[src/trunk]: src/sys/arch/mac68k/obio Elucidate why synchronous transfer is d...

[rin <rin%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/3e9a8cf7227c
branches:  trunk
changeset: 1018955:3e9a8cf7227c
user:      rin <rin%NetBSD.org@localhost>
date:      Mon Feb 22 05:23:36 2021 +0000

description:
Elucidate why synchronous transfer is disabled for AV Macs.

Sync negotiation times out when drive advertises that capability:

----
sd1 at scsibus0 target 1 lun 0: <codesrc, SCSI2SD, 6.0> disk fixed
sd1: 16384 MB, 2088 cyl, 255 head, 63 sec, 512 bytes/sect x 33554432 sectors
sd1: sync (160.00ns offset 15), 8-bit (6.250MB/s) transfers
...
sd1(esp0:0:1:0): esp0: timed out [ecb 0x9f7fc4 (flags 0x1, dleft 8, stat 0)], <state 5, nexus 0x9f7fc4, phase(l 1, c 1, p 1), resid 8, msg(q 0,o 80) DMA active>
sd1(esp0:0:1:0): sync negotiation disabled
sd1(esp0:0:1:0): esp0: timed out [ecb 0x9f7fc4 (flags 0x41, dleft 8, stat 0)], <state 5, nexus 0x9f7fc4, phase(l 1, c 1, p 1), resid 8, msg(q 20,o 80) DMA active> AGAIN
sd1: async, 8-bit transfers
----

This is observed for real SCSI drives as well as SCSI2SD (rev 6.0).

Note that this is not a fallout from DMA patch for AV Macs; timeout
takes place even if ``avdma'' code is forcibly disabled.

No binary changes.

diffstat:

 sys/arch/mac68k/obio/esp.c |  9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diffs (30 lines):

diff -r ce935576519e -r 3e9a8cf7227c sys/arch/mac68k/obio/esp.c
--- a/sys/arch/mac68k/obio/esp.c        Mon Feb 22 04:24:41 2021 +0000
+++ b/sys/arch/mac68k/obio/esp.c        Mon Feb 22 05:23:36 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: esp.c,v 1.59 2021/02/22 04:24:41 rin Exp $     */
+/*     $NetBSD: esp.c,v 1.60 2021/02/22 05:23:36 rin Exp $     */
 
 /*
  * Copyright (c) 1997 Jason R. Thorpe.
@@ -81,7 +81,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: esp.c,v 1.59 2021/02/22 04:24:41 rin Exp $");
+__KERNEL_RCSID(0, "$NetBSD: esp.c,v 1.60 2021/02/22 05:23:36 rin Exp $");
 
 #include <sys/types.h>
 #include <sys/param.h>
@@ -327,8 +327,9 @@
                 * No synchronous xfers w/o DMA.
                 *
                 * XXXRO
-                * Also disable synchronous xfers for avdma for now,
-                * by which some disks cannot be read.
+                * Also disable synchronous xfers for AV Macs;
+                * sync negotiation times out when drive advertises that
+                * capability, even if avdma code is forcibly disabled.
                 */
                sc->sc_minsync = 0;
        }