1* QEMU Firmware Configuration bindings for ARM 2 3QEMU's arm-softmmu and aarch64-softmmu emulation / virtualization targets 4provide the following Firmware Configuration interface on the "virt" machine 5type: 6 7- A write-only, 16-bit wide selector (or control) register, 8- a read-write, 64-bit wide data register. 9 10QEMU exposes the control and data register to ARM guests as memory mapped 11registers; their location is communicated to the guest's UEFI firmware in the 12DTB that QEMU places at the bottom of the guest's DRAM. 13 14The authoritative guest-side hardware interface documentation to the fw_cfg 15device can be found in "docs/specs/fw_cfg.txt" in the QEMU source tree. 16 17 18Required properties: 19 20- compatible: "qemu,fw-cfg-mmio". 21 22- reg: the MMIO region used by the device. 23 * Bytes 0x0 to 0x7 cover the data register. 24 * Bytes 0x8 to 0x9 cover the selector register. 25 * Further registers may be appended to the region in case of future interface 26 revisions / feature bits. 27 28Example: 29 30/ { 31 #size-cells = <0x2>; 32 #address-cells = <0x2>; 33 34 fw-cfg@9020000 { 35 compatible = "qemu,fw-cfg-mmio"; 36 reg = <0x0 0x9020000 0x0 0xa>; 37 }; 38}; 39