bcm: fix mysterious core clock resets under SMP (thanks richard miller)

reference: https://github.com/raspberrypi/firmware/issues/542

procsave(Proc* p)
{
	uvlong t;

	cycles(&t);
	p->pcycles += t;

// TODO: save and restore VFPv3 FP state once 5[cal] know the new registers.
	fpuprocsave(p);
	/*
	 * Prevent the following scenario:
	 *	pX sleeps on cpuA, leaving its page tables in mmul1
	 *	pX wakes up on cpuB, and exits, freeing its page tables
	 *  pY on cpuB allocates a freed page table page and overwrites with data
	 *  cpuA takes an interrupt, and is now running with bad page tables
	 * In theory this shouldn't hurt because only user address space tables
	 * are affected, and mmuswitch will clear mmul1 before a user process is
	 * dispatched.  But empirically it correlates with weird problems, eg
	 * resetting of the core clock at 0x4000001C which confuses local timers.
	 */
	if(conf.nmach > 1)
		mmuswitch(nil);
}

sys/src/9/bcm/arch.c

@@ -1 +1,203 @@
-#include "../omap/arch.c"
+#include "u.h"
+#include "../port/lib.h"
+#include "mem.h"
+#include "dat.h"
+#include "fns.h"
+#include "../port/error.h"
+
+#include <tos.h>
+#include "ureg.h"
+
+#include "arm.h"
+
+/*
+ * A lot of this stuff doesn't belong here
+ * but this is a convenient dumping ground for
+ * later sorting into the appropriate buckets.
+ */
+
+/* Give enough context in the ureg to produce a kernel stack for
+ * a sleeping process
+ */
+void
+setkernur(Ureg* ureg, Proc* p)
+{
+	ureg->pc = p->sched.pc;
+	ureg->sp = p->sched.sp+4;
+	ureg->r14 = PTR2UINT(sched);
+}
+
+/*
+ * called in sysfile.c
+ */
+void
+evenaddr(uintptr addr)
+{
+	if(addr & 3){
+		postnote(up, 1, "sys: odd address", NDebug);
+		error(Ebadarg);
+	}
+}
+
+/* go to user space */
+void
+kexit(Ureg*)
+{
+	uvlong t;
+	Tos *tos;
+
+	/* precise time accounting, kernel exit */
+	tos = (Tos*)(USTKTOP-sizeof(Tos));
+	cycles(&t);
+	tos->kcycles += t - up->kentry;
+	tos->pcycles = t + up->pcycles;
+	tos->cyclefreq = m->cpuhz;
+	tos->pid = up->pid;
+
+	/* make visible immediately to user proc */
+	cachedwbinvse(tos, sizeof *tos);
+}
+
+/*
+ *  return the userpc the last exception happened at
+ */
+uintptr
+userpc(void)
+{
+	Ureg *ureg = up->dbgreg;
+	return ureg->pc;
+}
+
+/* This routine must save the values of registers the user is not permitted
+ * to write from devproc and then restore the saved values before returning.
+ */
+void
+setregisters(Ureg* ureg, char* pureg, char* uva, int n)
+{
+	USED(ureg, pureg, uva, n);
+}
+
+/*
+ *  this is the body for all kproc's
+ */
+static void
+linkproc(void)
+{
+	spllo();
+	up->kpfun(up->kparg);
+	pexit("kproc exiting", 0);
+}
+
+/*
+ *  setup stack and initial PC for a new kernel proc.  This is architecture
+ *  dependent because of the starting stack location
+ */
+void
+kprocchild(Proc *p, void (*func)(void*), void *arg)
+{
+	p->sched.pc = PTR2UINT(linkproc);
+	p->sched.sp = PTR2UINT(p->kstack+KSTACK);
+
+	p->kpfun = func;
+	p->kparg = arg;
+}
+
+/*
+ *  pc output by dumpaproc
+ */
+uintptr
+dbgpc(Proc* p)
+{
+	Ureg *ureg;
+
+	ureg = p->dbgreg;
+	if(ureg == 0)
+		return 0;
+
+	return ureg->pc;
+}
+
+/*
+ *  set mach dependent process state for a new process
+ */
+void
+procsetup(Proc* p)
+{
+	fpusysprocsetup(p);
+
+	cycles(&p->kentry);
+	p->pcycles = -p->kentry;
+}
+
+void
+procfork(Proc* p)
+{
+	p->kentry = up->kentry;
+	p->pcycles = -p->kentry;
+
+	fpuprocfork(p);
+}
+
+/*
+ *  Save the mach dependent part of the process state.
+ */
+void
+procsave(Proc* p)
+{
+	uvlong t;
+
+	cycles(&t);
+	p->pcycles += t;
+	p->kentry -= t;
+
+// TODO: save and restore VFPv3 FP state once 5[cal] know the new registers.
+	fpuprocsave(p);
+
+	/*
+	 * Prevent the following scenario:
+	 *	pX sleeps on cpuA, leaving its page tables in mmul1
+	 *	pX wakes up on cpuB, and exits, freeing its page tables
+	 *  pY on cpuB allocates a freed page table page and overwrites with data
+	 *  cpuA takes an interrupt, and is now running with bad page tables
+	 * In theory this shouldn't hurt because only user address space tables
+	 * are affected, and mmuswitch will clear mmul1 before a user process is
+	 * dispatched.  But empirically it correlates with weird problems, eg
+	 * resetting of the core clock at 0x4000001C which confuses local timers.
+	 */
+	if(conf.nmach > 1)
+		mmuswitch(nil);
+}
+
+void
+procrestore(Proc* p)
+{
+	uvlong t;
+
+	if(p->kp)
+		return;
+	cycles(&t);
+	p->pcycles -= t;
+	p->kentry += t;
+
+	fpuprocrestore(p);
+}
+
+int
+userureg(Ureg* ureg)
+{
+	return (ureg->psr & PsrMask) == PsrMusr;
+}
+
+int
+cas32(void* addr, u32int old, u32int new)
+{
+	int r, s;
+
+	s = splhi();
+	if(r = (*(u32int*)addr == old))
+		*(u32int*)addr = new;
+	splx(s);
+	if (r)
+		coherence();
+	return r;
+}