imx8: add work in progress i.MX8MQ kernel for the mntreform2 laptop

This is a work in progress port to the mntreform2 laptop.

Working so far:

- mmu (same as raspberry pi 3b+)
- arm generic timer
- gicv3
- uart1
- enet

With access to the uart, one can netboot this kernel in u-boot
using the following commands:

> dhcp
> bootm

1 files changed, 58 insertions, 0 deletions

diff --git a/sys/src/9/imx8/sysreg.c b/sys/src/9/imx8/sysreg.c
new file mode 100644
index 000000000..1d892504e
--- /dev/null
+++ b/sys/src/9/imx8/sysreg.c
@@ -0,0 +1,58 @@
+/*
+ * ARMv8 system registers
+ * mainly to cope with arm hard-wiring register numbers into instructions.
+ *
+ * these routines must be callable from KZERO.
+ *
+ * on a multiprocessor, process switching to another cpu is assumed
+ * to be inhibited by the caller as these registers are local to the cpu.
+ */
+#include "u.h"
+#include "../port/lib.h"
+#include "mem.h"
+#include "dat.h"
+#include "fns.h"
+
+static void*
+mkinstr(ulong wd)
+{
+	static ulong ib[256], *ep[MAXMACH+1];
+	static Lock lk;
+	ulong *ip, *ie;
+
+	ie = ep[m->machno];
+	for(ip = ib; ip < ie; ip += 2)
+		if(*ip == wd)
+			return ip;
+
+	ilock(&lk);
+	ie = ep[MAXMACH];
+	for(; ip < ie; ip += 2)
+		if(*ip == wd)
+			goto Found;
+	if(ip >= &ib[nelem(ib)])
+		panic("mkinstr: out of instrucuction buffer");
+	ip[0] = wd;
+	ip[1] = 0xd65f03c0;	// RETURN
+	ep[MAXMACH] = ie = ip + 2;
+	cachedwbinvse(ip, 2*sizeof(*ip));
+Found:
+	iunlock(&lk);
+	cacheiinv();
+	ep[m->machno] = ie;
+	return ip;
+}
+
+uvlong
+sysrd(ulong spr)
+{
+	uvlong (*fp)(void) = mkinstr(0xd5380000UL | spr);
+	return fp();
+}
+
+void
+syswr(ulong spr, uvlong val)
+{
+	void (*fp)(uvlong) = mkinstr(0xd5180000UL | spr);
+	fp(val);
+}