CAM breaks USB [was Re: USB causing boot to hang]

[Steve Kargl]

On Fri, Dec 06, 2019 at 07:09:55PM -0500, Alexander Motin wrote:
> On 06.12.2019 18:41, Steve Kargl wrote:
> > On Fri, Dec 06, 2019 at 06:15:32PM -0500, Alexander Motin wrote:
> >> On 06.12.2019 17:52, Steve Kargl wrote:
> >>> On Fri, Dec 06, 2019 at 03:33:09PM -0700, Warner Losh wrote:
> >>>> On Fri, Dec 6, 2019 at 3:31 PM Steve Kargl <sgk at troutmask.apl.washington.edu>
> >>>> wrote:
> >>>>> The problem seems to be caused 355010.  This is a commit to
> >>>>> fix CAM, which seems to break USB.
> >>>>>
> >>>> Yes. mav@ made this change...
> >>>>
> >>> src/UPDATING seems to be missing an entry about CAM breaking USB.
> >>
> >> And also that moon is made of cheese. :-\
> > 
> > Not sure what you mean. 
> 
> I mean that if we are going to write there random fairy-tales, then I
> prefer my moon.
> 
> If serious, then my change did not change semantics of any existing
> tunables, only the way some of them are implemented, so there was
> nothing to write in UPDATING.

The system boots at 355009.
The system hangs at 355010.

How about adding:  After revision 355010, the cam subsystem may cause
the usb subsystem to hang during boot.  It is recommended to disable usb.

You even hint at problems in your original commit message.

The system is at work and unattended until Monday.

-- 
Steve