[RFC PATCH 1/1] lib: sbi_timer: Added a blocking wait function that waits until a certain condition is true or timeout occurs

[Adnan Rahman Chowdhury]

Motivation: Suppose a peripheral needs to be configured to transmit data.
There is an SFR bit which indicates that the peripheral is ready to transmit.
The firmware should check the bit and will only transmit data when the
peripheral is ready. When the firmware starts polling the SFR, the peripheral
could be busy transmitting/receiving other data so the firmware must wait
till that completes. Assuming that there is no other way, the
firmware shouldn't wait indefinitely.

The function sbi_timer_waitms_until() will constantly check whether a certain
condition is met, or timeout occurs. It can be used for the cases when a
timeout is required.

Signed-off-by: Adnan Rahman Chowdhury <adnan.chowdhury at sifive.com>
---
 include/sbi/sbi_timer.h |  3 +++
 lib/sbi/sbi_timer.c     | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/sbi/sbi_timer.h b/include/sbi/sbi_timer.h
index 63ef1af..ea3dbdd 100644
--- a/include/sbi/sbi_timer.h
+++ b/include/sbi/sbi_timer.h
@@ -48,6 +48,9 @@ static inline void sbi_timer_udelay(ulong usecs)
 	sbi_timer_delay_loop(usecs, 1000000, NULL, NULL);
 }
 
+bool sbi_timer_waitms_until(bool (*predicate)(void *), void *arg,
+			    uint64_t timeout_ms);
+
 /** Get timer value for current HART */
 u64 sbi_timer_value(void);
 
diff --git a/lib/sbi/sbi_timer.c b/lib/sbi/sbi_timer.c
index acdba92..d93036d 100644
--- a/lib/sbi/sbi_timer.c
+++ b/lib/sbi/sbi_timer.c
@@ -81,6 +81,24 @@ void sbi_timer_delay_loop(ulong units, u64 unit_freq,
 		delay_fn(opaque);
 }
 
+bool sbi_timer_waitms_until(bool(*predicate)(void*), void* arg,
+			    uint64_t timeout_ms)
+{
+	bool ret = true;
+	uint64_t start_time = sbi_timer_value();
+	uint64_t ticks =
+		(sbi_timer_get_device()->timer_freq / 1000) *
+		(timeout_ms);
+	do {
+		if (predicate(arg))
+			break;
+		if (sbi_timer_value() - start_time  >= ticks)
+			ret = false;
+	} while(ret);
+
+	return ret;
+}
+
 u64 sbi_timer_value(void)
 {
 	if (get_time_val)
-- 
2.30.2