[PATCH] usb: cdnsp: fix for Link TRB with TC

[Pawel Laszczak <pawell@xxxxxxxxxxx>]

Stop Endpoint command on LINK TRB with TC bit set to 1 causes that
internal cycle bit can have incorrect state after command complete.
In consequence empty transfer ring can be incorrectly detected
when EP is resumed.
NOP TRB before LINK TRB avoid such scenario. Stop Endpoint command
is then on NOP TRB and internal cycle bit is not changed and have
correct value.

Fixes: 3d82904559f4 ("usb: cdnsp: cdns3 Add main part of Cadence USBSSP DRD Driver")
cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Pawel Laszczak <pawell@xxxxxxxxxxx>
---
 drivers/usb/cdns3/cdnsp-gadget.h |  3 +++
 drivers/usb/cdns3/cdnsp-ring.c   | 28 ++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/drivers/usb/cdns3/cdnsp-gadget.h b/drivers/usb/cdns3/cdnsp-gadget.h
index e1b5801fdddf..9a5577a772af 100644
--- a/drivers/usb/cdns3/cdnsp-gadget.h
+++ b/drivers/usb/cdns3/cdnsp-gadget.h
@@ -811,6 +811,7 @@ struct cdnsp_stream_info {
  *        generate Missed Service Error Event.
  *        Set skip flag when receive a Missed Service Error Event and
  *        process the missed tds on the endpoint ring.
+ * @wa1_nop_trb: hold pointer to NOP trb.
  */
 struct cdnsp_ep {
 	struct usb_ep endpoint;
@@ -838,6 +839,8 @@ struct cdnsp_ep {
 #define EP_UNCONFIGURED		BIT(7)
 
 	bool skip;
+	union cdnsp_trb	 *wa1_nop_trb;
+
 };
 
 /**
diff --git a/drivers/usb/cdns3/cdnsp-ring.c b/drivers/usb/cdns3/cdnsp-ring.c
index 275a6a2fa671..75724e60653c 100644
--- a/drivers/usb/cdns3/cdnsp-ring.c
+++ b/drivers/usb/cdns3/cdnsp-ring.c
@@ -1904,6 +1904,23 @@ int cdnsp_queue_bulk_tx(struct cdnsp_device *pdev, struct cdnsp_request *preq)
 	if (ret)
 		return ret;
 
+	/*
+	 * workaround 1: STOP EP command on LINK TRB with TC bit set to 1
+	 * causes that internal cycle bit can have incorrect state after
+	 * command complete. In consequence empty transfer ring can be
+	 * incorrectly detected when EP is resumed.
+	 * NOP TRB before LINK TRB avoid such scenario. STOP EP command is
+	 * then on NOP TRB and internal cycle bit is not changed and have
+	 * correct value.
+	 */
+	if (pep->wa1_nop_trb) {
+		field = le32_to_cpu(pep->wa1_nop_trb->trans_event.flags);
+		field ^= TRB_CYCLE;
+
+		pep->wa1_nop_trb->trans_event.flags = cpu_to_le32(field);
+		pep->wa1_nop_trb = NULL;
+	}
+
 	/*
 	 * Don't give the first TRB to the hardware (by toggling the cycle bit)
 	 * until we've finished creating all the other TRBs. The ring's cycle
@@ -1999,6 +2016,17 @@ int cdnsp_queue_bulk_tx(struct cdnsp_device *pdev, struct cdnsp_request *preq)
 		send_addr = addr;
 	}
 
+	if (cdnsp_trb_is_link(ring->enqueue + 1)) {
+		field = TRB_TYPE(TRB_TR_NOOP) | TRB_IOC;
+		if (!ring->cycle_state)
+			field |= TRB_CYCLE;
+
+		pep->wa1_nop_trb = ring->enqueue;
+
+		cdnsp_queue_trb(pdev, ring, 0, 0x0, 0x0,
+				TRB_INTR_TARGET(0), field);
+	}
+
 	cdnsp_check_trb_math(preq, enqd_len);
 	ret = cdnsp_giveback_first_trb(pdev, pep, preq->request.stream_id,
 				       start_cycle, start_trb);
-- 
2.43.0