With CPU_DADDI_WORKAROUNDS enabled __delay assembles with a macro in a
branch delay slot:
{standard input}: Assembler messages:
{standard input}:18: Warning: Macro instruction expanded into multiple
instructions in a branch delay slot
and broken code results:
0000000000000000 <__delay>:
0: 1480ffff bnez a0,0 <__delay>
4: 24010001 li at,1
8: 0081202f dsubu a0,a0,at
c: 03e00008 jr ra
10: 00000000 nop
14: 00000000 nop
Consequently the function loops indefinitely, showing up prominently as a
hang in the delay loop calibration at bootstrap.
This change corrects the problem by forcing the immediate 1 into a
register while keeping code produced identical where CPU_DADDI_WORKAROUNDS
is disabled.
Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxxxxx>
---
linux-mips-delay-nodaddi-fix.patch
Index: linux-20140329-4maxp64/arch/mips/lib/delay.c
===================================================================
--- linux-20140329-4maxp64.orig/arch/mips/lib/delay.c
+++ linux-20140329-4maxp64/arch/mips/lib/delay.c
@@ -6,7 +6,7 @@
* Copyright (C) 1994 by Waldorf Electronics
* Copyright (C) 1995 - 2000, 01, 03 by Ralf Baechle
* Copyright (C) 1999, 2000 Silicon Graphics, Inc.
- * Copyright (C) 2007 Maciej W. Rozycki
+ * Copyright (C) 2007, 2014 Maciej W. Rozycki
*/
#include <linux/module.h>
#include <linux/param.h>
@@ -15,6 +15,12 @@
#include <asm/compiler.h>
#include <asm/war.h>
+#ifndef CONFIG_CPU_DADDI_WORKAROUNDS
+#define GCC_DADDI_IMM_ASM() "I"
+#else
+#define GCC_DADDI_IMM_ASM() "r"
+#endif
+
void __delay(unsigned long loops)
{
__asm__ __volatile__ (
@@ -22,13 +28,13 @@ void __delay(unsigned long loops)
" .align 3 \n"
"1: bnez %0, 1b \n"
#if BITS_PER_LONG == 32
- " subu %0, 1 \n"
+ " subu %0, %1 \n"
#else
- " dsubu %0, 1 \n"
+ " dsubu %0, %1 \n"
#endif
" .set reorder \n"
: "=r" (loops)
- : "0" (loops));
+ : GCC_DADDI_IMM_ASM() (1), "0" (loops));
}
EXPORT_SYMBOL(__delay);
