Re: [Qemu-ppc] [PATCH 7/8] openpic: add missing timer fields to vmstate_openpic_timer

[David Gibson]

On Tue, Sep 19, 2017 at 08:50:49PM +0100, Mark Cave-Ayland wrote:
> On 18/09/17 23:44, David Gibson wrote:
> 
> > So, adding new things to the migration stream always requires some
> > thought.  The commit message should contain a rationale for why the
> > proposed representation is a good one.  In particular is it one that's
> > unlikely to be difficult if the device changes internal details in
> > future.  When possible it's best to stick to architected documented
> > state of the modelled hardware, though I can see you're probably going
> > to need some extras in this case.
> 
> Yes, I think that's the case here. Definitely the timer can't be armed
> correctly without origin_time, and if qemu_timer_active isn't present
> and migration occurs with an active timer then a subsequent call to
> openpic_tmr_get_timer() will be incorrect. Does that sound right to
> you?

You'll certainly need some sort of time variable, which could be
expressed in various ways equivalently.  I don't know if you'll need
an explicit extra "active" boolean - are there any openpic registers
which would indicate if a timer is active?  It's generally best to
represent state using documented forms from the hardware whenever
possible.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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