parisc: Add runtime check to prevent PA2.0 kernels on PA1.x machines

If a 32-bit kernel was compiled for PA2.0 CPUs, it won't be able to run
on machines with PA1.x CPUs. Add a check and bail out early if a PA1.x
machine is detected.
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/kernel/head.S

@@ -22,7 +22,7 @@
 #include <linux/init.h>
 #include <linux/pgtable.h>
 
-	.level	PA_ASM_LEVEL
+	.level	1.1
 
 	__INITDATA
 ENTRY(boot_args)
@@ -70,6 +70,47 @@ $bss_loop:
 	stw,ma          %arg2,4(%r1)
 	stw,ma          %arg3,4(%r1)
 
+#if !defined(CONFIG_64BIT) && defined(CONFIG_PA20)
+	/* This 32-bit kernel was compiled for PA2.0 CPUs. Check current CPU
+	 * and halt kernel if we detect a PA1.x CPU. */
+	ldi		32,%r10
+	mtctl		%r10,%cr11
+	.level 2.0
+	mfctl,w		%cr11,%r10
+	.level 1.1
+	comib,<>,n	0,%r10,$cpu_ok
+
+	load32		PA(msg1),%arg0
+	ldi		msg1_end-msg1,%arg1
+$iodc_panic:
+	copy		%arg0, %r10
+	copy		%arg1, %r11
+	load32		PA(init_stack),%sp
+#define MEM_CONS 0x3A0
+	ldw		MEM_CONS+32(%r0),%arg0	// HPA
+	ldi		ENTRY_IO_COUT,%arg1
+	ldw		MEM_CONS+36(%r0),%arg2	// SPA
+	ldw		MEM_CONS+8(%r0),%arg3	// layers
+	load32		PA(__bss_start),%r1
+	stw		%r1,-52(%sp)		// arg4
+	stw		%r0,-56(%sp)		// arg5
+	stw		%r10,-60(%sp)		// arg6 = ptr to text
+	stw		%r11,-64(%sp)		// arg7 = len
+	stw		%r0,-68(%sp)		// arg8
+	load32		PA(.iodc_panic_ret), %rp
+	ldw		MEM_CONS+40(%r0),%r1	// ENTRY_IODC
+	bv,n		(%r1)
+.iodc_panic_ret:
+	b .				/* wait endless with ... */
+	or		%r10,%r10,%r10	/* qemu idle sleep */
+msg1:	.ascii "Can't boot kernel which was built for PA8x00 CPUs on this machine.\r\n"
+msg1_end:
+
+$cpu_ok:
+#endif
+
+	.level	PA_ASM_LEVEL
+
 	/* Initialize startup VM. Just map first 16/32 MB of memory */
 	load32		PA(swapper_pg_dir),%r4
 	mtctl		%r4,%cr24	/* Initialize kernel root pointer */