Clean up MD pollution of bus_dma.h:
--Remove special-case handling of sparc64 bus_dmamap* functions.
Replace with a more generic mechanism that allows MD busdma implementations to generate inline mapping functions by defining WANT_INLINE_DMAMAP in <machine/bus_dma.h>. This is currently useful for sparc64, x86, and arm64, which all implement non-load dmamap operations as simple wrappers around map objects which may be bus- or device-specific.
--Remove NULL-checked bus_dmamap macros. Implement the
equivalent NULL checks in the inlined x86 implementation. For non-x86 platforms, these checks are a minor pessimization as those platforms do not currently allow NULL maps. NULL maps were originally allowed on arm64, which appears to have been the motivation behind adding arm[64]-specific barriers to bus_dma.h, but that support was removed in r299463.
--Simplify the internal interface used by the bus_dmamap_load*
variants and move it to bus_dma_internal.h
--Fix some drivers that directly include sys/bus_dma.h
despite the recommendations of bus_dma(9)
Reviewed by: kib (previous revision), marius
Differential Revision: https://reviews.freebsd.org/D10729