cuda: factor out timebase-derived counter value and load time

Commit b981289c "PPC: Cuda: Use cuda timer to expose tbfreq to guest" altered
the timer calculations from those based upon the hardware CUDA clock frequency
to those based upon the CPU timebase frequency.

In fact we can isolate the differences to 2 simple changes: one to the counter
read value and another to the counter load time. Move these changes into
separate functions so the implementation can be swapped later.
Signed-off-by: NMark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

hw/misc/macio/cuda.c

@@ -145,21 +145,29 @@ static void cuda_update_irq(CUDAState *s)
     }
 }
 
-static uint64_t get_tb(uint64_t time, uint64_t freq)
+static uint64_t get_counter_value(CUDAState *s, CUDATimer *ti)
 {
-    return muldiv64(time, freq, NANOSECONDS_PER_SECOND);
+    /* Reverse of the tb calculation algorithm that Mac OS X uses on bootup */
+    uint64_t tb_diff = muldiv64(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL),
+                                s->tb_frequency, NANOSECONDS_PER_SECOND) -
+                           ti->load_time;
+
+    return (tb_diff * 0xBF401675E5DULL) / (s->tb_frequency << 24);
+}
+
+static uint64_t get_counter_load_time(CUDAState *s, CUDATimer *ti)
+{
+    uint64_t load_time = muldiv64(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL),
+                                  s->tb_frequency, NANOSECONDS_PER_SECOND);
+    return load_time;
 }
 
 static unsigned int get_counter(CUDAState *s, CUDATimer *ti)
 {
     int64_t d;
     unsigned int counter;
-    uint64_t tb_diff;
-    uint64_t current_time = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 
-    /* Reverse of the tb calculation algorithm that Mac OS X uses on bootup. */
-    tb_diff = get_tb(current_time, s->tb_frequency) - ti->load_time;
-    d = (tb_diff * 0xBF401675E5DULL) / (s->tb_frequency << 24);
+    d = get_counter_value(s, ti);
 
     if (ti->index == 0) {
         /* the timer goes down from latch to -1 (period of latch + 2) */
@@ -178,8 +186,7 @@ static unsigned int get_counter(CUDAState *s, CUDATimer *ti)
 static void set_counter(CUDAState *s, CUDATimer *ti, unsigned int val)
 {
     CUDA_DPRINTF("T%d.counter=%d\n", 1 + ti->index, val);
-    ti->load_time = get_tb(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL),
-                           s->tb_frequency);
+    ti->load_time = get_counter_load_time(s, ti);
     ti->counter_value = val;
     cuda_timer_update(s, ti, ti->load_time);
 }