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Re: [Xen-devel] [RFC v2] ARM VM System Specification

Il 10/06/2014 20:56, Paolo Bonzini ha scritto:
Il 10/06/2014 20:08, Peter Maydell ha scritto:
On 10 June 2014 18:04, Christopher Covington <cov@xxxxxxxxxxxxxx> wrote:
On 06/10/2014 10:42 AM, Peter Maydell wrote:
I just noticed that this doesn't mandate that the platform
provides an RTC. As I understand it, the UEFI spec mandates
that there's an RTC (could somebody more familiar with UEFI
than me confirm/deny that?) so we should probably put one here.

Pardon my ignorance, but what exactly disqualifies Generic Timer
implementations from being used as Real Time Clocks?

So my naive view was that an RTC actually had to have
support for dealing with real (wall) clock time, ie
knowing it's 2014 and not 1970. The generic timers are
just timers. Or am I wrong and UEFI doesn't really
require that?

The real-time clock provides four UEFI runtime services (GetTime,
SetTime, GetWakeupTime, SetWakeupTime).  The spec says that you can
return EFI_DEVICE_ERROR from GetTime/SetTime if "the time could not be
retrieved/set due to a hardware error", but I don't think this is enough
to make these two optional.  By comparison, GetWakeupTime/SetWakeupTime
can also return EFI_UNSUPPORTED.

So I agree that the RTC is required in UEFI.

... that said, just like I thought was the case for the serial console, do we need to specify the exact hardware models?

We can just say that the VM can expect UEFI boot and runtime services to work. This includes variable services, time services, the serial console protocols and more. It's up to the implementation to provide enough devices to support the firmware, and it's out of this spec's scope to specify the firmware's implementation.

I think even the serial devices should be removed.


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