CVS log for src/sys/arch/mac68k/obio/espvar.h

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Rework avdma to fix PR port-mac68k/56131 as well as add synchronous
transfer support.

According to analysis by Michael Zucca, PSC (DMAC for Quadra/Centris AV)
seems to require that DMA buffer is
  (1) aligned to 16-byte boundaries, and
  (2) multiple of 16 bytes in size.
If the buffer does not satisfy these constraints, esp.c rev 1.63 and
prior carry out partial PIO to align or shave off it.

However, partial PIO does not always work correctly for combination of
NCR53C94 and PSC, which results in failures observed as port-mac68k/56131.

Also, PIO spoils synchronous transfer, which is timing critical.

Therefore, for buffers that do not satisfy the boundary conditions,
completely stop using PIO and use DMA with ``bounce'' buffers.

This fixes port-mac68k/56131 and enables sync transfer as a big bonus.

Note that bounce DMA does not hurt performance at all. For filesystem
and swap I/O, buffers always satisfy the constraints above, and bounce
DMA is necessary only
  (a) when disk is attached, or
  (b) for special utilities like fsck(8) or fdisk(8),
as far as I can tell.

Also:

- Stop providing ``DMA-friendly'' sc_imess and sc_omess; transfer for
  MSGIN or MSGOUT does not almost certainly satisfy boundary condition
  (2). Again, this does not affect performance at all.

- SCSI bus frequency is 20MHz (i.e., 5MB/s for sync transfer) for AV
  models, according to ``Quadra 840AV Service Source''.

Mostly merge changes from HEAD upto 20200411

PR port-mac68k/24883

Support DMA xfer for SCSI adapter of AV Mac (660/840AV), written by
Michael Zucca.

This improves disk I/O performance by nearly one order of magnitude.
In addition, interrupt storm due to heavy disk PIO is resolved.

I'm deeply grateful to Michael Zucca for his analysis of DMA engine
and submission of PR. I also thank Izumi Tsutsui (useful comments on
port-mac68k@) and Martin Husemann (test on 660AV).

PR port-mac68k/24883

Style-only changes in preparation to import AV DMA code:

- G/C unused from esp_softc
- clean up headers:
    - prefer <sys/bus.h> over <machine/bus.h>
    - G/C unused
    - sort
- staticify private functions and variables
- stop using inline qualifier for functions called via function pointers
- use C99 initializer
- provide bus_space_vaddr(9) and use it, instead of using member of
  bus_handle_t directly
- use uint*_t:
    - u_char --> uint8_t
    - u_int*_t --> uint*_t
- use proper names from ncr53c9xreg.h instead of magic numbers
- and some KNF, and etc.

No functional changes intended.

Sync with HEAD.

Split device_t/softc for MI ncr53c9x and some related devices,
with various cleanup.

Pull up revision 1.6 (requested by briggs):
 Improve performance of the pseudo-DMA mode of the esp driver, and handle
 residual FIFO data on write.

Sync with HEAD

Rework the esp driver a little bit to improve performance.  This requires
an ugly bit where we record the value of a2 while handling a "nofault" bus
error in locore.s in order to know how far the transaction got before a
disconnect (see esp.c comments for more details on this).
Also get rid of a loop (and delay()!) in the interrupt routine--hinted at
and researched by Chas Williams <chas@cmf.nrl.navy.mil>.

Pull rev 1.5 up from trunk (briggs)

Forgot a declaration in last change to esp.c.

Pull rev 1.4 up from trunk (briggs)

A first cut at faster SCSI for non-AV quadras.  Could probably perform better,
but is a marked improvement.  This takes advantage of a pseudo-DMA hardware
hack of Apple's that exposes a 16-bit register that the Apple-designed
memory controller acts like a DMA controller and handshakes into or out
of the FIFO.  Wierd.

Merge in changes from The Trunk, partially just reimplementing newarp.

mac68k-specific portion of m.i. ncr53c9x driver.

Improve reliability on my Q700, at least.  Was getting the occasional
glitch--an extra byte on occasion.

Interrupt-driven, but slow, NCR 53c96 driver for the 040-based macs.  Contains
some guesses for the machines that have two of these buggers (I don't have
such a machine).  This driver is a copy of the sparc/alpha esp with a
minimum of changes--after we get it performing a bit more respectably,
we should see about re-normalizing the sources.