * @hid: Hardware ID of the device.
+ *
+ * Return %true if the device was present at the moment of invocation.
+ * Note that if the device is pluggable, it may since have disappeared.
+ *
+ * For this function to work, acpi_bus_scan() must have been executed
+ * which happens in the subsys_initcall() subsection. Hence, do not
+ * call from a subsys_initcall() or earlier (use acpi_get_devices()
+ * instead). Calling from module_init() is fine (which is synonymous
+ * with device_initcall()).
+ */
+bool acpi_dev_present(const char *hid)
+{
+	struct acpi_device_bus_id *acpi_device_bus_id;
+	bool found = false;
+
+	mutex_lock(&acpi_device_lock);
+	list_for_each_entry(acpi_device_bus_id, &acpi_bus_id_list, node)
+		if (!strcmp(acpi_device_bus_id->bus_id, hid)) {
+			found = true;
+			break;
+		}
+	mutex_unlock(&acpi_device_lock);
+
+	return found;
+}
+EXPORT_SYMBOL(acpi_dev_present);
+
 /*
  * acpi_backlight= handling, this is done here rather then in video_detect.c
  * because __setup cannot be used in modules.

include/acpi/acpi_bus.h

@@ -87,6 +87,8 @@ acpi_evaluate_dsm_typed(acpi_handle handle, const u8 *uuid, int rev, int func,
 	  .package.elements = (eles)			\
 	}
 
+bool acpi_dev_present(const char *hid);
+
 #ifdef CONFIG_ACPI
 
 #include <linux/proc_fs.h>