Am 26.11.2018 um 20:50 schrieb Christoph Hellwig:
On Thu, Nov 22, 2018 at 10:11:33AM +1300, Michael Schmitz wrote:
Christoph,
for Atari SCSI, commands can only be merged if the physical addresses
of all buffers are contiguous (limitation of the Falcon DMA engine).
Documentation/scsi/scsi_mid_low_api.tx does not spell out whether that
is the case.
Atari SCSI disables scatter/gather, so if that's sufficient to cue
midlevel or bio to not undertake any merging, the flag is no longer
needed.
Yes, if scatter/gather is disable (sg_tablesize == 1 or 0), there will
just be a single, contiguos segment up to .max_sectors, which might
straddle a page boundary if it is larger than PAGE_SIZE. If that is
ok for the ata SCSI hardware we can remove the DISABLE_CLUSTERING
setting.
No requirements for DMA segments to be page aligned or not cross a page
boundary - max. 255 sectors for Falcon (and the driver will fall back to
PIO if that's exceeded IIRC).
No problem removing the setting - probably best if Finn queues that
change for all NCR5380 drivers that can cope with it.
Cheers,
Michael
