the MCA DMA controller access. This also means we gain >16MB RAM support.
While here, overhaul the driver to saner state, especially:
* simplify and clean the attach code a lot, and support the 'drive'
locator
* pass proper dev_t to readdisklabel() - formerly, the passed value was
completely broken (used incorrect major and wrong minor), but worked
by accident
* worker thread is now spawned per controller, rather than per-drive;
i/o cannot be done concurrently by different drivers, only one
i/o can be pending at any time
* simplify the command queue code, just sleep appropriately when
!poll case, g/c 'async' code formerly needed, move the bio code
from ed_mca.c to edc_mca.c:edc_bio()
* put all string arrays used by edc_dump_status_block() within #ifdef EDC_DEBUG,
and use numbers instead if it's not defined; this cuts object size by 5KB
* other misc cleanups
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