cvs commit: src/sys/cam/scsi scsi_da.c src/sys/dev/usb umass.c usbdevs

[Scott Long]

Matthew Jacob wrote:
>>>
>>>
>>> And how will you distinguish between "not currently enabled" and "not 
>>> supported"?
>>>
>>
>> If WCE is not supported, will the device lie and report the WCE bit as
>> set?
>>
> 
> No. But a device could have it turned off and you wouldn't then infer 
> that you *could*.

I guess I don't follow.  There was a suggestion to read page 8 during 
the da device probe, cache the WCE value, and act on it accordingly
later on.  There was also a suggestion to read the page on demand as
part of the immediate decision to do the SYNC CACHE.  As much of a
hassle as it could be, the latter is likely the better approach as it
eliminates the messy state tracking that you'd have to do on the user.
Who wants to hack up the pass driver to trap mode page writes and then
try to correlate which da device to pass that info on to?  And yeah,
if the device is able to change the state on its own, there is no
way the first approach can work.

Scott