Re: [PATCH v3 5/5] hw/nvram/eeprom_at24c: Make reset behavior more like hardware

[Joel Stanley]

On Tue, 17 Jan 2023 at 23:24, Peter Delevoryas <peter@pjd.dev> 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.
>
> 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
>