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Re: [Qemu-devel] [PATCH 3/8] fdc: Introduce fdctrl->phase

From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH 3/8] fdc: Introduce fdctrl->phase
Date: Wed, 20 May 2015 09:06:15 +0100

On 20 May 2015 at 08:54, Kevin Wolf <address@hidden> wrote:
> Am 19.05.2015 um 22:57 hat Peter Maydell geschrieben:
>> Yeah, if there's genuinely an underlying state machine that's
>> not completely visible in registers you need to actually model it.
>> You should probably then model the register bits by calculating
>> them from the state rather than by changing them as you go along
>> in parallel with moving the state machine around.
> I think the combination of registers is actually enough to reconstruct
> what state we're in, so it is derived (otherwise I would have fixed a
> bug that I'm not aware of). Adding logic to derive it in a post-load
> handler should be good enough.

That handles migration, which is good. But I still think that
storing the same information in two places in the device
state (phase field and the register fields) is error-prone.
If we want to switch to having a phase field we should calculate
the relevant register bits on demand based on the phase, rather
than keeping both copies of the state in sync manually.

-- PMM

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