usb/113977: [request] Need a way to set mode of USB disk's write cache

[Dieter]

In message <200908311214.n7VCEBJ2046645 at freefall.freebsd.org>, gavin at FreeBSD.org writes:
> Synopsis: [request] Need a way to set mode of USB disk's write cache
> 
> State-Changed-From-To: suspended->feedback
> State-Changed-By: gavin
> State-Changed-When: Mon Aug 31 12:07:21 UTC 2009
> State-Changed-Why: 
> To submitter: Sorry that this PR has not been looked at since
> submission.  If your external device supports changing write
> cache, I think it should be visible with "camcontrol modepage da0 -m 8".
> If that doesn't work, I don't know if there is any way you can
> achieve what you want to do.
> 
> 
> Responsible-Changed-From-To: freebsd-usb->gavin
> Responsible-Changed-By: gavin
> Responsible-Changed-When: Mon Aug 31 12:07:21 UTC 2009
> Responsible-Changed-Why: 
> Track
> 
> http://www.freebsd.org/cgi/query-pr.cgi?pr=113977

With:  umass0: <Prolific Technology Inc. ATAPI-6 Bridge Controller, class 0/0, rev 2.00/0.01, addr 2> on uhub4

# camcontrol modepage da0 -l
0x2f

# camcontrol modepage da0 -m 8
IC:  0
ABPF:  0
CAP:  0
DISC:  0
SIZE:  0
WCE:  0
MF:  0
RCD:  0
Demand Retention Priority:  0
Write Retention Priority:  0
Disable Pre-fetch Transfer Length:  0
Minimum Pre-fetch:  0
Maximum Pre-fetch:  0
Maximum Pre-fetch Ceiling:  0

# camcontrol modepage da0 -m 0x8 -e
camcontrol: no editable entries


With:  umass0: <JMicron USB to ATA/ATAPI Bridge, class 0/0, rev 2.00/1.00, addr 2> on uhub1

# camcontrol modepage da0 -l

gives no response (just a new shell prompt)

# camcontrol modepage da0 -m 0x8
camcontrol: error sending mode sense command

I tried several other values for -m with the same results.