Implement XHCI TR NOOP commands by setting up then immediately
completing the packet.

The IBM AIX XHCI HCD driver uses NOOP commands to check driver and
hardware health, which works after this change.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 hw/usb/hcd-xhci.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
index ef9f2a7db41..6a490a5febf 100644
--- a/hw/usb/hcd-xhci.c
+++ b/hw/usb/hcd-xhci.c
@@ -1664,6 +1664,20 @@ 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)
 {
@@ -1786,6 +1800,8 @@ 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) {
@@ -1814,10 +1830,20 @@ 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);
-- 
2.47.1

On Fri, 2 May 2025 at 04:33, Nicholas Piggin <npiggin@gmail.com> wrote:
>
> Implement XHCI TR NOOP commands by setting up then immediately
> completing the packet.
>
> The IBM AIX XHCI HCD driver uses NOOP commands to check driver and
> hardware health, which works after this change.
>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  hw/usb/hcd-xhci.c | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM