[PATCH v2] usb: dwc3: gadget: Fix .udc_set_speed()

[Roger Quadros]

Currently UDC core calls ->udc_set_speed() with the speed parameter
containing the maximum speed supported by the gadget function
driver. This might very well be more than that supported by the
UDC controller driver.

Select the lesser of the 2 speeds so both UDC and gadget function
driver are operating within limits.

This fixes PHY Erratic errors and 2 second enumeration delay on
TI's AM437x platforms.

Fixes: 6099eca796ae ("usb: gadget: core: introduce ->udc_set_speed() method")
Cc: <stable@xxxxxxxxxxxxxxx> # v4.13+
Reported-by: Dylan Howey <Dylan.Howey@xxxxxxxxxxxxx>
Signed-off-by: Roger Quadros <rogerq@xxxxxx>
---
v2:
- Move speed limiting code to UDC core.

 drivers/usb/gadget/udc/core.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
index d41d07a..def1b05 100644
--- a/drivers/usb/gadget/udc/core.c
+++ b/drivers/usb/gadget/udc/core.c
@@ -1080,8 +1080,12 @@ static inline void usb_gadget_udc_stop(struct usb_udc *udc)
 static inline void usb_gadget_udc_set_speed(struct usb_udc *udc,
 					    enum usb_device_speed speed)
 {
-	if (udc->gadget->ops->udc_set_speed)
-		udc->gadget->ops->udc_set_speed(udc->gadget, speed);
+	if (udc->gadget->ops->udc_set_speed) {
+		enum usb_device_speed s;
+
+		s = min(speed, udc->gadget->max_speed);
+		udc->gadget->ops->udc_set_speed(udc->gadget, s);
+	}
 }
 
 /**
-- 
cheers,
-roger

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