Re: [PATCH 0/3] hw/{i2c,nvme}: mctp endpoint, nvme management interface model

[Jeremy Kerr]

Hi Klaus,

[+CC Matt]

> This adds a generic MCTP endpoint model that other devices may derive
> from. I'm not 100% happy with the design of the class methods, but
> it's a start.

Thanks for posting these! I'll have a more thorough look through soon,
but wanted to tackle some of the larger design-points first (and we've
already spoken a bit about these, but rehashing a little of that for
others CCed too).

For me, the big decision here is where we want to run the NVMe-MI
device model. Doing it in the qemu process certainly makes things
easier to set up, and we can just configure the machine+nvme-mi device
as the one operation.

The alternative would be to have the NVMe-MI model run as an external
process, and not part of the qemu tree; it looks like Peter D is going
for that approach with [1]. The advantage there is that we would be
able to test against closer-to-reality "MI firmware" (say, a device
vendor running their NVMe-MI firmware directly in another emulator? are
folks interested in doing that?)

The complexity around the latter approach will be where we split the
processes, and arrange for IPC. [1] suggests at the i2c layer, but that
does seem to have complexities with i2c controller model compatibility;
we could certainly extend that to a "generic" i2c-over-something
protocol (which would also be handy for other things), or go higher up
and use MCTP directly as the transport (say, the serial binding over a
chardev). The former would be more useful for direct firmware
emulation.

My interest is mainly in testing the software stack, so either approach
is fine; I assume your interest is from the device implementation side?

Cheers,


Jeremy

[1]: 
https://github.com/facebook/openbmc/blob/helium/common/recipes-devtools/qemu/qemu/0007-hw-misc-Add-i2c-netdev-device.patch