Re: [PATCH 1/3] X86: Revamp reboot behaviour to match Windows more closely

Matthew Garrett
2010-12-09T22:58:44Z

On Thu, Dec 09, 2010 at 02:53:35PM -0800, H. Peter Anvin wrote:
> On 12/09/2010 02:51 PM, Matthew Garrett wrote:
>> I'm afraid I don't understand your argument. The date cutoff would be on
>> the order of 2001 (anything after this will have been tested with XP).
>> The spec that defines this behaviour only came into existence in August
>> 2000, and any older hardware will be missing the flag that indicates
>> that this feature is supported. It doesn't seem realistic to believe
>> that there's any real body of hardware that sets the flag but otherwise
>> has a broken implementation.
>>
>
> 2001 is probably a good date, then.
>
> It's pretty safe you'll see the bit being set on systems which are older
> than that, even if it was not defined at the time it was created -- just
> being garbage. That's par for the course in BIOS land.

There's a revision field in the FADT. They'd need to simultaneously
provide an incorrect revision *and* by pure luck set the 10th bit of a
32-bit register. Is it possible? Yes. Is it likely? No, and I don't see
a benefit in adding extra code to force hardware into a less-tested
configuration.

--
Matthew Garrett | mjg59@srcf.ucam.org