Re: [edk2-devel] [PATCH v2 1/2] OvmfPkg/Bhyve: add USB support

["Michael Brown" <mcb30@ipxe.org>]

On 02/07/2021 00:31, Peter Grehan wrote:
>>>>>   bhyve doesn't (and will likely never) support Uhci/Ehci 
>>>>> controllers so those lines can be removed.
>>>>
>>>> Is it possible to pass such a controller by PCI-Passthrough to a VM?
>>>> If it's possible, I would keep these lines.
>>>
>>>   Uhci/Ehci only support legacy interrupts and that isn't supported 
>>> by bhyve PCI passthru.
>>
>> Is that a detail of the current implementation, or a fundamental 
>> limitation in the bhyve architecture?
> 
>   Only two choices ? :) Maybe half way between those points.

When there is no fundamental limitation, i.e. when a future version of 
the hypervisor may be able to support the feature with no changes to the 
firmware, then it would be good practice to leave the drivers enabled. 
Doing so avoids creating an unnecessarily tight coupling between the 
hypervisor and firmware versions.

More importantly: does it even matter that the hypervisor doesn't 
support passthrough of PCI legacy interrupts?  UEFI operates on a 
polling basis, with the only active interrupt being some kind of 
periodic timer.  Where do you see any requirement for legacy interrupts 
in the UHCI/EHCI drivers?

Thanks,

Michael