On Thu, Sep 29, 2022 at 8:54 AM Peter Maydell <peter.mayd...@linaro.org> wrote:
> On Thu, 29 Sept 2022 at 16:28, Patrick Venture <vent...@google.com> wrote: > > On Mon, Sep 26, 2022 at 8:45 AM Patrick Venture <vent...@google.com> > wrote: > >>> 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. > > > "No, The EMC driver reset the MAC address registers during boot > cycle/reset." > > OK, I guess that's clear enough. In a real full-software-stack > setup is the MAC address setup usually done by a BIOS/firmware, > or is it done by Linux ? > The MAC address is usually set up in u-boot or by linux. The openbmc stack currently doesn't actually read what the device thinks its mac address is, but it could :) It just sets it blindly. We found this register issue because we were debugging why the MAC address we were setting in the qemu command line had no effect. Turns out, per this patch, we weren't using that value anywhere. But even with that fixed, the firmware didn't care. :) > > > So in that case, we should disregard the value the user sets in > > reset and use the value provided through Qemu. Or, should we just > > not allow Qemu to set the MAC address at all? > > I think that the behaviour for QEMU's model should be that > on reset we should reset the MAC address registers to the > user-provided value. That is, if the guest writes to the > MAC address registers then that does have an effect, but > only until the next reset. > > That gives you reasonably plausible behaviour for both: > (1) you're emulating some guest that always sets up its > own MAC address when it starts up (eg if it's done by > some BIOS-level code that you're running in the guest) > (2) you're booting a guest kernel directly that expects > that the firmware/BIOS/whatever has already set up > a MAC address -- then the MAC address provided by QEMU/the > user fills that role > > More concretely: > * on reset, set the emc->regs[] fields from emc->conf.macaddr > * when using the MAC address, always use emc->regs[], never > emc->conf.macaddr > * to handle the guest writes to the MAC registers, set > emc->regs[], but not emc->conf.macaddr > > Thanks! That actually made it much easier to parse what you wanted to match the behavior :) > Assuming that doesn't break your existing booting workloads, > of course :-) > > thanks > -- PMM >
