Re: 3c59x vortex_timer rt hack (was: rt20 patch question)

[Andrew Morton <akpm@osdl.org>]

Steven Rostedt <rostedt@goodmis.org> wrote:
>
> 
> 
> On Fri, 12 May 2006, Andrew Morton wrote:
> 
> > >
> > > The vortex_timer is a timeout,
> >
> > err, it's actually a function.
> 
> OK, I meant vp->timer

That's a kernel timer.

> >
> > > will it go off often?
> >
> > Every five seconds if the cable's unplugged.  Every 60 seconds otherwise.
> >
> 
> OK, so the function is a service and not a fixup (or both).  Hmm, so
> latency is an issue.

yup.  It's been five years, sorry - I'm struggling to remember why
vortex_timer() needs to block the interrupt handler.

The chip is fairly stateful - that EL3WINDOW() thing selects a particular
register bank and needs protection against other register readers.  But we
should avoid running EL3WINDOW() in the rx and tx interrupt handlers anyway
- iirc the chip is designed to permit that.

Is tricky.

How come -rt cannot permit disable_irq() in there?

(I think the _reason_ it's disable_irq() is, yes, because it's infrequent
and because it can hold off interrupts for a long time if we use
spin_lock_irq())