ARM: 7452/1: delay: allow timer-based delay implementation to be selected

This patch allows a timer-based delay implementation to be selected by
switching the delay routines over to use get_cycles, which is
implemented in terms of read_current_timer. This further allows us to
skip the loop calibration and have a consistent delay function in the
face of core frequency scaling.

To avoid the pain of dealing with memory-mapped counters, this
implementation uses the co-processor interface to the architected timers
when they are available. The previous loop-based implementation is
kept around for CPUs without the architected timers and we retain both
the maximum delay (2ms) and the corresponding conversion factors for
determining the number of loops required for a given interval. Since the
indirection of the timer routines will only work when called from C,
the sa1100 sleep routines are modified to branch to the loop-based delay
functions directly.

Tested-by: Shinya Kuribayashi <shinya.kuribayashi.px@renesas.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

7 files changed, 114 insertions, 25 deletions

diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h
index b2deda181549..dc6145120de3 100644
--- a/arch/arm/include/asm/delay.h
+++ b/arch/arm/include/asm/delay.h
@@ -6,9 +6,22 @@
 #ifndef __ASM_ARM_DELAY_H
 #define __ASM_ARM_DELAY_H
 
+#include <asm/memory.h>
 #include <asm/param.h>  /* HZ */
 
-extern void __delay(int loops);
+#define MAX_UDELAY_MS   2
+#define UDELAY_MULT     ((UL(2199023) * HZ) >> 11)
+#define UDELAY_SHIFT    30
+
+#ifndef __ASSEMBLY__
+
+extern struct arm_delay_ops {
+        void (*delay)(unsigned long);
+        void (*const_udelay)(unsigned long);
+        void (*udelay)(unsigned long);
+} arm_delay_ops;
+
+#define __delay(n)              arm_delay_ops.delay(n)
 
 /*
  * This function intentionally does not exist; if you see references to
@@ -23,22 +36,27 @@ extern void __bad_udelay(void);
  * division by multiplication: you don't have to worry about
  * loss of precision.
  *
- * Use only for very small delays ( < 1 msec).  Should probably use a
+ * Use only for very small delays ( < 2 msec).  Should probably use a
  * lookup table, really, as the multiplications take much too long with
  * short delays.  This is a "reasonable" implementation, though (and the
  * first constant multiplications gets optimized away if the delay is
  * a constant)
  */
-extern void __udelay(unsigned long usecs);
-extern void __const_udelay(unsigned long);
-
-#define MAX_UDELAY_MS 2
+#define __udelay(n)             arm_delay_ops.udelay(n)
+#define __const_udelay(n)       arm_delay_ops.const_udelay(n)
 
 #define udelay(n)                                                       \
         (__builtin_constant_p(n) ?                                      \
           ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :              \
-                        __const_udelay((n) * ((2199023U*HZ)>>11))) :    \
+                        __const_udelay((n) * UDELAY_MULT)) :            \
           __udelay(n))
 
+/* Loop-based definitions for assembly code. */
+extern void __loop_delay(unsigned long loops);
+extern void __loop_udelay(unsigned long usecs);
+extern void __loop_const_udelay(unsigned long);
+
+#endif /* __ASSEMBLY__ */
+
 #endif /* defined(_ARM_DELAY_H) */
 
diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c
index dbbeec4f06e2..675cee09c014 100644
--- a/arch/arm/kernel/arch_timer.c
+++ b/arch/arm/kernel/arch_timer.c
@@ -32,6 +32,8 @@ static int arch_timer_ppi2;
 
 static struct clock_event_device __percpu **arch_timer_evt;
 
+extern void init_current_timer_delay(unsigned long freq);
+
 /*
  * Architected system timer support.
  */
@@ -304,6 +306,7 @@ static int __init arch_timer_register(void)
         if (err)
                 goto out_free_irq;
 
+        init_current_timer_delay(arch_timer_rate);
         return 0;
 
 out_free_irq:
diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c
index b57c75e0b01f..71962284d288 100644
--- a/arch/arm/kernel/armksyms.c
+++ b/arch/arm/kernel/armksyms.c
@@ -49,8 +49,7 @@ extern void __aeabi_ulcmp(void);
 extern void fpundefinstr(void);
 
         /* platform dependent support */
-EXPORT_SYMBOL(__udelay);
-EXPORT_SYMBOL(__const_udelay);
+EXPORT_SYMBOL(arm_delay_ops);
 
         /* networking */
 EXPORT_SYMBOL(csum_partial);
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 992769ae2599..b621114644fd 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -6,7 +6,7 @@
 
 lib-y           := backtrace.o changebit.o csumipv6.o csumpartial.o   \
                    csumpartialcopy.o csumpartialcopyuser.o clearbit.o \
-                   delay.o findbit.o memchr.o memcpy.o                \
+                   delay.o delay-loop.o findbit.o memchr.o memcpy.o   \
                    memmove.o memset.o memzero.o setbit.o              \
                    strncpy_from_user.o strnlen_user.o                 \
                    strchr.o strrchr.o                                 \
diff --git a/arch/arm/lib/delay.S b/arch/arm/lib/delay-loop.S
index 3c9a05c8d20b..36b668d8e121 100644
--- a/arch/arm/lib/delay.S
+++ b/arch/arm/lib/delay-loop.S
@@ -9,11 +9,11 @@
  */
 #include <linux/linkage.h>
 #include <asm/assembler.h>
-#include <asm/param.h>
+#include <asm/delay.h>
                 .text
 
