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[v5,5/5] hw/nvram/eeprom_at24c: Make reset behavior more like hardware

Message ID 20230128060543.95582-6-peter@pjd.dev (mailing list archive)
State New, archived
Headers show
Series hw/nvram/eeprom_at24c: Cleanup + FRUID EEPROM init example | expand

Commit Message

Peter Delevoryas Jan. 28, 2023, 6:05 a.m. UTC
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>
Reviewed-by: C├ędric Le Goater <clg@kaod.org>
Reviewed-by: Corey Minyard <cminyard@mvista.com>
 hw/nvram/eeprom_at24c.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)
diff mbox series


diff --git a/hw/nvram/eeprom_at24c.c b/hw/nvram/eeprom_at24c.c
index 05598699dc2b..3328c3281435 100644
--- a/hw/nvram/eeprom_at24c.c
+++ b/hw/nvram/eeprom_at24c.c
@@ -184,18 +184,6 @@  static void at24c_eeprom_realize(DeviceState *dev, Error **errp)
     ee->mem = g_malloc0(ee->rsize);
-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) {
@@ -213,6 +201,16 @@  void at24c_eeprom_reset(DeviceState *state)
+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),