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>

diff --git a/drivers/misc/ioc4.c b/drivers/misc/ioc4.c
index 3336ddc..8758d03 100644 (file)
--- 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: