Bluetooth: ath3k: workaround the compatibility issue with xHCI controller

BugLink: https://bugs.launchpad.net/bugs/1400215

ath3k devices fail to load firmwares on xHCI buses, but work well on
EHCI, this might be a compatibility issue between xHCI and ath3k chips.
As my testing result, those chips will work on xHCI buses again with
this patch.

This workaround is from Qualcomm, they also did some workarounds in
Windows driver.
Signed-off-by: NAdam Lee <adam.lee@canonical.com>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/ath3k.c

@@ -176,6 +176,8 @@ static const struct usb_device_id ath3k_blist_tbl[] = {
 #define USB_REQ_DFU_DNLOAD	1
 #define BULK_SIZE		4096
 #define FW_HDR_SIZE		20
+#define TIMEGAP_USEC_MIN	50
+#define TIMEGAP_USEC_MAX	100
 
 static int ath3k_load_firmware(struct usb_device *udev,
 				const struct firmware *firmware)
@@ -207,6 +209,9 @@ static int ath3k_load_firmware(struct usb_device *udev,
 	pipe = usb_sndbulkpipe(udev, 0x02);
 
 	while (count) {
+		/* workaround the compatibility issue with xHCI controller*/
+		usleep_range(TIMEGAP_USEC_MIN, TIMEGAP_USEC_MAX);
+
 		size = min_t(uint, count, BULK_SIZE);
 		memcpy(send_buf, firmware->data + sent, size);
 
@@ -304,6 +309,9 @@ static int ath3k_load_fwfile(struct usb_device *udev,
 	pipe = usb_sndbulkpipe(udev, 0x02);
 
 	while (count) {
+		/* workaround the compatibility issue with xHCI controller*/
+		usleep_range(TIMEGAP_USEC_MIN, TIMEGAP_USEC_MAX);
+
 		size = min_t(uint, count, BULK_SIZE);
 		memcpy(send_buf, firmware->data + sent, size);