[PATCH] usb: dwc3: gadget: Handle 0 xfer length for OUT EP

[Tejas Joglekar]

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.

Signed-off-by: Tejas Joglekar <jogle...@synopsys.com>
---
 drivers/usb/dwc3/gadget.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index e2caf9e..f1089ec 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1069,7 +1069,8 @@ static void dwc3_prepare_one_trb_sg(struct dwc3_ep *dep,
                if (sg_is_last(s))
                        chain = false;
 
-               if (rem && usb_endpoint_dir_out(dep->endpoint.desc) && !chain) {
+               if ((!length || rem) && usb_endpoint_dir_out(dep->endpoint.desc)
+                   && !chain) {
                        struct dwc3     *dwc = dep->dwc;
                        struct dwc3_trb *trb;
 
@@ -1114,7 +1115,7 @@ static void dwc3_prepare_one_trb_linear(struct dwc3_ep 
*dep,
        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;
 
-- 
2.7.4