[PATCH] ref-manual/variables.rst: document the QB_DEFAULT_BIOS variable

[Antonin Godard <antonin.godard@bootlin.com>]

The QB_DEFAULT_BIOS allows setting the -bios parameter of QEMU, which
can be used to emulate U-Boot, for example.

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
---
 documentation/ref-manual/variables.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
index e75f42afe..cfc764961 100644
--- a/documentation/ref-manual/variables.rst
+++ b/documentation/ref-manual/variables.rst
@@ -8084,6 +8084,18 @@ system and gives an overview of their function and contents.
       replaces the ``@CLIENT@`` and ``@GATEWAY@`` place holders by the IP and
       the gateway address of the QEMU guest.
 
+   :term:`QB_DEFAULT_BIOS`
+      the `QB_DEFAULT_BIOS` variable can be used to add the ``-bios`` option to
+      the initialization parameters of QEMU. For example, this parameter can be
+      set as follows to emulate U-Boot for the :oecore_path:`qemuarm64
+      <meta/conf/machine/qemuarm64.conf>` machine::
+
+         QB_DEFAULT_BIOS = "u-boot.bin"
+
+      The above example makes the assumption you have built the U-Boot recipe
+      and that the ``u-boot.bin`` file is located in the
+      :term:`DEPLOY_DIR_IMAGE` directory.
+
    :term:`QB_DEFAULT_FSTYPE`
 
       The :term:`QB_DEFAULT_FSTYPE` variable controls the default filesystem

---
base-commit: 41dae3c3da3ada1745fc60228ff6269c64ee2361
change-id: 20260804-qb-default-bios-7c12e88f0db2