Commit 2db4bc34 authored Apr 01, 2014 by Maciej W. Rozycki Committed by Ralf Baechle May 13, 2014

MIPS: __delay CPU_DADDI_WORKAROUNDS bug fix



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@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6669/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

parent 824122a3

arch/mips/lib/delay.c

+10 −4

Original line number	Diff line number	Diff line
		@@ -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);

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