* Peter Maydell (peter.mayd...@linaro.org) wrote: > On Fri, 5 Jul 2019 at 11:13, Paolo Bonzini <pbonz...@redhat.com> wrote: > > > > On 05/07/19 11:58, Peter Maydell wrote: > > > On Fri, 5 Jul 2019 at 10:48, Paolo Bonzini <pbonz...@redhat.com> wrote: > > >> You're right, the compatibility causes wrong behavior for the default > > >> -rtc settings (the RC pauses across migration). The right thing to do > > >> would be to store the base rather than the offset: that is, you store > > >> the time at which LR was written. Then the offset is s->lr - s->base > > >> and it's independent of the machine on which the rtc_clock is being read. > > > > > > Right. How do we handle this for back-compat purposes? I guess > > > we need to have a new migration subsection, so if it's present > > > it has the 'base' value and we ignore the 'offset' in the > > > main migration data, and if it's not present we assume an > > > old->new migration and use the existing offset code. New->old > > > migration would not be possible as the new subsection is > > > always-present. > > > > Yes, something like that but I would just bump the version. Version 1 > > has the old meaning for the first field, version 2 has the new meaning. > > Yeah, we could do that. I thought we preferred to avoid using > version-numbers for migration though these days ? (cc'ing DG > in case he has an opinion.)
Right. Add a subsection, make the subsection only be sent if you're on a new machine type. (I'm currently getting my head around our x86 RTC code because of a bug I've been handed involving RTCs and migration; the expectations and the behaviours are not obvious at all). Dave > > And also, since our brains are fresh on pl031... currently s->lr is > > always 0; besides the bug that writing RTC_LR should update it, the > > datasheet says the counter counts up from 1 so perhaps at startup s->lr > > should be set to a nonzero value? That would be > > qemu_ref_timedate(QEMU_CLOCK_VIRTUAL) - 1. > > The 'summary of RTC registers' section in the datasheet says > that RTCLR's reset value is zero... > > thanks > -- PMM -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
