Re: [Qemu-devel] [PATCH v5 2/3] xlnx-zynqmp-rtc: Add basic time support

[Peter Maydell]

On 26 January 2018 at 01:09, Alistair Francis
<address@hidden> wrote:
> On Thu, Jan 25, 2018 at 3:36 AM, Peter Maydell <address@hidden> wrote:
>> I'm still not sure about having the current_tm struct fields
>> here rather than whatever the hardware's natural representation
>> of the current time is. Can you explain why you think this
>> is the best approach?
>
> This means that the only thing we have to track is the time that the
> user set, either through the QEMU command line arguments as an
> override or the original starting time. Then from there we can always
> calculate the correct offset based on our current time.
>
> I don't see a nicer way, otherwise we need to recalculate the natural
> representation before and after migration using something more
> complex. This way it's always the same logic, we just run it at init
> and after migration.

Doing it this way round means that it gets complicated when the
guest writes to the RTC, though. At the moment I can't see anywhere
that sets the current_tm fields except for reset and post-migration.
Isn't something missing here? I'm wondering if this choice of
migration state is going to paint us into a corner for handling
guest-writes-to-rtc.

thanks
-- PMM