path: root/dts/Bindings/arm/fw-cfg.txt
diff options
authorSascha Hauer <>2016-06-13 07:29:57 +0200
committerSascha Hauer <>2016-06-13 07:29:57 +0200
commita4f4bc65b33164eb8c19bcff9834cc87bcc845bb (patch)
treeef97762be5b614f160e9affddd1bbbec43c007dc /dts/Bindings/arm/fw-cfg.txt
parent83e61900b02965d01f0885e2db2077df35be7f56 (diff)
dts: update to v4.6-rc1
Signed-off-by: Sascha Hauer <>
Diffstat (limited to 'dts/Bindings/arm/fw-cfg.txt')
1 files changed, 2 insertions, 36 deletions
diff --git a/dts/Bindings/arm/fw-cfg.txt b/dts/Bindings/arm/fw-cfg.txt
index 953fb640d9..fd54e1db21 100644
--- a/dts/Bindings/arm/fw-cfg.txt
+++ b/dts/Bindings/arm/fw-cfg.txt
@@ -11,43 +11,9 @@ QEMU exposes the control and data register to ARM 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 guest writes a selector value (a key) to the selector register, and then
-can read the corresponding data (produced by QEMU) via the data register. If
-the selected entry is writable, the guest can rewrite it through the data
+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.
-The selector register takes keys in big endian byte order.
-The data register allows accesses with 8, 16, 32 and 64-bit width (only at
-offset 0 of the register). Accesses larger than a byte are interpreted as
-arrays, bundled together only for better performance. The bytes constituting
-such a word, in increasing address order, correspond to the bytes that would
-have been transferred by byte-wide accesses in chronological order.
-The interface allows guest firmware to download various parameters and blobs
-that affect how the firmware works and what tables it installs for the guest
-OS. For example, boot order of devices, ACPI tables, SMBIOS tables, kernel and
-initrd images for direct kernel booting, virtual machine UUID, SMP information,
-virtual NUMA topology, and so on.
-The authoritative registry of the valid selector values and their meanings is
-the QEMU source code; the structure of the data blobs corresponding to the
-individual key values is also defined in the QEMU source code.
-The presence of the registers can be verified by selecting the "signature" blob
-with key 0x0000, and reading four bytes from the data register. The returned
-signature is "QEMU".
-The outermost protocol (involving the write / read sequences of the control and
-data registers) is expected to be versioned, and/or described by feature bits.
-The interface revision / feature bitmap can be retrieved with key 0x0001. The
-blob to be read from the data register has size 4, and it is to be interpreted
-as a uint32_t value in little endian byte order. The current value
-(corresponding to the above outer protocol) is zero.
-The guest kernel is not expected to use these registers (although it is
-certainly allowed to); the device tree bindings are documented here because
-this is where device tree bindings reside in general.
Required properties: