Re: kernel panic with pccard insert on recent 7.0 CURRENT

In message: <200707160850.46259.jhb_at_freebsd.org>
            John Baldwin <jhb_at_freebsd.org> writes:
: On Sunday 17 June 2007 01:56:59 am M. Warner Losh wrote:
: > In message: <20070617053746.GV4602_at_funkthat.com>
: >             John-Mark Gurney <gurney_j_at_resnet.uoregon.edu> writes:
: > : Warner Losh wrote this message on Sat, Jun 16, 2007 at 21:12 -0600:
: > : > In message: <20070617024935.GU4602_at_funkthat.com>
: > : >             John-Mark Gurney <gurney_j_at_resnet.uoregon.edu> writes:
: > : > : Warner Losh wrote this message on Sat, Jun 16, 2007 at 17:33 -0600:
: > : > : > Also, I'm unclear on the difference between FILTER_STRAY and
: > : > : > FILTER_HANDLED.
: > : > : 
: > : > : The interrupt filter is suppose to return one of FILTER_STRAY or
: > : > : FILTER_HANDLED...  If you _HANDLED it return that, otherwise return
: > : > : _STRAY...  If you need to schedule the ithread, return _HANDLED or'd
: > : > : with _SCHEDULE_THREAD...
: > : > 
: > : > Will _HANDLED cause all the other handlers to not get called, or just
: > : > the stray interrupt code from not happening?
: > : 
: > : It will cause the remaining (not yet called) handlers not to get called...
: > 
: > I'm not sure that's right, especially for edge triggered devices.\
: 
: They shouldn't share interrupts then.  Do we support shared interrupts on edge 
: triggered devices?

We support sharing interrupts on edge triggered devices.  At least it
has worked on FreeBSD 2.2.1 through 6.2.  We have to continue to
support it, and to do that, we can't have HANDLED stop processing.

It is a sad fact of life, but we have to continue to support that.

As an aside, some ISA hardware cannot support sharing of interrupts,
but simple modification of the drivers allows one to share ISA
interrupts.  My company has been doing this successfully for about 12
years, and using FreeBSD to do it for at least the past 10 years.

: > : intr_event_handle calls intr_filter_loop which will return on the first
: > : non-_STRAY handler and return it...  Which intr_event_handle eoi's...
: > :
: > : It looks like this code is designed for level triggered interrupts and
: > : not edge triggered...
: > 
: > Yes.  I'm pretty sure that's wrong.  All ISA and PC Card devices use
: > edge triggered interrupts.  Also, it is inefficient for level
: > triggered interrupts, since two interrupt sources on the same
: > interrupt may trigger at about the same time...
: 
: It works fine since the second device will interrupt again and we will fall 
: through to its routine on the second interrupt.  The idea is that 
: simultaneous interrupts are rare enough that it is worth optimizing the 
: common case.

Actually, PC Card devices aren't necessarily edge triggered, but can
be either edge triggered or level triggered.  They can live in bridges
that are either Edge triggered or level triggered depending on the
topology of the bus they live on.

In any event, the current code is incorrect and needs to be fixed.

Warner