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.
