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 <d...@g0hl1n.net>
---
A simplification of this loop was suggested by Andrew Morton [1].
This is my first proposal of such a simplification.
Furthermore I'm not sure if the commit message is sufficient.
Please give me also some feedback on it.
If this simplification is not needed only initializing start to
ktime_get_ns() would fix the compiler warning too.
[1] https://lkml.org/lkml/2014/12/5/76
---
drivers/misc/ioc4.c | 31 ++++++++++++++++---------------
1 file changed, 16 insertions(+), 15 deletions(-)
diff --git a/drivers/misc/ioc4.c b/drivers/misc/ioc4.c
index 3336ddc..8758d03 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:
--
2.1.3
--
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