[PATCH 4.19 294/313] usb: dwc3: gadget: Handle 0 xfer length for OUT EP

[Greg Kroah-Hartman]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tejas Joglekar <tejas.joglekar@xxxxxxxxxxxx>

commit 1e19cdc8060227b0802bda6bc0bd22b23679ba32 upstream.

For OUT endpoints, zero-length transfers require MaxPacketSize buffer as
per the DWC_usb3 programming guide 3.30a section 4.2.3.3.

This patch fixes this by explicitly checking zero length
transfer to correctly pad up to MaxPacketSize.

Fixes: c6267a51639b ("usb: dwc3: gadget: align transfers to wMaxPacketSize")
Cc: stable@xxxxxxxxxxxxxxx

Signed-off-by: Tejas Joglekar <joglekar@xxxxxxxxxxxx>
Signed-off-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/usb/dwc3/gadget.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1110,7 +1110,7 @@ static void dwc3_prepare_one_trb_linear(
 	unsigned int maxp = usb_endpoint_maxp(dep->endpoint.desc);
 	unsigned int rem = length % maxp;
 
-	if (rem && usb_endpoint_dir_out(dep->endpoint.desc)) {
+	if ((!length || rem) && usb_endpoint_dir_out(dep->endpoint.desc)) {
 		struct dwc3	*dwc = dep->dwc;
 		struct dwc3_trb	*trb;