Make sleep threshold for delays configurable

This allows the minimum time that default_delay() will choose to sleep
for instead of polling to be configured at build-time. The default
remains unchanged at 100 milliseconds for now.

The test's correctness has been checked by testing with minimum sleep
time left at its default and set to a non-default value smaller than 100
microseconds (both pass without sleeping, verified with strace) and with
the minimum sleep time set to 0 (causing the test to be skipped). The
configured value from the macro needs to be stored in a const to avoid
-Werror=type-limits errors when configured to be zero.

Change-Id: Ida96e0816ac914ed69d6fd82ad90ebe89cdef1cc
Signed-off-by: Peter Marheine <pmarheine@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/81606
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>

tests/udelay.c

@@ -34,6 +34,8 @@ static uint64_t now_us(void) {
 #endif
 }
 
+static const int64_t min_sleep = CONFIG_DELAY_MINIMUM_SLEEP_US;
+
 /*
  * A short delay should delay for at least as long as requested,
  * and more than 10x as long would be worrisome.
@@ -43,9 +45,21 @@ static uint64_t now_us(void) {
  * test.
  */
 void udelay_test_short(void **state) {
+    /*
+     * Delay for 100 microseconds, or short enough that we won't sleep.
+     * It's not useful to test the sleep path because we assume the OS won't
+     * sleep for less time than we ask.
+     */
+    int64_t delay_us = 100;
+    if (delay_us >= min_sleep)
+      delay_us = min_sleep - 1;
+    /* No point in running this test if delay always sleeps. */
+    if (delay_us <= 0)
+      skip();
+
     uint64_t start = now_us();
-    default_delay(100);
+    default_delay(delay_us);
     uint64_t elapsed = now_us() - start;
 
-    assert_in_range(elapsed, 100, 1000);
+    assert_in_range(elapsed, delay_us, 10 * delay_us);
 }