Add a platform clocksource by adapting the existing arch_gettimeoffset
implementation.

Signed-off-by: Finn Thain <fth...@telegraphics.com.au>
Acked-by: Linus Walleij <linus.wall...@linaro.org>
---
Changed since v2:
 - Don't check for timer interrupt in amiga_read_clk() when the timer is
about to be reloaded.

Changed since v1:
 - Moved clk_total access to within the irq lock.
---
 arch/m68k/amiga/config.c | 64 +++++++++++++++++++++++++++-------------
 1 file changed, 43 insertions(+), 21 deletions(-)

diff --git a/arch/m68k/amiga/config.c b/arch/m68k/amiga/config.c
index d4976c1aa0cc..0c2c07318f6c 100644
--- a/arch/m68k/amiga/config.c
+++ b/arch/m68k/amiga/config.c
@@ -17,6 +17,7 @@
 #include <linux/mm.h>
 #include <linux/seq_file.h>
 #include <linux/tty.h>
+#include <linux/clocksource.h>
 #include <linux/console.h>
 #include <linux/rtc.h>
 #include <linux/init.h>
@@ -461,7 +462,28 @@ void __init config_amiga(void)
                *(unsigned char *)ZTWO_VADDR(0xde0002) |= 0x80;
 }
 
+static u64 amiga_read_clk(struct clocksource *cs);
+
+static struct clocksource amiga_clk = {
+       .name   = "ciab",
+       .rating = 250,
+       .read   = amiga_read_clk,
+       .mask   = CLOCKSOURCE_MASK(32),
+       .flags  = CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
 static unsigned short jiffy_ticks;
+static u32 clk_total;
+
+static irqreturn_t ciab_timer_handler(int irq, void *dev_id)
+{
+       irq_handler_t timer_routine = dev_id;
+
+       clk_total += jiffy_ticks;
+       timer_routine(0, NULL);
+
+       return IRQ_HANDLED;
+}
 
 static void __init amiga_sched_init(irq_handler_t timer_routine)
 {
@@ -481,41 +503,41 @@ static void __init amiga_sched_init(irq_handler_t 
timer_routine)
         * Please don't change this to use ciaa, as it interferes with the
         * SCSI code. We'll have to take a look at this later
         */
-       if (request_irq(IRQ_AMIGA_CIAB_TA, timer_routine, 0, "timer", NULL))
+       if (request_irq(IRQ_AMIGA_CIAB_TA, ciab_timer_handler, IRQF_TIMER,
+                       "timer", timer_routine))
                pr_err("Couldn't register timer interrupt\n");
        /* start timer */
        ciab.cra |= 0x11;
-}
 
-#define TICK_SIZE 10000
+       clocksource_register_hz(&amiga_clk, amiga_eclock);
+}
 
-/* This is always executed with interrupts disabled.  */
-static u32 amiga_gettimeoffset(void)
+static u64 amiga_read_clk(struct clocksource *cs)
 {
-       unsigned short hi, lo, hi2;
+       unsigned long flags;
+       u8 msb, lsb, tmp;
        u32 ticks, offset = 0;
 
-       /* read CIA B timer A current value */
-       hi  = ciab.tahi;
-       lo  = ciab.talo;
-       hi2 = ciab.tahi;
+       local_irq_save(flags);
 
-       if (hi != hi2) {
-               lo = ciab.talo;
-               hi = hi2;
-       }
-
-       ticks = hi << 8 | lo;
+       /* read CIA B timer A current value */
+       tmp = ciab.tahi;
+       lsb = ciab.talo;
+       msb = ciab.tahi;
+       if (msb != tmp)
+               lsb = ciab.talo;
 
-       if (ticks > jiffy_ticks / 2)
+       if (msb > 0)
                /* check for pending interrupt */
                if (cia_set_irq(&ciab_base, 0) & CIA_ICR_TA)
-                       offset = 10000;
+                       offset = jiffy_ticks;
+
+       ticks = jiffy_ticks - (msb << 8 | lsb);
+       ticks += offset + clk_total;
 
-       ticks = jiffy_ticks - ticks;
-       ticks = (10000 * ticks) / jiffy_ticks;
+       local_irq_restore(flags);
 
-       return (ticks + offset) * 1000;
+       return ticks;
 }
 
 static void amiga_reset(void)  __noreturn;
-- 
2.18.1

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