Make dpaa2 software portal handoff time a sysctl tunable

[flo_purplekraken.com]

Summary

When debugging the new dpaa2 driver, it is very handy to be able to change the software portal handoff time without recompiling the kernel.
This commit makes the handoff time a sysctl tunable, so it can be changed at runtime.

[dsl]

sys/dev/dpaa2/dpaa2_io.c

84

1000 is too small taking into account DMA tag per buffer (https://codeberg.org/dsl/freebsd-src/commit/2e198edf2e98bf7c077de9a21853d23c74e61701). I'm going to have the IRQ holdoff at 5000 by default after merging those changes, i.e. 5ms instead of 120us. 10000 would do, I guess.

229

Can be "static void", I think. There's no place in the function where actual error is returned.

sys/dev/dpaa2/dpaa2_io.h

104

I'd name it as "irq_holdoff" with /* ms */ given in the following comment. Could you also add /* sysctl(9) */ comment above? It'd clear doubts about this field.

sys/dev/dpaa2/dpaa2_swp.c

188

It might be a good idea to check both "sc" and "sc->swp_desc".

301

I'd put it as "from the device context".

[flo_purplekraken.com]

Incorporated review feedback

[flo_purplekraken.com]

sys/dev/dpaa2/dpaa2_swp.c

188

swp_desc is not a pointer, but an embedded struct, so it cannot be NULL.

[dsl]

sys/dev/dpaa2/dpaa2_swp.c

188

ah, yes, that's right, sorry for the noise