Implement TR NOOP commands by setting up then immediately completing
the packet. Add a TR NOOP test to the xhci qtest.

The IBM AIX XHCI driver uses NOOP commands to check driver and
hardware health.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 hw/usb/hcd-xhci.c               | 28 ++++++++++++++++++++++++++-
 tests/qtest/usb-hcd-xhci-test.c | 34 +++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
index d85adaca0d..9e223acd83 100644
--- a/hw/usb/hcd-xhci.c
+++ b/hw/usb/hcd-xhci.c
@@ -1832,6 +1832,20 @@ static int xhci_fire_transfer(XHCIState *xhci, XHCITransfer *xfer, XHCIEPContext
     return xhci_submit(xhci, xfer, epctx);
 }
 
+static int xhci_noop_transfer(XHCIState *xhci, XHCITransfer *xfer)
+{
+    /*
+     * TR NOOP conceptually probably better not call into USB subsystem
+     * (usb_packet_setup() via xhci_setup_packet()). In practice it
+     * works and avoids code duplication.
+     */
+    if (xhci_setup_packet(xfer) < 0) {
+        return -1;
+    }
+    xhci_try_complete_packet(xfer);
+    return 0;
+}
+
 static void xhci_kick_ep(XHCIState *xhci, unsigned int slotid,
                          unsigned int epid, unsigned int streamid)
 {
@@ -1954,6 +1968,8 @@ static void xhci_kick_epctx(XHCIEPContext *epctx, unsigned int streamid)
 
     epctx->kick_active++;
     while (1) {
+        bool noop = false;
+
         length = xhci_ring_chain_length(xhci, ring);
         if (length <= 0) {
             if (epctx->type == ET_ISO_OUT || epctx->type == ET_ISO_IN) {
@@ -1982,10 +1998,20 @@ static void xhci_kick_epctx(XHCIEPContext *epctx, unsigned int streamid)
                 epctx->kick_active--;
                 return;
             }
+            if (type == TR_NOOP) {
+                noop = true;
+            }
         }
         xfer->streamid = streamid;
 
-        if (epctx->epid == 1) {
+        if (noop) {
+            if (length != 1) {
+                qemu_log_mask(LOG_GUEST_ERROR,
+                              "%s: NOOP TR TRB within TRB chain!\n", __func__);
+                /* Undefined behavior, we no-op the entire chain */
+            }
+            xhci_noop_transfer(xhci, xfer);
+        } else if (epctx->epid == 1) {
             xhci_fire_ctl_transfer(xhci, xfer);
         } else {
             xhci_fire_transfer(xhci, xfer, epctx);
diff --git a/tests/qtest/usb-hcd-xhci-test.c b/tests/qtest/usb-hcd-xhci-test.c
index d66e76f070..8a36f42522 100644
--- a/tests/qtest/usb-hcd-xhci-test.c
+++ b/tests/qtest/usb-hcd-xhci-test.c
@@ -357,6 +357,30 @@ static void submit_cr_trb(XHCIQState *s, XHCITRB *trb)
     xhci_db_writel(s, 0, 0); /* doorbell 0 */
 }
 
+static void submit_tr_trb(XHCIQState *s, int slot, XHCITRB *trb)
+{
+    XHCITRB t;
+    uint64_t tr_addr = s->slots[slot].transfer_ring + s->slots[slot].tr_trb_idx * sizeof(*trb);
+
+    trb->control |= s->slots[slot].tr_trb_c; /* C */
+
+    t.parameter = cpu_to_le64(trb->parameter);
+    t.status = cpu_to_le32(trb->status);
+    t.control = cpu_to_le32(trb->control);
+
+    qtest_memwrite(s->parent->qts, tr_addr, &t, sizeof(t));
+    s->slots[slot].tr_trb_idx++;
+    /* Last entry contains the link, so wrap back */
+    if (s->slots[slot].tr_trb_idx == s->slots[slot].tr_trb_entries - 1) {
+        set_link_trb(s, s->slots[slot].transfer_ring,
+                        s->slots[slot].tr_trb_c,
+                        s->slots[slot].tr_trb_entries);
+        s->slots[slot].tr_trb_idx = 0;
+        s->slots[slot].tr_trb_c ^= 1;
+    }
+    xhci_db_writel(s, slot, 1); /* doorbell slot, EP0 target */
+}
+
 static void pci_xhci_stress_rings(void)
 {
     XHCIQState *s;
@@ -509,6 +533,16 @@ static void pci_xhci_stress_rings(void)
 
     /* XXX: Check EP state is running? */
 
+    /* Wrap the transfer ring a few times */
+    for (i = 0; i < 100; i++) {
+        /* Issue a transfer ring slot 0 noop */
+        memset(&trb, 0, sizeof(trb));
+        trb.control |= TR_NOOP << TRB_TYPE_SHIFT;
+        trb.control |= TRB_TR_IOC;
+        submit_tr_trb(s, slotid, &trb);
+        wait_event_trb(s, &trb);
+    }
+
     /* Shut it down */
     qpci_msix_disable(s->dev);
 
-- 
2.45.2