Where we can, pass the kernel an FDT facsimile of the OF device tree rather

than a pointer to Open Firmware by default. This eliminates a number of
potentially unsafe calls to firmware from the kernel and provides better
performance.

This feature is meant to be expanded until it is on by default
unconditionally and, ideally, we can then garbage-collect the
nightmare pile of hacks required to call into Open Firmware from a live
kernel.

Reviewed by:	jhibbits

stand/powerpc/ofw/main.c

@@ -33,6 +33,8 @@ __FBSDID("$FreeBSD$");
 #include "libofw.h"
 #include "bootstrap.h"
 
+#include <machine/psl.h>
+
 struct arch_switch	archsw;		/* MI/MD interface boundary */
 
 extern char end[];
@@ -47,6 +49,16 @@ static char heap[HEAP_SIZE]; // In BSS, so uses no space
 
 #define OF_puts(fd, text) OF_write(fd, text, strlen(text))
 
+static __inline register_t
+mfmsr(void)
+{
+	register_t value;
+
+	__asm __volatile ("mfmsr %0" : "=r"(value));
+
+	return (value);
+}
+
 void
 init_heap(void)
 {
@@ -145,6 +157,15 @@ main(int (*openfirm)(void *))
 	    env_nounset);
 	setenv("LINES", "24", 1);		/* optional */
 
+	/*
+	 * On non-Apple hardware, where it works reliably, pass flattened
+	 * device trees to the kernel by default instead of OF CI pointers.
+	 * Apple hardware is the only virtual-mode OF implementation in
+	 * existence, so far as I am aware, so use that as a flag.
+	 */
+	if (!(mfmsr() & PSL_DR))
+		setenv("usefdt", "1", 1);
+
 	archsw.arch_getdev = ofw_getdev;
 	archsw.arch_copyin = ofw_copyin;
 	archsw.arch_copyout = ofw_copyout;