timepoints: minimal compatibility with CONFIG_SYS_CLOCK_EXISTS=n

When timers are configured out, timepoint-based timeouts are reduced to
"no wait" or "wait forever" only.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>

include/zephyr/sys_clock.h

@@ -190,6 +190,8 @@ int64_t sys_clock_tick_get(void);
 #define sys_clock_tick_get_32() (0)
 #endif
 
+#ifdef CONFIG_SYS_CLOCK_EXISTS
+
 /**
  * @brief Kernel timepoint type
  *
@@ -236,31 +238,55 @@ k_timepoint_t sys_timepoint_calc(k_timeout_t timeout);
 k_timeout_t sys_timepoint_timeout(k_timepoint_t timepoint);
 
 /**
- * @brief Indicates if timepoint is expired
+ * @brief Provided for backward compatibility.
  *
- * @param timepoint Timepoint to evaluate
- * @retval true if the timepoint is in the past, false otherwise
+ * This is deprecated. Consider `sys_timepoint_calc()` instead.
  *
  * @see sys_timepoint_calc()
  */
-static inline bool sys_timepoint_expired(k_timepoint_t timepoint)
+__deprecated
+static inline uint64_t sys_clock_timeout_end_calc(k_timeout_t timeout)
 {
-	return K_TIMEOUT_EQ(sys_timepoint_timeout(timepoint), Z_TIMEOUT_NO_WAIT);
+	k_timepoint_t tp = sys_timepoint_calc(timeout);
+
+	return tp.tick;
+}
+
+#else
+
+/*
+ * When timers are configured out, timepoints can't relate to anything.
+ * The best we can do is to preserve whether or not they are derived from
+ * K_NO_WAIT. Anything else will translate back to K_FOREVER.
+ */
+typedef struct { bool wait; } k_timepoint_t;
+
+static inline k_timepoint_t sys_timepoint_calc(k_timeout_t timeout)
+{
+	k_timepoint_t timepoint;
+
+	timepoint.wait = !K_TIMEOUT_EQ(timeout, Z_TIMEOUT_NO_WAIT);
+	return timepoint;
+}
+
+static inline k_timeout_t sys_timepoint_timeout(k_timepoint_t timepoint)
+{
+	return timepoint.wait ? Z_FOREVER : Z_TIMEOUT_NO_WAIT;
 }
 
+#endif
+
 /**
- * @brief Provided for backward compatibility.
+ * @brief Indicates if timepoint is expired
  *
- * This is deprecated. Consider `sys_timepoint_calc()` instead.
+ * @param timepoint Timepoint to evaluate
+ * @retval true if the timepoint is in the past, false otherwise
  *
  * @see sys_timepoint_calc()
  */
-__deprecated
-static inline uint64_t sys_clock_timeout_end_calc(k_timeout_t timeout)
+static inline bool sys_timepoint_expired(k_timepoint_t timepoint)
 {
-	k_timepoint_t tp = sys_timepoint_calc(timeout);
-
-	return tp.tick;
+	return K_TIMEOUT_EQ(sys_timepoint_timeout(timepoint), Z_TIMEOUT_NO_WAIT);
 }
 
 #ifdef __cplusplus