svn commit: r247066 - head/sys/dev/ppc

[Gleb Smirnoff]

On Thu, Feb 21, 2013 at 01:09:57PM +0400, Andrey Zonov wrote:
A> > Log:
A> >   Replace splhigh() with critical_enter()/leave() to ensure we write the
A> >   config mode unlock sequence quickly enough. This likely isn't too critical,
A> >   since splhigh() has been a noop for a decade...
A> > 
A> > Modified:
A> >   head/sys/dev/ppc/ppc.c
A> > 
A> > Modified: head/sys/dev/ppc/ppc.c
A> > ==============================================================================
A> > --- head/sys/dev/ppc/ppc.c	Thu Feb 21 00:26:31 2013	(r247065)
A> > +++ head/sys/dev/ppc/ppc.c	Thu Feb 21 00:27:51 2013	(r247066)
A> > @@ -74,6 +74,22 @@ static void ppcintr(void *arg);
A> >  
A> >  #define DEVTOSOFTC(dev) ((struct ppc_data *)device_get_softc(dev))
A> >  
A> > +/*
A> > + * We use critical enter/leave for the simple config locking needed to
A> > + * detect the devices. We just want to make sure that both of our writes
A> > + * happen without someone else also writing to those config registers. Since
A> > + * we just do this at startup, Giant keeps multiple threads from executing,
A> > + * and critical_enter() then is all that's needed to keep us from being preempted
A> > + * during the critical sequences with the hardware.
A> > + *
A> > + * Note: this doesn't prevent multiple threads from putting the chips into
A> > + * config mode, but since we only do that to detect the type at startup the
A> > + * extra overhead isn't needed since Giant protects us from multiple entry
A> > + * and no other code changes these registers.
A> > + */
A> > +#define PPC_CONFIG_LOCK(ppc)		critical_enter()
A> > +#define PPC_CONFIG_UNLOCK(ppc)		critical_leave()
A> > +
A> 
A> s/critical_leave/critical_exit/?

Already fixed.

However, question to Warner.

Since code already executes under Giant, what is the reason for critical_section?
What's the problem if couple of outb instructions are split (assuming they are
properly serialized) across two CPUs?

-- 
Totus tuus, Glebius.