usb: ci_udc: terminate ep0 INs with a zlp when required

Sometimes, a zero-length packet is required at the end of an IN
transaction so that the host knows the device is done sending data.
Enhance ci_udc to send a zlp when necessary. See the comments for
more details.

Signed-off-by: Stephen Warren <swarren@nvidia.com>

diff --git a/drivers/usb/gadget/ci_udc.c b/drivers/usb/gadget/ci_udc.c
index 435a2720e96fe506d409e29b5e593c1ab3242ddb..b18bee43ad894ed886076ac126a23fa42a6761e5 100644 (file)
--- a/drivers/usb/gadget/ci_udc.c
+++ b/drivers/usb/gadget/ci_udc.c
@@ -369,18 +369,50 @@ static void ci_ep_submit_next_request(struct ci_ep *ci_ep)
        ci_req = list_first_entry(&ci_ep->queue, struct ci_req, queue);
        len = ci_req->req.length;
 
-       item->next = TERMINATE;
-       item->info = INFO_BYTES(len) | INFO_IOC | INFO_ACTIVE;
+       item->info = INFO_BYTES(len) | INFO_ACTIVE;
        item->page0 = (uint32_t)ci_req->hw_buf;
        item->page1 = ((uint32_t)ci_req->hw_buf & 0xfffff000) + 0x1000;
        item->page2 = ((uint32_t)ci_req->hw_buf & 0xfffff000) + 0x2000;
        item->page3 = ((uint32_t)ci_req->hw_buf & 0xfffff000) + 0x3000;
        item->page4 = ((uint32_t)ci_req->hw_buf & 0xfffff000) + 0x4000;
-       ci_flush_qtd(num);
 
        head->next = (unsigned) item;
        head->info = 0;
 
+       /*
+        * When sending the data for an IN transaction, the attached host
+        * knows that all data for the IN is sent when one of the following
+        * occurs:
+        * a) A zero-length packet is transmitted.
+        * b) A packet with length that isn't an exact multiple of the ep's
+        *    maxpacket is transmitted.
+        * c) Enough data is sent to exactly fill the host's maximum expected
+        *    IN transaction size.
+        *
+        * One of these conditions MUST apply at the end of an IN transaction,
+        * or the transaction will not be considered complete by the host. If
+        * none of (a)..(c) already applies, then we must force (a) to apply
+        * by explicitly sending an extra zero-length packet.
+        */
+       /*  IN    !a     !b                              !c */
+       if (in && len && !(len % ci_ep->ep.maxpacket) && ci_req->req.zero) {
+               /*
+                * Each endpoint has 2 items allocated, even though typically
+                * only 1 is used at a time since either an IN or an OUT but
+                * not both is queued. For an IN transaction, item currently
+                * points at the second of these items, so we know that we
+                * can use (item - 1) to transmit the extra zero-length packet
+                */
+               item->next = (unsigned)(item - 1);
+               item--;
+               item->info = INFO_ACTIVE;
+       }
+
+       item->next = TERMINATE;
+       item->info |= INFO_IOC;
+
+       ci_flush_qtd(num);
+
        DBG("ept%d %s queue len %x, req %p, buffer %p\n",
            num, in ? "in" : "out", len, ci_req, ci_req->hw_buf);
        ci_flush_qh(num);