[QEMU HCI-8.0 PATCH v2 12/13] hcd-xhci: resync isochronous endpoints after CPR #VSTOR-137800

[Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>]

An isochronous endpoint has no retransmission, so the transfer events
the controller reports have to line up with the TDs the guest driver is
sitting on.  Across CPR we rebuild the controller's transient transfer
and scheduling state out of guest memory, and it no longer matches what
the guest has already consumed - so the very first event after resume
lands on the wrong TD and the guest wedges with "not part of TD".

Let's report CC_MISSED_SERVICE_ERROR on the first isochronous transfer
after a CPR resume, just like a real xHCI does when it misses a service
interval.  That arms the guest driver's skip logic, and it resyncs to
the live stream instead of getting stuck.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 hw/usb/hcd-xhci.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
index 292c378bfc9..b02e5b4b67f 100644
--- a/hw/usb/hcd-xhci.c
+++ b/hw/usb/hcd-xhci.c
@@ -282,6 +282,7 @@ struct XHCIEPContext {
     unsigned int max_psize;
     uint32_t state;
     uint32_t kick_active;
+    bool cpr_iso_resync; /* resync iso stream on first kick after CPR resume */
 
     /* streams */
     unsigned int max_pstreams;
@@ -1811,6 +1812,19 @@ static int xhci_submit(XHCIState *xhci, XHCITransfer *xfer, XHCIEPContext *epctx
         xfer->pkts = 1;
         xfer->iso_xfer = true;
         xfer->timed_xfer = true;
+        if (epctx->cpr_iso_resync) {
+            /*
+             * First iso TD after a CPR resume: our transfer state was
+             * rebuilt from guest memory and no longer lines up with what
+             * the guest consumed.  Report a missed service, like real HW,
+             * to kick the driver's skip logic into resyncing.
+             */
+            epctx->cpr_iso_resync = false;
+            xfer->status = CC_MISSED_SERVICE_ERROR;
+            xhci_xfer_report(xfer);
+            xfer->complete = 1;
+            return 0;
+        }
         mfindex = xhci_mfindex_get(xhci);
         xhci_calc_iso_kick(xhci, xfer, epctx, mfindex);
         xhci_check_intr_iso_kick(xhci, xfer, epctx, mfindex);
@@ -3510,6 +3524,10 @@ static int usb_xhci_post_load(void *opaque, int version_id)
             xhci_init_epctx(epctx, pctx, ep_ctx);
             epctx->state = state;
             if (state == EP_RUNNING) {
+                if (epctx->type == ET_ISO_IN || epctx->type == ET_ISO_OUT) {
+                    /* only iso streams need resyncing; see xhci_submit() */
+                    epctx->cpr_iso_resync = true;
+                }
                 /* kick endpoint after vmload is finished */
                 timer_mod(epctx->kick_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL));
             }
-- 
2.47.1