From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grant Likely Subject: Re: [RFC v2] ARM VM System Specification Date: Wed, 11 Jun 2014 13:02:27 +0100 Message-ID: References: <20140328184517.GA27219@cbox> <539754E5.3030408@redhat.com> <4478880.643uirndOk@wuerfel> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4478880.643uirndOk@wuerfel> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Arnd Bergmann Cc: Peter Maydell , Ian Campbell , kvm-devel , "cross-distro@lists.linaro.org" , "marc.zyngier@arm.com" , Michael Casadevall , Rob Herring , "xen-devel@lists.xen.org" , Stefano Stabellini , Paolo Bonzini , "kvmarm@lists.cs.columbia.edu" , "linux-arm-kernel@lists.infradead.org" List-Id: xen-devel@lists.xenproject.org On Wed, Jun 11, 2014 at 12:58 PM, Arnd Bergmann wrote: > On Wednesday 11 June 2014 12:33:30 Grant Likely wrote: >> On Tue, Jun 10, 2014 at 7:56 PM, Paolo Bonzini wrote: >> > Il 10/06/2014 20:08, Peter Maydell ha scritto: >> > >> >> On 10 June 2014 18:04, Christopher Covington 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. >> >> In practical terms, yes the VM needs to provide an RTC interface, but >> I don't think it needs to appear in this spec, even if the kernel >> accesses it directly. Portable images should use the UEFI service. > > It sounds like it should be in the spec then, if we want people building > portable images to include the efi-rtc driver. Fair enough. g.