svn commit: r215544 - head/sys/kern

[Jung-uk Kim]

On Friday 19 November 2010 05:16 pm, John Baldwin wrote:
> On Friday, November 19, 2010 5:03:25 pm Jung-uk Kim wrote:
> > On Friday 19 November 2010 04:46 pm, John Baldwin wrote:
> > > On Friday, November 19, 2010 4:31:44 pm Attilio Rao wrote:
> > > > 2010/11/19 John Baldwin <jhb at freebsd.org>:
> > > > > On Friday, November 19, 2010 4:09:28 pm Jung-uk Kim wrote:
> > > > >> On Friday 19 November 2010 02:43 pm, Attilio Rao wrote:
> > > > >> > Author: attilio
> > > > >> > Date: Fri Nov 19 19:43:56 2010
> > > > >> > New Revision: 215544
> > > > >> > URL: http://svn.freebsd.org/changeset/base/215544
> > > > >> >
> > > > >> > Log:
> > > > >> >   Scan the list in reverse order for the shutdown
> > > > >> > handlers of loaded modules. This way, when there is a
> > > > >> > dependency between two modules, the handler of the
> > > > >> > latter probed runs first.
> > > > >> >
> > > > >> >   This is a similar approach as the modules are unloaded
> > > > >> > in the same linkerfile.
> > > > >> >
> > > > >> >   Sponsored by:     Sandvine Incorporated
> > > > >> >   Submitted by:     Nima Misaghian <nmisaghian at
> > > > >> > sandvine dot com> MFC after:        1 week
> > > > >>
> > > > >> Hmm...  It is not directly related but I was thinking
> > > > >> about doing similar things for sys/kern/subr_bus.c.  What
> > > > >> do you think about the attached patch?
> > > > >
> > > > > Hmm, the patches for suspend and resume that I had for this
> > > > > took the opposite order, they did suspend in forward order,
> > > > > but resume in backwards order. Like so:
> > > > >
> > > > > --- //depot/vendor/freebsd/src/sys/kern/subr_bus.c
> > > > > 2010-11-17 22:30:24.000000000 0000 +++
> > > > > //depot/user/jhb/acpipci/kern/subr_bus.c    2010-11-19
> > > > > 17:19:02.000000000 00 @@ -3426,9 +3429,9 @@
> > > > >        TAILQ_FOREACH(child, &dev->children, link) {
> > > > >                error = DEVICE_SUSPEND(child);
> > > > >                if (error) {
> > > > > -                       for (child2 =
> > > > > TAILQ_FIRST(&dev->children); -
> > > > > child2 && child2 != child; -                           
> > > > > child2 = TAILQ_NEXT(child2, link)) +                      
> > > > > for (child2 = TAILQ_PREV(child, device_list, link); +
> > > > >      child2 != NULL;
> > > > > +                            child2 = TAILQ_PREV(child2,
> > > > > device_list, link)) DEVICE_RESUME(child2);
> > > > >                        return (error);
> > > > >                }
> > > > > @@ -3447,7 +3450,7 @@
> > > > >  {
> > > > >        device_t        child;
> > > > >
> > > > > -       TAILQ_FOREACH(child, &dev->children, link) {
> > > > > +       TAILQ_FOREACH_REVERSE(child, &dev->children,
> > > > > device_list, link) { DEVICE_RESUME(child);
> > > > >                /* if resume fails, there's nothing we can
> > > > > usefully do... */ }
> > > > >
> > > > > (Likely mangled whitespace.)
> > > > >
> > > > > I couldn't convince myself which order was "more" correct
> > > > > for suspend and resume.
> > > >
> > > > Considering loading in starting point, I think suspend should
> > > > go in reverse logic and resume in the same module load logic.
> > > > So that dependent modules are suspended first and resumed
> > > > after. Don't you agree?
> > >
> > > These are devices, and the ordering here is the order of
> > > sibling devices on a given bus.  That is, if you have a PCI bus
> > > with two em interfaces, does it really matter if em0 suspends
> > > before em1 vs after em1?  I think it actually doesn't matter. 
> > > The passes from the multipass boot probe might make some sense
> > > to order on. However, I don't think the order of siblings on a
> > > bus is meaningful for suspend and resume (which is why I've
> > > never committed the above patches).
> > >
> > > Specifically, there is no dependency relationship between
> > > siblings on a bus. Certain buses may in fact have a dependency
> > > order of sorts (vgapci0 comes to mind), but those buses should
> > > manage that. There is no generic dependency between siblings
> > > that should be encoded into subr_bus.c
> >
> > Generally siblings don't interact with each other directly, no.
> > However, some modern chipsets *do* have strong relationship.  For
> > example, some chipsets reference SMB controller to get current
> > configuration, e.g., function A depends on function B on the same
> > chip.
>
> That may be true, but that is not generic to all buses and devices.
> That isn't even really generic to PCI.  If there are specific
> instances where there are dependencies, the drivers for that
> hardware should manage that.  If specific buses have specific
> orders, then they can manage that order explicitly in their own
> suspend and resume routines. However, I don't see a valid reason
> for enforcing a particular order among siblings for all devices. 
> We certainly do enforce some orders with respect to children and
> parents (parents attach first and resume first, children detach
> first and suspend first, PCI even mandates this for powering down a
> bus), but the same is not true for siblings.

It may be unnecessary but I like consistency. ;-)

Jung-uk Kim