parisc: Fix argument pointer in real64_call_asm()

commit 6e3220ba33 upstream.

Fix the argument pointer (ap) to point to real-mode memory
instead of virtual memory.

It's interesting that this issue hasn't shown up earlier, as this could
have happened with any 64-bit PDC ROM code.

I just noticed it because I suddenly faced a HPMC while trying to execute
the 64-bit STI ROM code of an Visualize-FXe graphics card for the STI
text console.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/parisc/kernel/real2.S

@@ -248,9 +248,6 @@ ENTRY_CFI(real64_call_asm)
 	/* save fn */
 	copy	%arg2, %r31
 
-	/* set up the new ap */
-	ldo	64(%arg1), %r29
-
 	/* load up the arg registers from the saved arg area */
 	/* 32-bit calling convention passes first 4 args in registers */
 	ldd	0*REG_SZ(%arg1), %arg0		/* note overwriting arg0 */
@@ -262,7 +259,9 @@ ENTRY_CFI(real64_call_asm)
 	ldd	7*REG_SZ(%arg1), %r19
 	ldd	1*REG_SZ(%arg1), %arg1		/* do this one last! */
 
+	/* set up real-mode stack and real-mode ap */
 	tophys_r1 %sp
+	ldo	-16(%sp), %r29			/* Reference param save area */
 
 	b,l	rfi_virt2real,%r2
 	nop