Re: SCSI Polled io fixes for mac68k with PDMA enabled.

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

> I've found while working with mac68k that devices that require polled io scsi 
> transfers would fail with sbc pdma (pseudo dma) would fail when reading and 
> writing to the respective device.
> 
> I've found that virtual devices for rascsi and the scsi2sd drives would fail 
> using pdma.  For virtual disks they would fail always when writing to the 
> device, reads were ok.
> 
> For virtual ethernet devices they would fail for reading and writing.

It looks more detailed information is necessary.

- How does it fail?  Lost interrupts?  Generic SCSI xfer errors?

- Does the mac68k sbc (with MI ncr5380sbc) work with other
  real SCSI devices (at least on your machine)?

- Per obio/sbc_obio.c SBC_INTR and SBC_RESELECT are disabled
  on MACIIFX and MACPB500 (maybe no working interrupts).
 https://github.com/NetBSD/src/blob/43d029e4b58545fb46624a260279892a85d8a211/sys/arch/mac68k/obio/sbc_obio.c#L131
  Does PDMA work on other machines (i.e. with working interrupts)?

- Furthermore, why do you check XS_CTL_POLL instead of SBC_INTR in
  sc_options?

- Does the RaSCSI etc. work with GENERIC (not GENERICSBC)?
  I don't know a history why mac68k has both MI ncr5380 (GENERICSBC) and
  the own NCR5380 driver (GENERIC with dev/mac68k5380.c) for years.

- I wonder if these SCSI emulation devices using GPIO controled by
  own software comply various xfer timings defined in SCSI spec.
  (I have a drive with IDE-SCSI converter that emit errors
   on news68k SCSI with MI ncr5380)

- I also wonder if the first byte of write xfer should be written on
  manualy PDMA write, as eps_dma_go() in mac68k/obio/esp.c
 https://github.com/NetBSD/src/blob/43d029e4b58545fb46624a260279892a85d8a211/sys/arch/mac68k/obio/esp.c#L564

--- 
Izumi Tsutsui