busdma: emit a warning for use of filters

[mhorne]

Summary

Filter functions are deprecated, and unused in the tree. If either of
the filter or filterarg arguments to bus_dma_tag_create() are non-NULL,
print a warning.

This is a direct commit to stable/14.

[emaste]

sys/arm/arm/busdma_machdep.c

403

maybe "use of busdma filters"?

Although perhaps the man page reference is enough of a clue

[jhb]

It's a shame we can't print out the name of the offending device. Probably want this in stable/13 as well.

[emaste]

It's a shame we can't print out the name of the offending device.

Indeed - I'm not particularly familiar with this interface but went looking to see if there was a reasonable way to give more information. We could perhaps print a backtrace? In practice though if a user sees this message asking for a (perhaps verbose) dmesg should be sufficient, I'd think.