On 10/22/2014 10:07 AM, Marc Zyngier wrote: <snip> >> Hi Andre, >> >> For the convenience of other kernel components, is there anyway to merge >> *parts* of GICv2 and GICv3 at high-level? So others can probe/poke the >> GIC details in the system, which includes the version of GIC. >> >> For instance, I am working a patch to get rid of DT-ACPI in >> virt/kvm/arm/vgic.c file and facing a similar issue as described by >> Claudio. Current vgic.c parses DT-tree then dispatches to vgic-v2.c and >> vgic-v3.c. Getting rid of DT will make dispatching impossible (a >> dilemma). The version info provided by GIC drivers will be helpful for >> this case, at least. > > If you had a chance to read the architecture document (it is > unfortunately not public yet), you'd quickly notice that the similarity > between GICv2 and GICv3 is fairly superficial, specially in the absence > of the GICv2 compatibility regions (they are optional). > Thanks for the explanation. > We have DT/ACPI/whatever for this exact purpose: finding out what the > hardware is. These mechanisms give us structured information that > describe the available HW in great detail, and I will strongly oppose > any form of guess-work. > > Sorry, but I have to ask: what is wrong with the current DT parsing? A bit long story. DT parsing itself was not a problem until recently when ACPI was enabled. It broke KVM because KVM doesn't support ACPI. So we started to add ACPI parsing into KVM code (virt/kvm/arm/, see Alexander Spyridakis' recent patches, very similar to our internal fixes). It turned out to be quite messy due to the if-DT-else-ACPI in arch_timer and vgic code. Additionally kernel does the parsing twice, one in native drivers and the other in KVM, which is unnecessary. My proposal is to get rid of DT-ACPI parsing in KVM completely. We rely on device drivers to provide necessary info, which makes the interface cleaner. arch_timer is very easy to fix (see https://lists.cs.columbia.edu/pipermail/kvmarm/2014-October/011526.html); but GIC is complicated because vgic.c dispatches to vgic-v2 and vgic-v3. My question to Andre was: could GIC drivers provides some info for KVM to query, such as GIC version. This request in fact is to eliminate guess work from KVM's perspective. > > Thanks, > > M. > _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
