Re: ensuring a machine's buses have unique names

[Peter Maydell]

On Thu, 12 Aug 2021 at 12:05, Peter Maydell <peter.maydell@linaro.org> wrote:
>
> What's the right way to ensure that when a machine has multiple
> buses of the same type (eg multiple i2c controllers, multiple
> sd card controllers) they all get assigned unique names so that
> the user can use '-device ...,bus=some-name' to put a device on a
> specific bus?
>
> For instance in hw/arm/xlnx-zynqmp.c, the SoC object creates
> a set of alias properties on the SoC for the sd-bus buses that
> its 4 SD card controllers create. The alias properties are named
> "sd-bus%d" so they are unique. This works, but it's kind of error-prone
> because you need each machine model to remember to create these
> aliases when necessary.
>
> mps3-an524 is an example of a machine that fails to do this
> for its i2c buses, and therefore the user can't usefully
> tell QEMU which bus to plug a command-line created i2c bus into.
>
> Ideally we should make buses get unique names by default
> and also assert() at startup that there aren't any duplicated
> names, I think.
>
> Side note: is there a way to mark a bus as "do not consider
> this when plugging devices where the user did not specify
> the bus themselves" ? Some of the i2c buses on that machine
> are purely internal to the board (eg there's one that has
> the touchscreen controller hanging off it and nothing else),
> and some are "this i2c bus is connected to the expansion port",
> so ideally if no bus is specified we would want to prefer
> the expansion-port i2c bus, not the ones that are internal-only.

Ping, in the hopes anybody has an answer to these...

-- PMM