Re: [Qemu-devel] [PATCH 3/3] i2c: Add vmstate handling to the smbus eeprom

[Peter Maydell]

On 12 November 2018 at 17:38, Dr. David Alan Gilbert
<address@hidden> wrote:
> * Peter Maydell (address@hidden) wrote:
>> That would require us to support backing it properly with a block
>> device, like the pflash flash devices, I think. (This would
>> be the long term way to be able to dump the pointer property,
>> in favour of a block backend property.)
>
> There's a number of separate questions:
>
> a) Can the guest write to the EEPROM or are we just treating it as a
> ROM?
> b) If a guest writes to the EEPROM and then resets does the data stay
> there [I'd expect so, it's an EEPROM]
> c) It the guest writes to the EEPROM and then quits qemu and restarts
> does the data stay there?
> d) If the guest is migrated does it keep the data it's written - I'd say
> it must because otherwise it would get confused.
>
> (c) is where it starts looking like a pflash - which does get a bit
> messy.

My view is that the answers to b and c should always be the same:
resetting QEMU with a system reset should look the same as if
you stopped QEMU and restarted it. (Our only kind of system
reset is an emulation of a hard powercycle.)

In this case, the answer to "a" is currently "yes, it can write to it",
though whether any guest takes advantage of that is a different
question.

thanks
-- PMM