I've been debugging an ACPI-disabled-at-boot failure on an Acer
Travelmate C104TCi (C100) with a Wistron BIOS.
[ 0.000000] DMI 2.3 present.
[ 0.000000] ACPI: RSDP 000EC2D0, 0014 (r0 Acer )
[ 0.000000] ACPI: 00000000, F000FF5A (r195 Zÿ F000FF57 Zÿ F000FEA5)
[ 27.751333] ACPI: Core revision 20070126
[ 27.751501] ACPI Exception (tbxface-0618): AE_NO_ACPI_TABLES, While
loading namespace from ACPI tables [20070126]
[ 27.751654] ACPI: Unable to load the System Description Tables
[ 27.783596] ACPI: Interpreter disabled.
There are several references to this problem around the net and a couple
of invasive kernel patches that don't address the cause.
I wrote a user-space application that scans memory using the method
described in the ACPI specifications. It reports:
$ sudo ./find-RSDP
find-RSDP version 0.1 © 2007 TJ
Licensed on the terms of GPL version 3
Finds ACPI Root System Descriptor Pointer (for supported BIOS's only).
0x00000000FFFFFFFF Memory size
0x00000000000EC2D0 "RSD PTR "
0x00000000000FE030 "RSD PTR " RSDT @ 0FFE0000 OEM: "Acer " sum: 0
0x0000000005FBFE10 "RSD PTR "
Unfortunately the kernel function
arch/i386/kernel/acpi/boot.c::acpi_scan_rsdp()
doesn't fully implement the ACPI specification - it simply looks for the
first "RSD PTR " signature but doesn't check it has found a valid table
by calculating the checksum.
Because this series of BIOSs happen to have multiple instances of "RSD
PTR " and an invalid instance appears first in memory, the kernel tries
to use an invalid pointer to the RSDT, leading to the problems.
I've prepared a simple patch that calculates the checksum and only
returns an RSDT pointer if the checksum == 0.
Regards,
TJ.
Ubuntu Kernel ACPI Team
== Results With Patch Applied ==
[ 0.000000] BIOS-e820: 000000000ffe0000 - 000000000ffe8000 (ACPI data)
[ 0.000000] BIOS-e820: 000000000ffe8000 - 0000000010000000 (ACPI NVS)
[ 0.000000] ACPI: RSDP signature @ 0xC00EC2D0 checksum 218
[ 0.000000] ACPI: RSDP signature @ 0xC00FE030 checksum 0
[ 0.000000] ACPI: RSDP 000FE030, 0014 (r0 Acer )
[ 0.000000] ACPI: RSDT 0FFE0000, 002C (r1 Acer TM100 1 MSFT 1)
[ 0.000000] ACPI: FACP 0FFE0054, 0074 (r1 Acer TM100 1 MSFT 1)
[ 0.000000] ACPI: DSDT 0FFE00CC, 3E26 (r1 Acer AN100 1000 MSFT 100000E)
[ 0.000000] ACPI: FACS 0FFE8000, 0040
[ 0.000000] ACPI: BOOT 0FFE002C, 0028 (r1 Acer TM100 1 MSFT 1)
[ 0.000000] ACPI: PM-Timer IO Port: 0xf008
[ 18.351112] ACPI: Core revision 20070126
[ 18.351387] ACPI: Looking for DSDT in initramfs... successfully read 13997 bytes from /DSDT.aml.
