ARM: 7538/1: delay: add registration mechanism for delay timer sources

The current timer-based delay loop relies on the architected timer to
initiate the switch away from the polling-based implementation. This is
unfortunate for platforms without the architected timers but with a
suitable delay source (that is, constant frequency, always powered-up
and ticking as long as the CPUs are online).

This patch introduces a registration mechanism for the delay timer
(which provides an unconditional read_current_timer implementation) and
updates the architected timer code to use the new interface.

Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Jonathan Austin <jonathan.austin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 26 insertions, 8 deletions

diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c
index d6dacc69254e..9d0a30032d7f 100644
--- a/arch/arm/lib/delay.c
+++ b/arch/arm/lib/delay.c
@@ -34,7 +34,18 @@ struct arm_delay_ops arm_delay_ops = {
         .udelay         = __loop_udelay,
 };
 
-#ifdef ARCH_HAS_READ_CURRENT_TIMER
+static const struct delay_timer *delay_timer;
+static bool delay_calibrated;
+
+int read_current_timer(unsigned long *timer_val)
+{
+        if (!delay_timer)
+                return -ENXIO;
+
+        *timer_val = delay_timer->read_current_timer();
+        return 0;
+}
+
 static void __timer_delay(unsigned long cycles)
 {
         cycles_t start = get_cycles();
@@ -55,17 +66,24 @@ static void __timer_udelay(unsigned long usecs)
         __timer_const_udelay(usecs * UDELAY_MULT);
 }
 
-void __init init_current_timer_delay(unsigned long freq)
+void __init register_current_timer_delay(const struct delay_timer *timer)
 {
-        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;
+        if (!delay_calibrated) {
+                pr_info("Switching to timer-based delay loop\n");
+                delay_timer                     = timer;
+                lpj_fine                        = timer->freq / HZ;
+                loops_per_jiffy                 = lpj_fine;
+                arm_delay_ops.delay             = __timer_delay;
+                arm_delay_ops.const_udelay      = __timer_const_udelay;
+                arm_delay_ops.udelay            = __timer_udelay;
+                delay_calibrated                = true;
+        } else {
+                pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
+        }
 }
 
 unsigned long __cpuinit calibrate_delay_is_known(void)
 {
+        delay_calibrated = true;
         return lpj_fine;
 }
-#endif