staging: axis-fifo: flush RX FIFO on read errors

commit 82a051e2553b9e297cba82a975d9c538b882c79e upstream.

Flush stale data from the RX FIFO in case of errors, to avoid reading
old data when new packets arrive.

Commit c6e8d85fafa7 ("staging: axis-fifo: Remove hardware resets for
user errors") removed full FIFO resets from the read error paths, which
fixed potential TX data losses, but introduced this RX issue.

Fixes: c6e8d85fafa7 ("staging: axis-fifo: Remove hardware resets for user errors")
Cc: stable@vger.kernel.org
Signed-off-by: Ovidiu Panait <ovidiu.panait.oss@gmail.com>
Link: https://lore.kernel.org/r/20250912101322.1282507-2-ovidiu.panait.oss@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 11 insertions, 7 deletions

diff --git a/drivers/staging/axis-fifo/axis-fifo.c b/drivers/staging/axis-fifo/axis-fifo.c
index b587d1c7a724..028ed5d0ecbe 100644
--- a/drivers/staging/axis-fifo/axis-fifo.c
+++ b/drivers/staging/axis-fifo/axis-fifo.c
@@ -391,6 +391,7 @@ static ssize_t axis_fifo_read(struct file *f, char __user *buf,
 	}
 
 	bytes_available = ioread32(fifo->base_addr + XLLF_RLR_OFFSET);
+	words_available = bytes_available / sizeof(u32);
 	if (!bytes_available) {
 		dev_err(fifo->dt_device, "received a packet of length 0\n");
 		ret = -EIO;
@@ -401,7 +402,7 @@ static ssize_t axis_fifo_read(struct file *f, char __user *buf,
 		dev_err(fifo->dt_device, "user read buffer too small (available bytes=%zu user buffer bytes=%zu)\n",
 			bytes_available, len);
 		ret = -EINVAL;
-		goto end_unlock;
+		goto err_flush_rx;
 	}
 
 	if (bytes_available % sizeof(u32)) {
@@ -410,11 +411,9 @@ static ssize_t axis_fifo_read(struct file *f, char __user *buf,
 		 */
 		dev_err(fifo->dt_device, "received a packet that isn't word-aligned\n");
 		ret = -EIO;
-		goto end_unlock;
+		goto err_flush_rx;
 	}
 
-	words_available = bytes_available / sizeof(u32);
-
 	/* read data into an intermediate buffer, copying the contents
 	 * to userspace when the buffer is full
 	 */
@@ -426,18 +425,23 @@ static ssize_t axis_fifo_read(struct file *f, char __user *buf,
 			tmp_buf[i] = ioread32(fifo->base_addr +
 					      XLLF_RDFD_OFFSET);
 		}
+		words_available -= copy;
 
 		if (copy_to_user(buf + copied * sizeof(u32), tmp_buf,
 				 copy * sizeof(u32))) {
 			ret = -EFAULT;
-			goto end_unlock;
+			goto err_flush_rx;
 		}
 
 		copied += copy;
-		words_available -= copy;
 	}
+	mutex_unlock(&fifo->read_lock);
+
+	return bytes_available;
 
-	ret = bytes_available;
+err_flush_rx:
+	while (words_available--)
+		ioread32(fifo->base_addr + XLLF_RDFD_OFFSET);
 
 end_unlock:
 	mutex_unlock(&fifo->read_lock);