Hello,
Subject could be :
docs: add mdpy mdev vfio display testing guide ?
On 6/11/26 11:03, Marc-André Lureau wrote:
Add a section to help me remember how to test vfio display hotplug.
May be :
Document how to test VFIO display hotplug using the kernel mdpy mdev
sample
Signed-off-by: Marc-André Lureau <[email protected]>
---
docs/devel/index-internals.rst | 1 +
docs/devel/vfio-mdpy.rst | 83 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 84 insertions(+)
diff --git a/docs/devel/index-internals.rst b/docs/devel/index-internals.rst
index 7a0678cbdd3..198f155247a 100644
--- a/docs/devel/index-internals.rst
+++ b/docs/devel/index-internals.rst
@@ -22,6 +22,7 @@ Details about QEMU's various subsystems including how to add
features to them.
tracing
uefi-vars
vfio-iommufd
+ vfio-mdpy
writing-monitor-commands
virtio-backends
crypto
diff --git a/docs/devel/vfio-mdpy.rst b/docs/devel/vfio-mdpy.rst
new file mode 100644
index 00000000000..14cddd11d81
--- /dev/null
+++ b/docs/devel/vfio-mdpy.rst
@@ -0,0 +1,83 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+===================================
+Testing VFIO display with mdev mdpy
+===================================
+
+.. contents:: Table of Contents
+
+The kernel provides a sample mediated device driver, ``mdpy``
+(``samples/vfio-mdev/mdpy.c``), that exposes a fake framebuffer through the
VFIO
+display region interface. It can be used to test VFIO display support,
including
+hotplug, without any real GPU hardware.
+
+The kernel modules
+==================
+
+The ``mdpy`` driver depends on the ``mdev`` subsystem. Enable, build and load
+the modules.
The minimal set is:
CONFIG_SAMPLE_VFIO_MDEV_MDPY=m
CONFIG_SAMPLE_VFIO_MDEV_MDPY_FB=m # guest framebuffer driver
CONFIG_VFIO_MDEV is selected automatically.
+
+Verify that the driver registered successfully:
+
+.. code-block:: bash
+
+ ls /sys/devices/virtual/mdpy/mdpy/mdev_supported_types/
+
+Creating an mdev instance
+=========================
+
+Available types correspond to different resolutions (e.g. ``mdpy-vga``
+for 640x480, ``mdpy-xga`` for 1024x768, ``mdpy-hd`` for 1920x1080).
+
+Each mdev instance is identified by a UUID:
+
+.. code-block:: bash
+
+ uuid=$(uuidgen)
+ echo "$uuid" >
/sys/devices/virtual/mdpy/mdpy/mdev_supported_types/mdpy-xga/create
+
+To remove the instance later:
+
+.. code-block:: bash
+
+ echo 1 > /sys/bus/mdev/devices/$uuid/remove
+
+Make sure your user has the necessary permissions to access the vfio group.
+(ex: chmod 666 /dev/vfio/16)
+
+Starting QEMU
+=============
+
+Boot-time attachment
+--------------------
+
+.. code-block:: bash
+
+ qemu-system-x86_64 -machine q35 -m 1G \
+ -device vfio-pci,sysfsdev=/sys/bus/mdev/devices/$uuid,display=on \
+ -display gtk,gl=on
+
+Hotplug via HMP
+---------------
+
+Start QEMU with a PCIe root port (required for PCIe hotplug) and a
+monitor:
+
+.. code-block:: bash
+
+ qemu-system-x86_64 -machine q35 -m 1G \
+ -device pcie-root-port,id=rp0,slot=1 \
+ -display gtk,gl=on \
+ -monitor stdio
+
+Then at the ``(qemu)`` prompt:
+
+.. code-block:: none
+
+ device_add
vfio-pci,sysfsdev=/sys/bus/mdev/devices/<uuid>,display=on,bus=rp0,id=mdpy0
+
+To hot-unplug:
+
+.. code-block:: none
+
+ device_del mdpy0
Thanks,
C.