 .LC0:           .word   loops_per_jiffy
-.LC1:           .word   (2199023*HZ)>>11
+.LC1:           .word   UDELAY_MULT
 
 /*
  * r0  <= 2000
@@ -21,10 +21,10 @@
  * HZ  <= 1000
  */
 
-ENTRY(__udelay)
+ENTRY(__loop_udelay)
                 ldr     r2, .LC1
                 mul     r0, r2, r0
-ENTRY(__const_udelay)                           @ 0 <= r0 <= 0x7fffff06
+ENTRY(__loop_const_udelay)                      @ 0 <= r0 <= 0x7fffff06
                 mov     r1, #-1
                 ldr     r2, .LC0
                 ldr     r2, [r2]                @ max = 0x01ffffff
@@ -39,12 +39,10 @@ ENTRY(__const_udelay)				@ 0 <= r0 <= 0x7fffff06
 
 /*
  * loops = r0 * HZ * loops_per_jiffy / 1000000
- *
- * Oh, if only we had a cycle counter...
  */
 
 @ Delay routine
-ENTRY(__delay)
+ENTRY(__loop_delay)
                 subs    r0, r0, #1
 #if 0
                 movls   pc, lr
@@ -62,8 +60,8 @@ ENTRY(__delay)
                 movls   pc, lr
                 subs    r0, r0, #1
 #endif
-                bhi     __delay
+                bhi     __loop_delay
                 mov     pc, lr
-ENDPROC(__udelay)
-ENDPROC(__const_udelay)
-ENDPROC(__delay)
+ENDPROC(__loop_udelay)
+ENDPROC(__loop_const_udelay)
+ENDPROC(__loop_delay)
diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c
new file mode 100644
index 000000000000..d6dacc69254e
--- /dev/null
+++ b/arch/arm/lib/delay.c
@@ -0,0 +1,71 @@
+/*
+ * Delay loops based on the OpenRISC implementation.
+ *
+ * Copyright (C) 2012 ARM Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *
+ * Author: Will Deacon <will.deacon@arm.com>
+ */
+
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/timex.h>
+
+/*
+ * Default to the loop-based delay implementation.
+ */
+struct arm_delay_ops arm_delay_ops = {
+        .delay          = __loop_delay,
+        .const_udelay   = __loop_const_udelay,
+        .udelay         = __loop_udelay,
+};
+
+#ifdef ARCH_HAS_READ_CURRENT_TIMER
+static void __timer_delay(unsigned long cycles)
+{
+        cycles_t start = get_cycles();
+
+        while ((get_cycles() - start) < cycles)
+                cpu_relax();
+}
+
+static void __timer_const_udelay(unsigned long xloops)
+{
+        unsigned long long loops = xloops;
+        loops *= loops_per_jiffy;
+        __timer_delay(loops >> UDELAY_SHIFT);
+}
+
+static void __timer_udelay(unsigned long usecs)
+{
+        __timer_const_udelay(usecs * UDELAY_MULT);
+}
+
+void __init init_current_timer_delay(unsigned long freq)
+{
+        pr_info("Switching to timer-based delay loop\n");
+        lpj_fine                        = freq / HZ;
+        arm_delay_ops.delay             = __timer_delay;
+        arm_delay_ops.const_udelay      = __timer_const_udelay;
+        arm_delay_ops.udelay            = __timer_udelay;
+}
+
+unsigned long __cpuinit calibrate_delay_is_known(void)
+{
+        return lpj_fine;
+}
+#endif
diff --git a/arch/arm/mach-sa1100/sleep.S b/arch/arm/mach-sa1100/sleep.S
index 30cc6721665b..85863741ef8b 100644
--- a/arch/arm/mach-sa1100/sleep.S
+++ b/arch/arm/mach-sa1100/sleep.S
@@ -38,9 +38,9 @@ ENTRY(sa1100_finish_suspend)
         orr     r4, r4, #MDREFR_K1DB2
         ldr     r5, =PPCR
 
-        @ Pre-load __udelay into the I-cache
+        @ Pre-load __loop_udelay into the I-cache
         mov     r0, #1
-        bl      __udelay
+        bl      __loop_udelay
         mov     r0, r0
 
         @ The following must all exist in a single cache line to
@@ -53,11 +53,11 @@ ENTRY(sa1100_finish_suspend)
         @ delay 90us and set CPU PLL to lowest speed
         @ fixes resume problem on high speed SA1110
         mov     r0, #90
-        bl      __udelay
+        bl      __loop_udelay
         mov     r1, #0
         str     r1, [r5]
         mov     r0, #90
-        bl      __udelay
+        bl      __loop_udelay
 
         /*
          * SA1110 SDRAM controller workaround.  register values: