Re: [PATCH 2/7] perf: Create a symlink for a PMU

Andi Kleen
2021-06-24T14:24:35Z

> But first off, why is this symlink suddenly needed? What is so special
> about this new hardware that it breaks the existing model?

The driver can be in two modes:

- Driver fully knows the hardware and puts in the correct Linux names

- Driver doesn't know the hardware but is in a fallback mode where it
only looks at a discovery table. There we don't have the correct names,
just an numeric identifier for the different hardware sub components.

In the later mode the numeric identifier is used in sysfs, in the former
case the full Linux name. But we want to keep some degree of Linux user
space compatibility between the two, that is why the full mode creates a
symlink from the "numeric" name. This way the (ugly) identifiers needed
for the fallback mode work everywhere.

-Andi