In qcom_geni_serial_handle_rx_dma(), geni_se_rx_dma_unprep() clears
port->rx_dma_addr before SE_DMA_RX_LEN_IN is read. If the register is zero,
for example when the RX stale counter fires on an idle line, the handler
returns without calling geni_se_rx_dma_prep().
The next RX DMA interrupt then hits the !port->rx_dma_addr guard and
returns immediately, so the RX DMA buffer is never rearmed and later input
is lost.
Keep the handler on the rearm path when rx_in is zero. Warn about the
unexpected zero-length DMA completion, skip received-data handling, and
always call geni_se_rx_dma_prep().
Fixes: 2aaa43c70778 ("tty: serial: qcom-geni-serial: add support for serial engine DMA")
Cc: stable@vger.kernel.org
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Viken Dadhaniya <viken.dadhaniya@oss.qualcomm.com>
---
Changes in v2:
- Add Cc: stable@vger.kernel.org tag (missed in v1)
- Link to v1: https://patch.msgid.link/20260528-serial-rx-0-byte-fix-v1-1-dc4e876c7368@oss.qualcomm.com
---
drivers/tty/serial/qcom_geni_serial.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)
diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index d81b539cff7f..7ead87b4eb65 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -905,12 +905,9 @@ static void qcom_geni_serial_handle_rx_dma(struct uart_port *uport, bool drop)
port->rx_dma_addr = 0;
rx_in = readl(uport->membase + SE_DMA_RX_LEN_IN);
- if (!rx_in) {
- dev_warn(uport->dev, "serial engine reports 0 RX bytes in!\n");
- return;
- }
-
- if (!drop)
+ if (!rx_in)
+ dev_warn_ratelimited(uport->dev, "serial engine reports 0 RX bytes in!\n");
+ else if (!drop)
handle_rx_uart(uport, rx_in);
ret = geni_se_rx_dma_prep(&port->se, port->rx_buf,
---
base-commit: e7d700e14934e68f86338c5610cf2ae76798b663
change-id: 20260528-serial-rx-0-byte-fix-ec9d08cfe78e
Best regards,
--
Viken Dadhaniya <viken.dadhaniya@oss.qualcomm.com>