On 02/19/13 16:29, David Woodhouse wrote:
> On Mon, 2013-02-18 at 17:37 -0500, Kevin O'Connor wrote:
>> The ACPI v2 spec describes a "hard" reset register. SeaBIOS could
>> extract it from the FADT and then use it. Of course, we'd probably
>> want to update the QEMU ACPI tables to implement ACPI v2 then.
>
> This sounded great until I actually came to implement it.
>
> The PIIX reset at 0xcf9 requires *two* writes; one to set the reset type
> and then a second write with bit 2 set to actually do the reset.
>
> The ACPI RESET_REG definition only allows for *one* value to be written.
>
> Is that because the PIIX will actually do a hard reset when you write
> 0x06 to it *anyway*, despite theoretically saying that you should write
> 0x02 first? Or is the ACPI definition of RESET_REG simply incapable of
> being used on the PIIX?
The linux kernel actually considers BOOT_ACPI and BOOT_CF9 separate
things; see
- native_machine_emergency_restart() [arch/x86/kernel/reboot.c],
- acpi_reboot() [drivers/acpi/reboot.c],
- acpi_reset() [drivers/acpi/acpica/hwxface.c].
BOOT_ACPI looks like a single write in any case (io space, memory, pci
config).
Funnily enough, on my Thinkpad (
acpidump --table FACP --binary -o fadt.aml
iasl -d fadt.aml
):
/*
* Intel ACPI Component Architecture
* AML Disassembler version 20090123
*
* Disassembly of fadt.aml, Tue Feb 19 17:13:43 2013
*
* ACPI Data Table [FACP]
*
* Format: [HexOffset DecimalOffset ByteLength] FieldName : FieldValue
*/
[000h 000 4] Signature : "FACP" /* Fixed ACPI
Description Table */
[070h 112 4] Flags (decoded below) : 0000C2AD
Reset Register Supported (V2) : 0
[074h 116 12] Reset Register : <Generic Address Structure>
[074h 116 1] Space ID : 01 (SystemIO)
[075h 117 1] Bit Width : 08
[076h 118 1] Bit Offset : 00
[077h 119 1] Access Width : 00
[078h 120 8] Address : 0000000000000CF9
[080h 128 1] Value to cause reset : 06
Same on my HP Z400. "Reset register is not supported, but you could
still write 6 to 0xcf9" :)
I'd say "6 to 0xCF9" is good enough; rcr_write() in qemu is OK with it
too (including your patch at
<http://thread.gmane.org/gmane.comp.emulators.qemu/195351/focus=195387>.)
Laszlo
