4 ms·
From System.Fundamentals.Firmware.FirmwareSupportsUSBDevices: The USB controller and USB devices must be fully enumerated when: * Anything other than the Windo
by mjg59 13y ago
From System.Fundamentals.Firmware.FirmwareSupportsUSBDevices:
The USB controller and USB devices must be fully enumerated when:
* Anything other than the Windows Boot Manager is at the top of the system boot order.
* A boot next variable has been set to boot to something other than the Windows Boot Manager.
* On a system where the Windows Boot Manager is at the top of the list, an error case has been hit, such that the firmware fails over from the Windows Boot Manager to the next item in the list.
* Resuming from hibernate, if the system was hibernated when booted from USB.
* Firmware Setup is accessed.
ie, it's not required for most normal boots on systems that already have Windows installed. System.Fundamentals.Firmware.FirmwareSupportsBootingFromDVDDevice merely states that the system must support booting from DVD, not that it must attempt to by default. And yes, I've observed this behaviour on real hardware.
- kogir 13y agoI believe you, but can you please name and shame? I'd hate to accidentally purchase hardware which by design makes entering firmware setup impossible[1]. With online ordering this isn't always something you can check in advance. [1] I'm assuming that if a working OS install is required to access it, should anything go wrong you're screwed.
- mjg59 13y agoThe Microsoft spec says that any fallback to the Windows rescue environment should trigger full USB enumeration. The Samsung Series 5 I tested had this behaviour, but given I had to return it after managing to kill the firmware I can't give you the exact model number…
- vidarh 13y agoDoes this mean that the hardware is pretty much guaranteed to boot slower if not booting Windows too, in order to do USB initialisation, even when not going to the boot screen?
- mjg59 13y agoApparently, yes, which is something I hadn't noticed before.
- FireBeyond 13y agoI wouldn't have thought so - I'd think that Linux would be perfectly capable of utilizing the same 'fast boot' logic as Windows has. I think it only applies to "getting into a USB boot / install environment".
- mjg59 13y agoThe spec says that the feature should be disabled if any UEFI boot entry other than "Windows Boot Manager" is chosen. Whether that's actually implemented, I don't know.
- gizmo686 13y agoRegardless, it should be possible for the third party loader to claim to be "Windows Boot Manager". I can't imagine that there would be any cryptographic verification that the boot loader is actually "Windows Boot Manager". This is because the crypto logic is essential to check that the binary is signed by a trusted key. This process would happen before the UEFI thinks about entering the boot loader. It would also not make sense for the crypto section to make any associations between the keys and who signed them (apart from giving the user information). Still, it seems like a bad spec to create special cases for named hardware. Hopefully, we will arrive at a standard where the OS can signal if the feature should be disabled, or make it a toggleable setting (which, from what I understand of UEFI, the OS can toggle). Unfourtuantly, depending on how strict MS is with their certification standards, this would prevent the computers from being certified.
- mjg59 13y agoIt's entirely possible to do that, but that's a string that's (often) visible to the user. Now I'd have to remember which "Windows Boot Manager" is Windows and which is Linux.
- deleted 13y ago[deleted]