MIPS: store the appended dtb address in a variable

Instead of rewriting the arguments to match the UHI spec, store the
address of a appended or UHI supplied dtb in fw_supplied_dtb.

That way the original bootloader arugments are kept intact while still
making the use of an appended dtb invisible for mach code.

Mach code can still find out if it is an appended dtb by comparing
fw_arg1 with fw_supplied_dtb.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Cc: Kevin Cernekee <cernekee@gmail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: John Crispin <john@phrozen.org>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Alban Bedel <albeu@free.fr>
Cc: Daniel Gimpelevich <daniel@gimpelevich.san-francisco.ca.us>
Cc: Antony Pavlov <antonynpavlov@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13699/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/head.S

@@ -93,21 +93,24 @@ NESTED(kernel_entry, 16, sp)			# kernel entry point
 	jr	t0
 0:
 
+#ifdef CONFIG_USE_OF
 #ifdef CONFIG_MIPS_RAW_APPENDED_DTB
-	PTR_LA		t0, __appended_dtb
+	PTR_LA		t2, __appended_dtb
 
 #ifdef CONFIG_CPU_BIG_ENDIAN
 	li		t1, 0xd00dfeed
 #else
 	li		t1, 0xedfe0dd0
 #endif
-	lw		t2, (t0)
-	bne		t1, t2, not_found
-	 nop
+	lw		t0, (t2)
+	beq		t0, t1, dtb_found
+#endif
+	li		t1, -2
+	beq		a0, t1, dtb_found
+	move		t2, a1
 
-	move		a1, t0
-	PTR_LI		a0, -2
-not_found:
+	li		t2, 0
+dtb_found:
 #endif
 	PTR_LA		t0, __bss_start		# clear .bss
 	LONG_S		zero, (t0)
@@ -122,6 +125,10 @@ not_found:
 	LONG_S		a2, fw_arg2
 	LONG_S		a3, fw_arg3
 
+#ifdef CONFIG_USE_OF
+	LONG_S		t2, fw_passed_dtb
+#endif
+
 	MTC0		zero, CP0_CONTEXT	# clear context register
 	PTR_LA		$28, init_thread_union
 	/* Set the SP after an empty pt_regs.  */