From 36a43ea83b4426344592523fd560e5f76c4867c4 Mon Sep 17 00:00:00 2001 From: "Gabriel L. Somlo" Date: Fri, 19 Feb 2016 13:20:29 -0500 Subject: fw_cfg: document ACPI device node information MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Signed-off-by: Gabriel Somlo Reviewed-by: Laszlo Ersek Reviewed-by: Marc Marí Reviewed-by: Michael S. Tsirkin Message-id: 1455906029-25565-6-git-send-email-somlo@cmu.edu Signed-off-by: Gerd Hoffmann --- docs/specs/fw_cfg.txt | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/docs/specs/fw_cfg.txt b/docs/specs/fw_cfg.txt index 2099ad9a4d..5414140f33 100644 --- a/docs/specs/fw_cfg.txt +++ b/docs/specs/fw_cfg.txt @@ -84,6 +84,15 @@ Selector Register address: Base + 8 (2 bytes) Data Register address: Base + 0 (8 bytes) DMA Address address: Base + 16 (8 bytes) +== ACPI Interface == + +The fw_cfg device is defined with ACPI ID "QEMU0002". Since we expect +ACPI tables to be passed into the guest through the fw_cfg device itself, +the guest-side firmware can not use ACPI to find fw_cfg. However, once the +firmware is finished setting up ACPI tables and hands control over to the +guest kernel, the latter can use the fw_cfg ACPI node for a more accurate +inventory of in-use IOport or MMIO regions. + == Firmware Configuration Items == === Signature (Key 0x0000, FW_CFG_SIGNATURE) === -- cgit v1.2.3