PERFORCE change 125328 for review

[Constantine A. Murenin]

http://perforce.freebsd.org/chv.cgi?CH=125328

Change 125328 by cnst at dale on 2007/08/19 02:45:16

	make coretemp_get_temp() more robust in preparation for a patch
	converting coretemp(4) to sysctl(3) hw.sensors framework. 
	
	If coretemp_get_temp() is called before smp is started, then it
	will generate a panic around sched_bind (at least on sched_4bsd).
	(This is what will happen if we try to load coretemp at boot time,
	and then shortly thereafter call coretemp_get_temp() from, for 
	example, sensor_task thread.)
	
	To account for this, we are now going to check that the number
	of initialised processors is greater than 1, and return -1 if
	someone tries to read a temperature from an uninitialised CPU.
	
	Special thanks go to rpaulo@ for discussing this issue with me
	on IRC, and pointing me at smp_cpus.
	
	rpaulo suggested that I include <sys/smp.h>, and use #ifdef SMP
	around smp_cpus, but it turns out that:
	1. when we compile coretemp(4) as a module, SMP is not defined
	2. in <sys/smp.h>, smp_cpus is only extern'ed if SMP is defined
	3. smp_cpus is declared regardless of SMP define in kern/subr_smp.c
	
	Thus a better solution is to use `extern int smp_cpus` at this time,
	although a fix for <sys/smp.h> might be better in the long-term.
	
	Discussed with rpaulo@, thanks also go to Nick Barkas of moduli.net
	for running publicly accessible OpenGrok service for FreeBSD. :)

Affected files ...

.. //depot/projects/soc2007/cnst-sensors/sys.dev.coretemp/coretemp.c#3 edit

Differences ...

==== //depot/projects/soc2007/cnst-sensors/sys.dev.coretemp/coretemp.c#3 (text+ko) ====

@@ -50,6 +50,8 @@
 #include <machine/cpufunc.h>
 #include <machine/md_var.h>
 
+extern int smp_cpus;
+
 struct coretemp_softc {
 	device_t	sc_dev;
 	int		sc_tjmax;
@@ -208,9 +210,17 @@
 	int cpu = device_get_unit(dev);
 	struct coretemp_softc *sc = device_get_softc(dev);
 
-	thread_lock(curthread);
-	sched_bind(curthread, cpu);
-	thread_unlock(curthread);
+	/*
+	 * Bind to specific CPU to read the correct temperature.
+	 * If not all CPUs are initialised, then only read from
+	 * cpu0, returning -1 on all other CPUs.
+	 */
+	if (smp_cpus > 1) {
+		thread_lock(curthread);
+		sched_bind(curthread, cpu);
+		thread_unlock(curthread);
+	} else if (cpu != 0)
+		return (-1);
 
 	/*
 	 * The digital temperature reading is located at bit 16