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+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/firmware/qemu,fw-cfg-mmio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: QEMU Firmware Configuration bindings
+
+maintainers:
+ - Rob Herring <robh@kernel.org>
+
+description: |
+ Various QEMU emulation / virtualization targets provide the following
+ Firmware Configuration interface on the "virt" machine type:
+
+ - A write-only, 16-bit wide selector (or control) register,
+ - a read-write, 64-bit wide data register.
+
+ QEMU exposes the control and data register to guests as memory mapped
+ registers; their location is communicated to the guest's UEFI firmware in the
+ DTB that QEMU places at the bottom of the guest's DRAM.
+
+ The authoritative guest-side hardware interface documentation to the fw_cfg
+ device can be found in "docs/specs/fw_cfg.txt" in the QEMU source tree.
+
+
+properties:
+ compatible:
+ const: qemu,fw-cfg-mmio
+
+ reg:
+ maxItems: 1
+ description: |
+ * Bytes 0x0 to 0x7 cover the data register.
+ * Bytes 0x8 to 0x9 cover the selector register.
+ * Further registers may be appended to the region in case of future interface
+ revisions / feature bits.
+
+ dma-coherent: true
+
+required:
+ - compatible
+ - reg
+
+additionalProperties: false
+
+examples:
+ - |
+
+ fw-cfg@9020000 {
+ compatible = "qemu,fw-cfg-mmio";
+ reg = <0x9020000 0xa>;
+ };
+...