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Re: [Qemu-devel] [PATCH v5 0/6] i386: expose floppy-related objects in S
From: |
Roman Kagan |
Subject: |
Re: [Qemu-devel] [PATCH v5 0/6] i386: expose floppy-related objects in SSDT |
Date: |
Wed, 13 Jan 2016 18:49:45 +0300 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Wed, Jan 13, 2016 at 03:36:18PM +0100, Laszlo Ersek wrote:
> On 12/30/15 21:11, Roman Kagan wrote:
> > Windows on UEFI systems is only capable of detecting the presence and
> > the type of floppy drives via corresponding ACPI objects.
>
> I'm late to the party, but please allow me a question:
>
> how did you figure out that UEFI Windows requires this?
>
> In general, what the ACPI specification says is at best a "guideline"
> for Windows. So how did you prove this was a requirement for Windows?
Well, my statement above that Windows on UEFI can detect floppies *only*
via ACPI is probably a bit stronger than I can actually prove but
- Windows on OVMF didn't see floppies before the patch, while Linux did
(by querying CMOS)
- a number of sources on the internet hinted that Windows needed ACPI
assistance for that, e.g.:
https://www.reactos.org/wiki/UEFI#Floppy
https://social.technet.microsoft.com/Forums/windows/en-US/f17db175-d146-4518-b2e9-c12a15031222/legacy-floppy-compatibility-with-uefi-boot?forum=w7itprohardware
https://social.technet.microsoft.com/Forums/windows/en-US/e91ec27b-0c2d-44a3-b949-e77fa810a4c0/windows-7-uefi-fdd-how-to?forum=w7itprohardware
- the links mentioned the need in _FDE object but indicated it only
allowed for successful enumeration of floppies, not the actual access;
I proved that experimentally
- the ACPI spec stated that _FDE went in concert with _FDI so I tried it
and it worked out
Voila. Besides, I later discovered that a similar research had been
carried out for Parallels proprietary hypervisor, with a similar
outcome.
Roman.