[ 18.351656] ACPI: Table DSDT replaced by host OS
[ 18.351784] ACPI: DSDT 00000000, 36AD (r1 Acer AN100 1000 INTL 20061109)
[ 18.355337] ACPI: setting ELCR to 0200 (from 0c00)
[ 18.407892] ACPI: bus type pci registered
[ 18.438953] ACPI: EC: Look up EC in DSDT
[ 18.445067] ACPI: EC: GPE=0x18, ports=0x66, 0x62
[ 18.451387] ACPI: Interpreter enabled
[ 18.451446] ACPI: (supports S0 S3 S4 S5)
[ 18.451694] ACPI: Using PIC for interrupt routing
[ 18.472224] ACPI: EC: GPE=0x18, ports=0x66, 0x62
[ 18.472379] ACPI: PCI Root Bridge [PCI0] (0000:00)
[ 18.473052] PCI quirk: region f000-f03f claimed by PIIX4 ACPI
[ 18.473388] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0._PRT]
[ 18.476877] ACPI: PCI Interrupt Link [PILA] (IRQs *10 15)
[ 18.477341] ACPI: PCI Interrupt Link [PILB] (IRQs *11 15)
[ 18.477796] ACPI: PCI Interrupt Link [PILD] (IRQs *10 15)
[ 18.478266] pnp: PnP ACPI init
[ 18.478338] ACPI: bus type pnp registered
[ 18.489473] pnp: PnP ACPI: found 10 devices
[ 18.489535] ACPI: ACPI bus type pnp unregistered
[ 18.489597] PnPBIOS: Disabled by ACPI PNP
[ 18.489773] PCI: Using ACPI for IRQ routing
[ 18.534358] ACPI: PCI Interrupt Link [PILA] enabled at IRQ 10
[ 18.534429] ACPI: PCI Interrupt 0000:00:03.0[A] -> Link [PILA] -> GSI 10 (level, low) -> IRQ 10
[ 18.534590] ACPI: PCI Interrupt 0000:00:03.1[A] -> Link [PILA] -> GSI 10 (level, low) -> IRQ 10
[ 20.334950] ACPI: PCI Interrupt Link [PILB] enabled at IRQ 11
[ 20.335025] ACPI: PCI Interrupt 0000:00:00.2[B] -> Link [PILB] -> GSI 11 (level, low) -> IRQ 11
[ 20.335180] ACPI: PCI interrupt for device 0000:00:00.2 disabled
[ 20.794419] ACPI: CPU0 (power states: C1[C1] C2[C2] C3[C3] C4[C3])
[ 20.807239] ACPI: Thermal Zone [THR1] (32 C)
[ 20.817398] ACPI: Thermal Zone [THR2] (30 C)
[ 22.067049] ACPI: PCI Interrupt Link [PILD] enabled at IRQ 10
[ 22.068169] ACPI: PCI Interrupt 0000:00:05.0[A] -> Link [PILD] -> GSI 10 (level, low) -> IRQ 10
[ 22.173209] ACPI: PCI Interrupt 0000:00:04.0[A] -> Link [PILD] -> GSI 10 (level, low) -> IRQ 10
[ 22.474602] ACPI: PCI Interrupt 0000:00:07.2[D] -> Link [PILD] -> GSI 10 (level, low) -> IRQ 10
[ 23.608000] ACPI: PCI Interrupt 0000:00:00.1[B] -> Link [PILB] -> GSI 11 (level, low) -> IRQ 11
== Patch ==
--- arch/i386/kernel/acpi/boot.c.orig 2007-09-25 02:17:12.000000000 +0100
+++ arch/i386/kernel/acpi/boot.c 2007-09-25 08:31:05.000000000 +0100
@@ -592,9 +592,25 @@
* RSDP signature.
*/
for (offset = 0; offset < length; offset += 16) {
- if (strncmp((char *)(phys_to_virt(start) + offset), "RSD PTR ", sig_len))
- continue;
- return (start + offset);
+ if (strncmp((char *)(phys_to_virt(start) + offset), "RSD PTR ", sig_len) == 0) {
+ /* 2007-09-24 TJ <linux@xxxxxxxxxxx>
+ * The ACPI specification states the first 20 bytes of the RSDP table
+ * must have a checksum of 0 (ACPI 1.0b RSDP table is 20 bytes long).
+ * The signature can appear in multiple memory locations so don't rely
+ * on it as the sole proof of a valid table.
+ * This fixes broken/disabled ACPI problems with Acer Travelmate C100
+ * (and others) where the first signature match is accepted without
+ * confirming the checksum.
+ */
+ unsigned int i;
+ unsigned char checksum;
+ unsigned char *table = (unsigned char *)(phys_to_virt(start) + offset);
+ for (checksum = 0, i = 0; i < 20; i++)
+ checksum += table[i];
+
+ printk(KERN_WARNING PREFIX "RSDP signature @ 0x%0.8lX checksum %d\n", table, checksum);
+ if (checksum == 0) return (start + offset);
+ }
}
return 0;
-
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