v4.19.13 snapshot.
diff --git a/sound/ac97_bus.c b/sound/ac97_bus.c
new file mode 100644
index 0000000..52e4bc5
--- /dev/null
+++ b/sound/ac97_bus.c
@@ -0,0 +1,113 @@
+/*
+ * Linux driver model AC97 bus interface
+ *
+ * Author: Nicolas Pitre
+ * Created: Jan 14, 2005
+ * Copyright: (C) MontaVista Software Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/device.h>
+#include <linux/string.h>
+#include <sound/ac97_codec.h>
+
+/*
+ * snd_ac97_check_id() - Reads and checks the vendor ID of the device
+ * @ac97: The AC97 device to check
+ * @id: The ID to compare to
+ * @id_mask: Mask that is applied to the device ID before comparing to @id
+ *
+ * If @id is 0 this function returns true if the read device vendor ID is
+ * a valid ID. If @id is non 0 this functions returns true if @id
+ * matches the read vendor ID. Otherwise the function returns false.
+ */
+static bool snd_ac97_check_id(struct snd_ac97 *ac97, unsigned int id,
+ unsigned int id_mask)
+{
+ ac97->id = ac97->bus->ops->read(ac97, AC97_VENDOR_ID1) << 16;
+ ac97->id |= ac97->bus->ops->read(ac97, AC97_VENDOR_ID2);
+
+ if (ac97->id == 0x0 || ac97->id == 0xffffffff)
+ return false;
+
+ if (id != 0 && id != (ac97->id & id_mask))
+ return false;
+
+ return true;
+}
+
+/**
+ * snd_ac97_reset() - Reset AC'97 device
+ * @ac97: The AC'97 device to reset
+ * @try_warm: Try a warm reset first
+ * @id: Expected device vendor ID
+ * @id_mask: Mask that is applied to the device ID before comparing to @id
+ *
+ * This function resets the AC'97 device. If @try_warm is true the function
+ * first performs a warm reset. If the warm reset is successful the function
+ * returns 1. Otherwise or if @try_warm is false the function issues cold reset
+ * followed by a warm reset. If this is successful the function returns 0,
+ * otherwise a negative error code. If @id is 0 any valid device ID will be
+ * accepted, otherwise only the ID that matches @id and @id_mask is accepted.
+ */
+int snd_ac97_reset(struct snd_ac97 *ac97, bool try_warm, unsigned int id,
+ unsigned int id_mask)
+{
+ struct snd_ac97_bus_ops *ops = ac97->bus->ops;
+
+ if (try_warm && ops->warm_reset) {
+ ops->warm_reset(ac97);
+ if (snd_ac97_check_id(ac97, id, id_mask))
+ return 1;
+ }
+
+ if (ops->reset)
+ ops->reset(ac97);
+ if (ops->warm_reset)
+ ops->warm_reset(ac97);
+
+ if (snd_ac97_check_id(ac97, id, id_mask))
+ return 0;
+
+ return -ENODEV;
+}
+EXPORT_SYMBOL_GPL(snd_ac97_reset);
+
+/*
+ * Let drivers decide whether they want to support given codec from their
+ * probe method. Drivers have direct access to the struct snd_ac97
+ * structure and may decide based on the id field amongst other things.
+ */
+static int ac97_bus_match(struct device *dev, struct device_driver *drv)
+{
+ return 1;
+}
+
+struct bus_type ac97_bus_type = {
+ .name = "ac97",
+ .match = ac97_bus_match,
+};
+
+static int __init ac97_bus_init(void)
+{
+ return bus_register(&ac97_bus_type);
+}
+
+subsys_initcall(ac97_bus_init);
+
+static void __exit ac97_bus_exit(void)
+{
+ bus_unregister(&ac97_bus_type);
+}
+
+module_exit(ac97_bus_exit);
+
+EXPORT_SYMBOL(ac97_bus_type);
+
+MODULE_LICENSE("GPL");