USB2+umass: root mount fails

[M. Warner Losh]

In message: <20090219050200.GA84647 at citylink.fud.org.nz>
            Andrew Thompson <thompsa at FreeBSD.org> writes:
: On Tue, Feb 17, 2009 at 08:54:24AM -0700, M. Warner Losh wrote:
: > In message: <200902170856.11631.hselasky at c2i.net>
: >             Hans Petter Selasky <hselasky at c2i.net> writes:
: > : On Tuesday 17 February 2009, Marcel Moolenaar wrote:
: > : > > But it looks like the old usb code didn't call it either...  I think
: > : > > old code enumerated right away during boot, while the new code defers
: > : > > the enumeration until events can be processed...
: > : >
: > : > Yes, you're right. USB1 used the following:
: > : >
: > : > SYSINIT(usb_cold_explore, SI_SUB_CONFIGURE, SI_ORDER_MIDDLE,
: > : >      usb_cold_explore, NULL);
: > : >
: > : > SI_SUB_CONFIGURE didn't complete before all USB busses
: > : > were enumerated.
: > : 
: > : I would really prefer that first time USB enumeration is not synchronous. This 
: > : has to do with startup timing. It simply wastes a lot of time to wait for all 
: > : the busses to be probed in serial. Sure it works nice with a USB keyboard and 
: > : a USB mouse, but when you have a couple of USB HUBs and +8 devices connected, 
: > : it simply speeds up the boot time so that you reach the root prompt by the 
: > : time you would else have done the mount root mfs.
: > : 
: > : If the mountroot code cannot find the disk, it should sleep and loop.
: > 
: > I think this is a weak argument.  I'm strongly in favor of the usb1
: > behavior here.
: 
: I think its slightly more complex that adding a cold explore task. Most
: of the USB2 periperhel drivers defer a portion of their attach to a
: thread task, a change which needs to be reverted first. As others have
: said both the probe and attach must be synchronous.

That's true too.  The point I was trying to make wasn't that we needed
a cold explore task, but more that usb should know when it is done
with the probe phase and then do what other hot-plug busses have
started doing.

See my recent changes to dev/pccbb for one example.

Warner