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>

2 files changed, 4 insertions, 2 deletions

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);