Re: "legacy" usb stack fixes

On Thursday 11 September 2008 02:44:42 pm Hans Petter Selasky wrote:
> Hi,
> 
> Would anyone object if I make one non-Giant locked CAM bus for all USB2 
> devices? Something like:

Ask scottl_at_, I think he had mentioned having one bus for all USB devices 
before.
 
> static void
> umass_create_cam_bus_sysinit()
> {
>         devq = cam_simq_alloc(1 /* maximum openings */ );
>         if (devq == NULL) {
>                 return (ENOMEM);
>         }
>         umass_global_sim = cam_sim_alloc
>             (&umass_cam_action, &umass_cam_poll,
>             DEVNAME_SIM,
>             NULL /* priv */ ,
>             0 /* unit number */ ,
> #if (__FreeBSD_version >= 700037)
>             &umass_global_mtx /* mutex */ ,
> #endif
>             1 /* maximum device openings */ ,
>             0 /* maximum tagged device openings */ ,
>             devq);
> 
> 	return;
> }
> 
> static void
> umass_destroy_cam_bus_sysuninit()
> {
> 	....
> }
> 
> SYSINIT(&umass_create_cam_bus_sysinit);
> SYSUNINIT(&umass_destroy_cam_bus_sysuninit);
> 
> --HPS
> 
> On Thursday 11 September 2008, M. Warner Losh wrote:
> > In message: <20080911103343.GH1413_at_rink.nu>
> >
> >             Rink Springer <rink_at_freebsd.org> writes:
> > : On Thu, Sep 11, 2008 at 10:13:22AM +0200, Hans Petter Selasky wrote:
> > : > I also see crashes with my new stuff and the umass driver when the USB
> > : > device is un-plugged too early. The backtraces I've got so far does 
not
> > : > indicate a USB problem, though ....
> > :
> > : That is correct, this is a bug in CAM. More specifically, CAM does not
> > : handle the removal of busses well. There are two possible options:
> > :
> > : 1) Obviously, fix CAM to handle this scenarion
> > :    DragonflyBSD seems to have a lot of fixes in this area, which I
> > :    intend to take a look at 'some day' (no thanks to $reallife...)
> >
> > This is the better option.
> >
> > : 2) Create a CAM bus per USB bus
> > :   I think this is reasonable, and it makes a lot more sense than the
> > :    one-bus-per-device approach that we have now. The idea is that
> > :    every USB controller hub creates a CAM bus, and umass(4) attaches to
> > :    this bus instead of creating its own. Of course, until CAM is fixed,
> > :    detaching PCMCIA or equivalent USB cards will still cause panics, but
> > :    it would be a lot better than it is now...
> >
> > This would mitigate the problem, but there's a lot of people that use
> > CardBus USB cards, and they complain to me from time to time of the
> > problem.
> >
> > Fortunately, the wireless broadband cards that are a usb host
> > controller plus usb device in CardBus format aren't affected...
> >
> > : Personally, I'd like to see option 2 implemented in the USB2 stack, as
> > : it avoids the issue and makes a lot more sense from user perspective
> > : (I'm probably onot the only one who gets scared by 'camcontrol devlist'
> > : if you have a single MP3 player which advertises 2 disks :-))
> >
> > It may make good sense for other reasons as well.  Firewire does
> > something similar, and also umass used to do exactly this.  There's
> > also problems right now with huge bus load leading to devices
> > disconnecting and reconnecting for some suck-ass, but common,
> > chipsets.  If things were implemented this way, then there'd be
> > options to silently reconnect the device when it goes away and comes
> > back a few hundred milliseconds later...  Firewire handles this case
> > too, at the expense of never disconnecting the disk, which isn't so
> > good for a thumb drive...
> >
> > Warner
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-- 
John Baldwin