On Thu, Sep 22, 2022 at 8:35 PM Peter Maydell <peter.maydell@linaro.org> wrote:
>
> On Thu, 22 Sept 2022 at 00:47, Patrick Venture <venture@google.com> wrote:
> >
> > The MAC address set from Qemu wasn't being saved into the register space.
> >
> > Reviewed-by: Hao Wu <wuhaotsh@google.com>
> > Signed-off-by: Patrick Venture <venture@google.com>
>
> > @@ -112,6 +115,18 @@ static void emc_reset(NPCM7xxEMCState *emc)
> >
> > emc->tx_active = false;
> > emc->rx_active = false;
> > +
> > + /* Set the MAC address in the register space. */
> > + uint32_t value = (emc->conf.macaddr.a[0] << 24) |
> > + (emc->conf.macaddr.a[1] << 16) |
> > + (emc->conf.macaddr.a[2] << 8) |
> > + emc->conf.macaddr.a[3];
> > + npcm7xx_emc_write(emc, REG_CAMM_BASE * sizeof(uint32_t), value,
> > + sizeof(uint32_t));
> > +
> > + value = (emc->conf.macaddr.a[4] << 24) | (emc->conf.macaddr.a[5] << 16);
> > + npcm7xx_emc_write(emc, REG_CAML_BASE * sizeof(uint32_t), value,
> > + sizeof(uint32_t));
>
> If I understand correctly, the issue here is that emc->regs[REG_CAMM_BASE]
> and emc->regs[REG_CAML_BASE] aren't being reset correctly. If so,
> I think the better approach is to simply reset them here, without
> going through the register-write function, the same way we already
> do for the handful of other registers which have non-zero reset values.
> That's the way other devices seem to do it.
>
> A question to which I don't know the answer: if the guest writes to
> the device to change the MAC address, should that persist across
> reset, or should reset revert the device to the original MAC address
> as specified by the user on the command line or whatever ? At the
> moment you have the former behaviour (and end up storing the MAC
> address in two places as a result -- it would be neater to either
> keep it in only one place, or else have emc->regs[] be the current
> programmed MAC address and emc->conf.macaddr the value to reset to).
>
> I'm not sure we're consistent between device models about that,
> eg the e1000 seems to reset to the initial MAC addr, but the
> imx_fec keeps the guest-set value over resets. Jason, is there
> a recommended "right way" to handle guest-programmable MAC addresses
> over device reset ?
I think it depends on the NIC.
E1000 has a EEPROM interface for providing the MAC address for the
ethernet controller before it can be accessed by the driver during
reset. For modern Intel NICs like E810, it has similar semantics but
using NVM instead of EEPROM. So the current e1000 behaviour seems to
be correct (treat the initiali MAC as the one stored in the EEPROM).
I guess most NIC should behave the same as having a persistent storage
for MAC for the controller during reset, but I'm not sure this is the
case for imx_fec.
So the first time the NIC is realized, it should take the value from the command line. Then later if the guest OS updates it, it should always on reset use that provided value?
(Anyhow, if we change the behaviour we need keep migration compatibility)
Thanks
>
> thanks
> -- PMM
>