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misc: ioc4: simplify wave period measurement in clock_calibrate

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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>
This commit is contained in:
Richard Leitner 2014-12-08 16:28:10 +01:00 committed by Greg Kroah-Hartman
parent 0ec0cf1920
commit 769105aa74
1 changed files with 16 additions and 15 deletions
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31
drivers/misc/ioc4.c
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@ -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: