bus_dma(9) cleanup.
o Enforce TX/RX descriptor ring alignment. NS data sheet says the
controller needs 4 bytes alignment but use 16 to cover both SiS and NS controllers. I don't have SiS data sheet so I'm not sure what is alignment restriction of SiS controller but 16 would be enough because it's larger than the size of a TX/RX descriptor. Previously sis(4) ignored the alignment restriction.
o Enforce RX buffer alignment, 4.
Previously sis(4) ignored RX buffer alignment restriction.
o Limit number of TX DMA segment to be used to 16. It seems
controller has no restriction on number of DMA segments but using more than 16 looks resource waste.
o Collapse long mbuf chains with m_collapse(9) instead of calling
expensive m_defrag(9).
o TX/RX side bus_dmamap_load_mbuf_sg(9) support and remove
unnecessary callbacks.
o Initial endianness support.
o Prefer local alignment fixup code to m_devget(9).
o Pre-allocate TX/RX mbuf DMA maps instead of creating/destroying
these maps in fast TX/RX path. On non-x86 architectures, this is very expensive operation and there is no need to do that.
o Add missing bus_dmamap_sync(9) in TX/RX path.
o watchdog is now unarmed only when there are no pending frames
on controller. Previously sis(4) blindly unarmed watchdog without checking the number of queued frames.
o For efficiency, loaded DMA map is reused for error frames.
o DMA map loading failure is now gracefully handled. Previously
sis(4) ignored any DMA map loading errors.
o Nuke unused macros which are not appropriate for endianness
operation.
o Stop embedding driver maintained structures into descriptor
rings. Because TX/RX descriptor structures are shared between host and controller, frequent bus_dmamap_sync(9) operations are required in fast path. Embedding driver structures will increase the size of DMA map which in turn will slow down performance.