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[PATCH v9 10/19] docs/system/devices/usb: Note the automatic hub change
- To: "berrange@xxxxxxxxxx" <berrange@xxxxxxxxxx>, "junjie.cao@xxxxxxxxx" <junjie.cao@xxxxxxxxx>, "kraxel@xxxxxxxxxx" <kraxel@xxxxxxxxxx>, "marcandre.lureau@xxxxxxxxxx" <marcandre.lureau@xxxxxxxxxx>, "clg@xxxxxxxx" <clg@xxxxxxxx>, "junjie.cao@xxxxxxxxx" <junjie.cao@xxxxxxxxx>, Pierrick Bouvier <pierrick.bouvier@xxxxxxxxxxxxxxxx>, Peter Maydell <peter.maydell@xxxxxxxxxx>, Kane Chen <kane_chen@xxxxxxxxxxxxxx>, Philippe Mathieu-Daudé <philmd@xxxxxxxxxxxxxxxx>, Tyrone Ting <kfting@xxxxxxxxxxx>, Hao Wu <wuhaotsh@xxxxxxxxxx>, Zhao Liu <zhao1.liu@xxxxxxxxx>, Richard Henderson <richard.henderson@xxxxxxxxxx>, Helge Deller <deller@xxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Anthony PERARD <anthony@xxxxxxxxxxxxxx>, "Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxx>, "open list:All patches CC here" <qemu-devel@xxxxxxxxxx>, "open list:ASPEED BMCs" <qemu-arm@xxxxxxxxxx>, "open list:X86 Xen CPUs" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jamin Lin <jamin_lin@xxxxxxxxxxxxxx>
- Date: Tue, 10 Nov 2026 07:28:33 +0000
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- Cc: Jamin Lin <jamin_lin@xxxxxxxxxxxxxx>, Troy Lee <troy_lee@xxxxxxxxxxxxxx>
- Delivery-date: Tue, 10 Nov 2026 07:28:47 +0000
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- Thread-topic: [PATCH v9 10/19] docs/system/devices/usb: Note the automatic hub change
The automatic hub is now off for a new machine type. Say how to get a
hub back: plug in a usb-hub, or turn auto-hub back on for the
controller.
TODO: The text says 12.0. That is right once the compat entries move
to hw_compat_11_2.
Suggested-by: Junjie Cao <junjie.cao@xxxxxxxxx>
Signed-off-by: Jamin Lin <jamin_lin@xxxxxxxxxxxxxx>
---
docs/system/devices/usb.rst | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/docs/system/devices/usb.rst b/docs/system/devices/usb.rst
index dc694d23c2..dc73c4048e 100644
--- a/docs/system/devices/usb.rst
+++ b/docs/system/devices/usb.rst
@@ -3,8 +3,21 @@ USB emulation
QEMU can emulate a PCI UHCI, OHCI, EHCI or XHCI USB controller. You can
plug virtual USB devices or real host USB devices (only works with
-certain host operating systems). QEMU will automatically create and
-connect virtual USB hubs as necessary to connect multiple USB devices.
+certain host operating systems).
+
+A machine type older than 12.0 plugs a virtual USB hub into the last
+free port, so that more devices fit. A newer one does not, and a
+device that finds no free port fails.
+
+There are two ways to get a hub back. One is to add a hub yourself.
+Put it on the command line before the other USB devices::
+
+ -device usb-hub
+
+The other is to turn the automatic hub back on. Use the name of your
+USB controller, for example::
+
+ -global piix3-usb-uhci.auto-hub=on
USB controllers
~~~~~~~~~~~~~~~
--
2.43.0
|
