[PATCH v2 1/1] docs: pcie: describe PCIe option ROMs

[Heinrich Schuchardt <heinrich.schuchardt@canonical.com>]

Provide a descriptions of the options that control the emulation of option
ROMS for PCIe devices.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
---
v2:
	correct description of rombar property
	use romfile= to suppress option ROM loading
---
 docs/pcie.txt | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/docs/pcie.txt b/docs/pcie.txt
index 89e3502075..b60f189bd4 100644
--- a/docs/pcie.txt
+++ b/docs/pcie.txt
@@ -292,6 +292,34 @@ PCI-PCI Bridge slots can be used for legacy PCI host devices.
 If you can see the "Express Endpoint" capability in the
 output, then the device is indeed PCI Express.
 
+8. Option ROM
+=============
+PCIe devices may provide an option ROM. The following properties control the
+emulation of the option ROM:
+
+``rombar`` (default: ``1``)
+  For vfio-pci devices a vendor and product ID based denylist exists which
+  controls if an available option ROM shall be probed. The 'rombar' option
+  allows to override this setting. The value is used as follows:
+  0 = skip probing, 1 = force probing
+
+``romfile``
+  Defines the name of the file to be loaded as option ROM.
+  The file size may neither exceed 2 GiB nor ``romsize``.
+  Some devices like virtio-net-pci define a default file name.
+
+``romsize`` (default: ``-1``)
+  Specifies the size of the option ROM in bytes. The value must be either
+  ``-1`` or a power of two. ``-1`` signifies unlimited size.
+
+Some QEMU PCIe devices like virtio-net-pci use an option ROM by default. In the
+following example the option ROM of a virtio-net-pci device is disabled by
+specifying an empty ``romfile`` property. This is useful for architectures where
+QEMU does not supply an option ROM file.
+
+.. code-block:: console
+
+    -device virtio-net-pci,netdev=eth1,mq=on,romfile=
 
 7. Virtio devices
 =================
-- 
2.36.1