On Sat, 24 Sept 2022 at 00:42, Patrick Venture <venture@google.com> wrote:
> On Thu, Sep 22, 2022 at 8:21 PM Jason Wang <jasowang@redhat.com> wrote:
>>
>> On Thu, Sep 22, 2022 at 8:35 PM Peter Maydell <peter.maydell@linaro.org> wrote:
>> > 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?
I think what Jason is suggesting is that that should depend on what
the real hardware does. On a physical board, if the guest sets the
MAC address, and then you power-cycle the hardware, does the MAC
that it set still persist after powercycle ? Does the guest writing
to these MAC registers correspond to writing to an EEPROM ?
Thanks, Peter - we've reached out to the vendor off-list to seek out some details, I'll update this with a v2 when I get an answer.
thanks
-- PMM