[PATCH] usb: dwc2: Add small delay after reset

[Ley Foon Tan]

In Cyclone 5 SoC platform, the first USB probing is failed but second
probing is success. DWC2 driver read gsnpsid register right after de-assert
reset, but controller is not ready yet and it returns gsnpsid 0.
Adding small delay after de-assert reset solve the issue.

Retry with this fix more than 10 times without issue.

=> usb reset
resetting USB...
Bus usb at ffb40000: usb probe
SNPSID invalid (not DWC2 OTG device): 00000000
Port not available.
=> usb reset
resetting USB...
Bus usb at ffb40000: usb probe
scanning bus usb at ffb40000 for devices... 2 USB Device(s) found
       scanning usb for storage devices... 1 Storage Device(s) found

Signed-off-by: Ley Foon Tan <ley.foon.tan at intel.com>
---
 drivers/usb/host/dwc2.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/usb/host/dwc2.c b/drivers/usb/host/dwc2.c
index b9c56f763b..cbbef19201 100644
--- a/drivers/usb/host/dwc2.c
+++ b/drivers/usb/host/dwc2.c
@@ -1153,6 +1153,11 @@ static int dwc2_reset(struct udevice *dev)
 		return ret;
 	}
 
+	/* Certain controller takes some time to complete the reset,
+	 * add small delay before access it.
+	 */
+	udelay(5);
+
 	return 0;
 }
 
-- 
2.19.0