+/*
+ * Calculate how much tail room is available
+ *
+ * Note the trick here. This path is ONLY caleed for Case A (see
+ * i2400m_tx_fifo_push() below), where we have:
+ *
+ * Case A
+ * N ___________
+ * | tail room |
+ * | |
+ * |<- IN ->|
+ * | |
+ * | data |
+ * | |
+ * |<- OUT ->|
+ * | |
+ * | head room |
+ * 0 -----------
+ *
+ * When calculating the tail_room, tx_in might get to be zero if
+ * i2400m->tx_in is right at the end of the buffer (really full
+ * buffer) if there is no head room. In this case, tail_room would be
+ * I2400M_TX_BUF_SIZE, although it is actually zero. Hence the final
+ * mod (%) operation. However, when doing this kind of optimization,
+ * i2400m->tx_in being zero would fail, so we treat is an a special
+ * case.
+ */
+static inline
+size_t __i2400m_tx_tail_room(struct i2400m *i2400m)
+{
+ size_t tail_room;
+ size_t tx_in;
+
+ if (unlikely(i2400m->tx_in) == 0)
+ return I2400M_TX_BUF_SIZE;
+ tx_in = i2400m->tx_in % I2400M_TX_BUF_SIZE;
+ tail_room = I2400M_TX_BUF_SIZE - tx_in;
+ tail_room %= I2400M_TX_BUF_SIZE;
+ return tail_room;
+}
+
+