@@ -278,6 +278,48 @@ enum {
#define TAIL_FULL ((void *)~(unsigned long)NULL)
/*
+ * 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;
+}
+
+
+/*
* Allocate @size bytes in the TX fifo, return a pointer to it
*
* @i2400m: device descriptor
@@ -338,7 +380,7 @@ void *i2400m_tx_fifo_push(struct i2400m *i2400m, size_t size, size_t padding)
return NULL;
}
/* Is there space at the tail? */
- tail_room = I2400M_TX_BUF_SIZE - i2400m->tx_in % I2400M_TX_BUF_SIZE;
+ tail_room = __i2400m_tx_tail_room(i2400m);
if (tail_room < needed_size) {
if (i2400m->tx_out % I2400M_TX_BUF_SIZE
< i2400m->tx_in % I2400M_TX_BUF_SIZE) {
@@ -367,17 +409,29 @@ void *i2400m_tx_fifo_push(struct i2400m *i2400m, size_t size, size_t padding)
* (I2400M_PL_PAD for the payloads, I2400M_TX_PLD_SIZE for the
* header).
*
+ * Tail room can get to be zero if a message was opened when there was
+ * space only for a header. _tx_close() will mark it as to-skip (as it
+ * will have no payloads) and there will be no more space to flush, so
+ * nothing has to be done here. This is probably cheaper than ensuring
+ * in _tx_new() that there is some space for payloads...as we could
+ * always possibly hit the same problem if the payload wouldn't fit.
+ *
* Note:
*
* Assumes i2400m->tx_lock is taken, and we use that as a barrier
+ *
+ * This path is only taken for Case A FIFO situations [see
+ * i2400m_tx_fifo_push()]
*/
static
void i2400m_tx_skip_tail(struct i2400m *i2400m)
{
struct device *dev = i2400m_dev(i2400m);
size_t tx_in = i2400m->tx_in % I2400M_TX_BUF_SIZE;
- size_t tail_room = I2400M_TX_BUF_SIZE - tx_in;
+ size_t tail_room = __i2400m_tx_tail_room(i2400m);
struct i2400m_msg_hdr *msg = i2400m->tx_buf + tx_in;
+ if (unlikely(tail_room == 0))
+ return;
BUG_ON(tail_room < sizeof(*msg));
msg->size = tail_room | I2400M_TX_SKIP;
d_printf(2, dev, "skip tail: skipping %zu bytes @%zu\n",
i2400m_tx_skip_tail() needs to handle the special case of being called when the tail room that is left over in the FIFO is zero. This happens when a TX message header was opened at the very end of the FIFO (without payloads). The i2400m_tx_close() code already marked said TX message (header) to be skipped and this function should be doing nothing. It is called anyway because it is part of a common "corner case" path handling which takes care of more cases than only this one. The tail room computation was also improved to take care of the case when tx_in is at the end of the buffer boundary; tail_room has to be modded (%) to the buffer size. To do that in a single well-documented place, __i2400m_tx_tail_room() is introduced and used. Treat i2400m->tx_in == 0 as a corner case and handle it accordingly. Found and diagnosed by Cindy H. Kao. Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com> --- drivers/net/wimax/i2400m/tx.c | 58 +++++++++++++++++++++++++++++++++++++++- 1 files changed, 56 insertions(+), 2 deletions(-)