Re: [PATCH v4 5/5] hw/nvram/eeprom_at24c: Make reset behavior more like hardware

[Peter Delevoryas]

On Wed, Jan 25, 2023 at 03:41:30PM -0600, Corey Minyard wrote:
> On Tue, Jan 17, 2023 at 06:42:14PM -0800, Peter Delevoryas wrote:
> > EEPROM's are a form of non-volatile memory. After power-cycling an EEPROM,
> > I would expect the I2C state machine to be reset to default values, but I
> > wouldn't really expect the memory to change at all.
> 
> Yes, I agree, I was actually wondering about this reviewing earlier
> changes.  Thanks for fixing this.

Oh great! I'm glad everyone has agreed with this so far.

- Peter

> 
> Reviewed-by: Corey Minyard <cminyard@mvista.com>
> 
> > 
> > The current implementation of the at24c EEPROM resets its internal memory on
> > reset. This matches the specification in docs/devel/reset.rst:
> > 
> >   Cold reset is supported by every resettable object. In QEMU, it means we 
> > reset
> >   to the initial state corresponding to the start of QEMU; this might differ
> >   from what is a real hardware cold reset. It differs from other resets 
> > (like
> >   warm or bus resets) which may keep certain parts untouched.
> > 
> > But differs from my intuition. For example, if someone writes some 
> > information
> > to an EEPROM, then AC power cycles their board, they would expect the 
> > EEPROM to
> > retain that information. It's very useful to be able to test things like 
> > this
> > in QEMU as well, to verify software instrumentation like determining the 
> > cause
> > of a reboot.
> > 
> > Fixes: 5d8424dbd3e8 ("nvram: add AT24Cx i2c eeprom")
> > Signed-off-by: Peter Delevoryas <peter@pjd.dev>
> > Reviewed-by: Joel Stanley <joel@jms.id.au>
> > ---
> >  hw/nvram/eeprom_at24c.c | 22 ++++++++++------------
> >  1 file changed, 10 insertions(+), 12 deletions(-)
> > 
> > diff --git a/hw/nvram/eeprom_at24c.c b/hw/nvram/eeprom_at24c.c
> > index f8d751fa278d..5074776bff04 100644
> > --- a/hw/nvram/eeprom_at24c.c
> > +++ b/hw/nvram/eeprom_at24c.c
> > @@ -185,18 +185,6 @@ static void at24c_eeprom_realize(DeviceState *dev, 
> > Error **errp)
> >      }
> >  
> >      ee->mem = g_malloc0(ee->rsize);
> > -
> > -}
> > -
> > -static
> > -void at24c_eeprom_reset(DeviceState *state)
> > -{
> > -    EEPROMState *ee = AT24C_EE(state);
> > -
> > -    ee->changed = false;
> > -    ee->cur = 0;
> > -    ee->haveaddr = 0;
> > -
> >      memset(ee->mem, 0, ee->rsize);
> >  
> >      if (ee->init_rom) {
> > @@ -214,6 +202,16 @@ void at24c_eeprom_reset(DeviceState *state)
> >      }
> >  }
> >  
> > +static
> > +void at24c_eeprom_reset(DeviceState *state)
> > +{
> > +    EEPROMState *ee = AT24C_EE(state);
> > +
> > +    ee->changed = false;
> > +    ee->cur = 0;
> > +    ee->haveaddr = 0;
> > +}
> > +
> >  static Property at24c_eeprom_props[] = {
> >      DEFINE_PROP_UINT32("rom-size", EEPROMState, rsize, 0),
> >      DEFINE_PROP_BOOL("writable", EEPROMState, writable, true),
> > -- 
> > 2.39.0
> > 
> >