RE: Fw: [PATCH]: Correctly locate RSDP in EBDA

There are two versions of this code in Linux, the ACPICA version and the
version in boot.c. It is very cumbersome to maintain two versions of
this sensitive code, and the version in boot.c should be removed.  The
ACPICA version (in tbxfroot.c) already handles EBDA and bad checksums
correctly.

Bob Moore

-----Original Message-----
From: acpi-devel-admin-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org [mailto:acpi-devel-
admin-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org] On Behalf Of Andrew Morton
Sent: Monday, July 25, 2005 3:13 PM
To: acpi-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Cc: Udo A. Steinberg
Subject: [ACPI] Fw: [PATCH]: Correctly locate RSDP in EBDA



Begin forwarded message:

Date: Wed, 20 Jul 2005 17:42:07 +0200
From: "Udo A. Steinberg" <us15-IG//nw+yl+iQIjdd1DhZXWfrygkm6VTR@public.gmane.org>
To: Linux Kernel Mailing List <redacted>
Subject: [PATCH]: Correctly locate RSDP in EBDA



ACPI spec. states that the location of the RSDP structure is found by
searching
* The first 1 KB of the Extended BIOS Data Area (EBDA).
* The BIOS read-only memory space between 0E0000h and 0FFFFFh

The EBDA scan looks wrong. The patch below against 2.6.12 should

correct

this.

-Udo.

---

Calculate correct EBDA address for ACPI RSDP scan. The word at BIOS

Data

quoted hunk

Area
40:0E is the segment address of the EBDA.

Signed-off-by: Udo A. Steinberg <us15-IG//nw+yl+iQIjdd1DhZXWfrygkm6VTR@public.gmane.org>

--- linux-2.6.12/arch/i386/kernel/acpi/boot.c.old       2005-07-20

17:28:32.000000000 +0200

+++ linux-2.6.12/arch/i386/kernel/acpi/boot.c   2005-07-20

17:31:15.000000000 +0200

@@ -648,7 +648,7 @@
         * Scan memory looking for the RSDP signature. First search

EBDA

(low
         * memory) paragraphs and then search upper memory

(E0000-FFFFF).

quoted hunk

         */
-       rsdp_phys = acpi_scan_rsdp (0, 0x400);
+       rsdp_phys = acpi_scan_rsdp (*(u16*) 0x40E << 4, 0x400);
        if (!rsdp_phys)
                rsdp_phys = acpi_scan_rsdp (0xE0000, 0x20000);

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