[PATCH] staging: axis-fifo: fix tx_fifo_depth underflow in write

[LiuJunyuan <2058432396@qq.com>]

Check fifo->tx_fifo_depth before subtracting four words to avoid an
unsigned underflow when the device tree provides an invalid depth.

Signed-off-by: LiuJunyuan <2058432396@qq.com>
---
 drivers/staging/axis-fifo/axis-fifo.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/axis-fifo/axis-fifo.c b/drivers/staging/axis-fifo/axis-fifo.c
index 7bb35e11d1dd..178514a71734 100644
--- a/drivers/staging/axis-fifo/axis-fifo.c
+++ b/drivers/staging/axis-fifo/axis-fifo.c
@@ -228,7 +228,8 @@ static ssize_t axis_fifo_write(struct file *f, const char __user *buf,
 	 * raised, which requires a reset of the TX circuit to recover.
 	 */
 	if (!words_to_write || (len % sizeof(u32)) ||
-	    (words_to_write > (fifo->tx_fifo_depth - 4)))
+	    (fifo->tx_fifo_depth <= 4) ||
+	    (words_to_write > fifo->tx_fifo_depth - 4))
 		return -EINVAL;
 
 	if (f->f_flags & O_NONBLOCK) {
-- 
2.43.0