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

[Dr. David Alan Gilbert]

* Peter Maydell (address@hidden) wrote:
> On 9 November 2018 at 17:19, Corey Minyard <address@hidden> wrote:
> > On 11/9/18 9:02 AM, Peter Maydell wrote:
> >> The data provided by the caller is only the initialization
> >> data. So I think the device should create its own memory
> >> to copy that init data into, and migrate that ram, not
> >> wherever the initialization data lives. (Currently
> >> this "copy the data into our own ram" happens in the
> >> smbus_eeprom_init() wrapper, but we should do it in the
> >> device realize function instead.)
> >
> >
> > That's what I would like, but should I get rid of the "DEFINE_PROP_PTR"?
> > I don't know the value of creating a properly like this, since the user
> > can't set it and can't see it.  Plus the comments in the code say that
> > it should be gotten rid of at some point.
> >
> > But if I store off the initialization data and keep the actual data in
> > a separate memory created by the realize function, that should work
> > find.
> 
> Well, you still have to pass the init data to the device
> somehow, so I think a pointer property is not a terrible
> way to do that.
> 
> >> Also there seem to be unresolved questions about what happens
> >> on reset -- should the EEPROM revert back to the initial
> >> contents? We don't do that at the moment, but this breaks
> >> the usual QEMU pattern that reset is as if you'd just
> >> completely restarted QEMU.
> >
> >
> > I would consider this part of the hardware, like data on a disk drive,
> > so it seem better to leave it alone after a reset.  But it's not quite
> > the same.  So I'm not sure.
> 
> 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.

Dave


> thanks
> -- PMM
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK