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

[David Brownlee <abs%absd.org@localhost>]

On Thu, 22 Dec 2022 at 11:47, Nathanial Sloss
<nathanialsloss%yahoo.com.au@localhost> wrote:
>
> Hi,
>
> 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.
>
> To address this I've inctrouduced a flag for sbc.4 PDMA_NO_WRITE which would
> fallback consistently to polled io when writing to the deivice.
>
> Also to check the current scsi transfer control flag XS_CTL_POLL and if set it
> would not use PDMA for that particular transfer.
>
> Please see:
>
> ftp.netbsd.org/pub/NetBSD/misc/nat/sbc_poll_fix.diff
>
> Any objections?

Might it be possible to detect this at runtime - potentially by
trapping a timeout and downgrading to polled io?

David