[PULL,5/6] fw_cfg: document ACPI device node information
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Message ID 1457435941-17578-6-git-send-email-kraxel@redhat.com
State New
Headers show

Commit Message

Gerd Hoffmann March 8, 2016, 11:19 a.m. UTC
From: "Gabriel L. Somlo" <somlo@cmu.edu>

Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Marc MarĂ­ <markmb@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-id: 1455906029-25565-6-git-send-email-somlo@cmu.edu
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
 docs/specs/fw_cfg.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

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diff --git a/docs/specs/fw_cfg.txt b/docs/specs/fw_cfg.txt
index 2099ad9..5414140 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) ===