[PATCH v3] 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.

Fixes: c6267a51639b ("usb: dwc3: gadget: align transfers to wMaxPacketSize")
Cc: sta...@vger.kernel.org

Signed-off-by: Tejas Joglekar <jogle...@synopsys.com>
---
Changes in v3:
 - Enclose summary for fixes with " " and no wrap

Changes in v2:
 - Remove sg patch hunk
 - Added fixes and stable tag

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

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index bed2ff4..6c9b76b 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -1119,7 +1119,7 @@ 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