Since commit 2ca34b508774 ("staging: axis-fifo: Correct handling of tx_fifo_depth for size validation"), write() operations with packets larger than 'tx_fifo_depth - 4' words are no longer rejected with -EINVAL.

Fortunately, the packets are not actually getting transmitted to hardware, otherwise they would be raising a 'Transmit Packet Overrun Error' interrupt, which requires a reset of the TX circuit to recover from.

Instead, the request times out inside wait_event_interruptible_timeout() and always returns -EAGAIN, since the wake up condition can never be true for these packets. But still, they unnecessarily block other tasks from writing to the FIFO and the EAGAIN return code signals userspace to retry the write() call, even though it will always fail and time out.

According to the AXI4-Stream FIFO reference manual (PG080), the maximum valid packet length is 'tx_fifo_depth - 4' words, so attempting to send larger packets is invalid and should not be happening in the first place:

The maximum packet that can be transmitted is limited by the size of the FIFO, which is (C_TX_FIFO_DEPTH–4)*(data interface width/8) bytes.

Therefore, bring back the old behavior and outright reject packets larger than 'tx_fifo_depth - 4' with -EINVAL. Add a comment to explain why the check is necessary. The dev_err() message was removed to avoid cluttering the dmesg log if an invalid packet is received from userspace.

Fixes: 2ca34b508774 ("staging: axis-fifo: Correct handling of tx_fifo_depth for size validation") Cc: stable@vger.kernel.org Signed-off-by: Ovidiu Panait ovidiu.panait.oss@gmail.com --- Changes in v2: - added "cc: stable" tag

drivers/staging/axis-fifo/axis-fifo.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/axis-fifo/axis-fifo.c b/drivers/staging/axis-fifo/axis-fifo.c index e8aa632e0a31..271236ad023f 100644 --- a/drivers/staging/axis-fifo/axis-fifo.c +++ b/drivers/staging/axis-fifo/axis-fifo.c @@ -325,11 +325,17 @@ static ssize_t axis_fifo_write(struct file *f, const char __user *buf, return -EINVAL; }

- if (words_to_write > fifo->tx_fifo_depth) { - dev_err(fifo->dt_device, "tried to write more words [%u] than slots in the fifo buffer [%u]\n", - words_to_write, fifo->tx_fifo_depth); + /* + * In 'Store-and-Forward' mode, the maximum packet that can be + * transmitted is limited by the size of the FIFO, which is + * (C_TX_FIFO_DEPTH–4)*(data interface width/8) bytes. + * + * Do not attempt to send a packet larger than 'tx_fifo_depth - 4', + * otherwise a 'Transmit Packet Overrun Error' interrupt will be + * raised, which requires a reset of the TX circuit to recover. + */ + if (words_to_write > (fifo->tx_fifo_depth - 4)) return -EINVAL; - }

if (fifo->write_flags & O_NONBLOCK) { /*