misc: ioc4: simplify wave period measurement in clock_calibrate

The loop for measuring the square wave periods over some cycles is
refactored to be more easily readable. This includes avoiding a
"by-hand-implemented" for loop with a "real" one and adding some
comments.

Furthermore the following compiler warning is avoided by this patch:
drivers/misc/ioc4.c: In function ‘ioc4_probe’:
drivers/misc/ioc4.c:194:16: warning: ‘start’ may be used uninitialized
in this function [-Wmaybe-uninitialized]
  period = (end - start) /
                ^
drivers/misc/ioc4.c:148:11: note: ‘start’ was declared here
  uint64_t start, end, period;
           ^

Signed-off-by: Richard Leitner <dev@g0hl1n.net>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 16 insertions, 15 deletions

diff --git a/drivers/misc/ioc4.c b/drivers/misc/ioc4.c
index 3336ddca45ac..8758d033db23 100644
--- a/drivers/misc/ioc4.c
+++ b/drivers/misc/ioc4.c
@@ -144,9 +144,9 @@ ioc4_clock_calibrate(struct ioc4_driver_data *idd)
 {
         union ioc4_int_out int_out;
         union ioc4_gpcr gpcr;
-        unsigned int state, last_state = 1;
+        unsigned int state, last_state;
         uint64_t start, end, period;
-        unsigned int count = 0;
+        unsigned int count;
 
         /* Enable output */
         gpcr.raw = 0;
@@ -167,19 +167,20 @@ ioc4_clock_calibrate(struct ioc4_driver_data *idd)
         mmiowb();
 
         /* Check square wave period averaged over some number of cycles */
-        do {
-                int_out.raw = readl(&idd->idd_misc_regs->int_out.raw);
-                state = int_out.fields.int_out;
-                if (!last_state && state) {
-                        count++;
-                        if (count == IOC4_CALIBRATE_END) {
-                                end = ktime_get_ns();
-                                break;
-                        } else if (count == IOC4_CALIBRATE_DISCARD)
-                                start = ktime_get_ns();
-                }
-                last_state = state;
-        } while (1);
+        start = ktime_get_ns();
+        state = 1; /* make sure the first read isn't a rising edge */
+        for (count = 0; count <= IOC4_CALIBRATE_END; count++) {
+                do { /* wait for a rising edge */
+                        last_state = state;
+                        int_out.raw = readl(&idd->idd_misc_regs->int_out.raw);
+                        state = int_out.fields.int_out;
+                } while (last_state || !state);
+
+                /* discard the first few cycles */
+                if (count == IOC4_CALIBRATE_DISCARD)
+                        start = ktime_get_ns();
+        }
+        end = ktime_get_ns();
 
         /* Calculation rearranged to preserve intermediate precision.
          * Logically: