v4.19.13 snapshot.
diff --git a/sound/usb/helper.c b/sound/usb/helper.c
new file mode 100644
index 0000000..7712e2b
--- /dev/null
+++ b/sound/usb/helper.c
@@ -0,0 +1,133 @@
+/*
+ * 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.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *
+ */
+
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/usb.h>
+
+#include "usbaudio.h"
+#include "helper.h"
+#include "quirks.h"
+
+/*
+ * combine bytes and get an integer value
+ */
+unsigned int snd_usb_combine_bytes(unsigned char *bytes, int size)
+{
+ switch (size) {
+ case 1: return *bytes;
+ case 2: return combine_word(bytes);
+ case 3: return combine_triple(bytes);
+ case 4: return combine_quad(bytes);
+ default: return 0;
+ }
+}
+
+/*
+ * parse descriptor buffer and return the pointer starting the given
+ * descriptor type.
+ */
+void *snd_usb_find_desc(void *descstart, int desclen, void *after, u8 dtype)
+{
+ u8 *p, *end, *next;
+
+ p = descstart;
+ end = p + desclen;
+ for (; p < end;) {
+ if (p[0] < 2)
+ return NULL;
+ next = p + p[0];
+ if (next > end)
+ return NULL;
+ if (p[1] == dtype && (!after || (void *)p > after)) {
+ return p;
+ }
+ p = next;
+ }
+ return NULL;
+}
+
+/*
+ * find a class-specified interface descriptor with the given subtype.
+ */
+void *snd_usb_find_csint_desc(void *buffer, int buflen, void *after, u8 dsubtype)
+{
+ unsigned char *p = after;
+
+ while ((p = snd_usb_find_desc(buffer, buflen, p,
+ USB_DT_CS_INTERFACE)) != NULL) {
+ if (p[0] >= 3 && p[2] == dsubtype)
+ return p;
+ }
+ return NULL;
+}
+
+/*
+ * Wrapper for usb_control_msg().
+ * Allocates a temp buffer to prevent dmaing from/to the stack.
+ */
+int snd_usb_ctl_msg(struct usb_device *dev, unsigned int pipe, __u8 request,
+ __u8 requesttype, __u16 value, __u16 index, void *data,
+ __u16 size)
+{
+ int err;
+ void *buf = NULL;
+ int timeout;
+
+ if (size > 0) {
+ buf = kmemdup(data, size, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+ }
+
+ if (requesttype & USB_DIR_IN)
+ timeout = USB_CTRL_GET_TIMEOUT;
+ else
+ timeout = USB_CTRL_SET_TIMEOUT;
+
+ err = usb_control_msg(dev, pipe, request, requesttype,
+ value, index, buf, size, timeout);
+
+ if (size > 0) {
+ memcpy(data, buf, size);
+ kfree(buf);
+ }
+
+ snd_usb_ctl_msg_quirk(dev, pipe, request, requesttype,
+ value, index, data, size);
+
+ return err;
+}
+
+unsigned char snd_usb_parse_datainterval(struct snd_usb_audio *chip,
+ struct usb_host_interface *alts)
+{
+ switch (snd_usb_get_speed(chip->dev)) {
+ case USB_SPEED_HIGH:
+ case USB_SPEED_WIRELESS:
+ case USB_SPEED_SUPER:
+ case USB_SPEED_SUPER_PLUS:
+ if (get_endpoint(alts, 0)->bInterval >= 1 &&
+ get_endpoint(alts, 0)->bInterval <= 4)
+ return get_endpoint(alts, 0)->bInterval - 1;
+ break;
+ default:
+ break;
+ }
+ return 0;
+}
+