Re: [Qemu-devel] [PATCH v5 0/6] i386: expose floppy-related objects in SSDT

[Roman Kagan]

On Wed, Jan 13, 2016 at 06:49:44PM +0300, Roman Kagan wrote:
> 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.

Ah, I wish I saw your comment
https://bugzilla.redhat.com/show_bug.cgi?id=1212317#c5
I'd probably proceed directly to trying _FDI :)

Roman.