[PATCH] ioc4: silence GCC warning

[Paul Bolle]

Building ioc4.o triggers a GCC warning since v3.17-rc1:
    drivers/misc/ioc4.c: In function âioc4_probeâ:
    drivers/misc/ioc4.c:194:16: warning: âstartâ may be used uninitialized in this function [-Wmaybe-uninitialized]
      period = (end - start) /
                    ^
    drivers/misc/ioc4.c:148:11: note: âstartâ was declared here
      uint64_t start, end, period;
               ^

This is a false positive. Apparently the recent change to use
ktime_get_ns() makes it harder for GCC to analyze the codeflow.

Adding a small (inline) function that only returns after a certain
number of wave cycles have been seen allows to reorder the code a bit.
And after reordering it is clearer for both the compiler and the human
reader what's going on here. So let's do that.

Not-yet-signed-off-by: Paul Bolle <pebolle@xxxxxxxxxx>
---
 drivers/misc/ioc4.c | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/drivers/misc/ioc4.c b/drivers/misc/ioc4.c
index 3336ddca45ac..e8209fa78713 100644
--- a/drivers/misc/ioc4.c
+++ b/drivers/misc/ioc4.c
@@ -122,11 +122,25 @@ ioc4_unregister_submodule(struct ioc4_submodule *is)
 #define IOC4_CALIBRATE_DEFAULT \
 	(1000*IOC4_EXTINT_COUNT_DIVISOR/IOC4_CALIBRATE_DEFAULT_MHZ)
 
-#define IOC4_CALIBRATE_END \
-	(IOC4_CALIBRATE_CYCLES + IOC4_CALIBRATE_DISCARD)
-
 #define IOC4_INT_OUT_MODE_TOGGLE 0x7	/* Toggle INT_OUT every COUNT+1 ticks */
 
+/* return after count wave cycles have been seen */
+static inline void
+ioc4_clock_wave_cycles(struct ioc4_driver_data *idd, unsigned int count)
+{
+	union ioc4_int_out int_out;
+	unsigned int state, last_state = 1;
+	unsigned int i = 0;
+
+	do {
+		int_out.raw = readl(&idd->idd_misc_regs->int_out.raw);
+		state = int_out.fields.int_out;
+		if (!last_state && state)
+			i++;
+		last_state = state;
+	} while (i < count);
+}
+
 /* Determines external interrupt output clock period of the PCI bus an
  * IOC4 is attached to.  This value can be used to determine the PCI
  * bus speed.
@@ -144,9 +158,7 @@ ioc4_clock_calibrate(struct ioc4_driver_data *idd)
 {
 	union ioc4_int_out int_out;
 	union ioc4_gpcr gpcr;
-	unsigned int state, last_state = 1;
 	uint64_t start, end, period;
-	unsigned int count = 0;
 
 	/* Enable output */
 	gpcr.raw = 0;
@@ -167,19 +179,10 @@ 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);
+	ioc4_clock_wave_cycles(idd, IOC4_CALIBRATE_DISCARD);
+	start = ktime_get_ns();
+	ioc4_clock_wave_cycles(idd, IOC4_CALIBRATE_COUNT);
+	end = ktime_get_ns();
 
 	/* Calculation rearranged to preserve intermediate precision.
 	 * Logically:
-- 
1.9.3


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