vfs/poll: round timeout up to next full tick. Calling poll() with timeout less than half tick (thus MSEC2TICK(timeout) => 0) caused returning error with EAGAIN. Instead of rounding timeout down, value should be rounded up. Open Group spec for poll says: "Implementations may place limitations on the granularity of timeout intervals. If the requested timeout interval requires a finer granularity than the implementation supports, the actual timeout interval will be rounded up to the next supported value."

fs/vfs/fs_poll.c

@@ -388,6 +388,25 @@ int poll(FAR struct pollfd *fds, nfds_t nfds, int timeout)
         }
       else if (timeout > 0)
         {
+          systime_t ticks;
+
+          /* "Implementations may place limitations on the granularity of
+           * timeout intervals. If the requested timeout interval requires
+           * a finer granularity than the implementation supports, the
+           * actual timeout interval will be rounded up to the next
+           * supported value." -- opengroup.org
+           *
+           * Round timeout up to next full tick.
+           */
+
+#if (MSEC_PER_TICK * USEC_PER_MSEC) != USEC_PER_TICK && \
+    defined(CONFIG_HAVE_LONG_LONG)
+          ticks = ((long long)timeout * USEC_PER_MSEC) + (USEC_PER_TICK - 1) /
+                  USEC_PER_TICK;
+#else
+          ticks = (timeout + (MSEC_PER_TICK - 1)) / MSEC_PER_TICK;
+#endif
+
           /* Either wait for either a poll event(s), for a signal to occur,
            * or for the specified timeout to elapse with no event.
            *
@@ -396,7 +415,7 @@ int poll(FAR struct pollfd *fds, nfds_t nfds, int timeout)
            * immediately.
            */
 
-           ret = sem_tickwait(&sem, clock_systimer(), MSEC2TICK(timeout));
+           ret = sem_tickwait(&sem, clock_systimer(), ticks);
            if (ret < 0)
              {
                if (ret == -ETIMEDOUT)