linux-kernel - [PATCH v2 3/3] serial: qcom-geni: do not kill the machine on fifo underrun

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Message-ID: <20240704101805.30612-4-johan+linaro@kernel.org>
Date: Thu,  4 Jul 2024 12:18:05 +0200
From: Johan Hovold <johan+linaro@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>
Cc: Douglas Anderson <dianders@...omium.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Bjorn Andersson <andersson@...nel.org>,
	linux-arm-msm@...r.kernel.org,
	linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Johan Hovold <johan+linaro@...nel.org>
Subject: [PATCH v2 3/3] serial: qcom-geni: do not kill the machine on fifo underrun

The Qualcomm GENI serial driver did not handle buffer flushing and used
to print discarded characters when the circular buffer was cleared.
Since commit 1788cf6a91d9 ("tty: serial: switch from circ_buf to kfifo")
this instead resulted in a hard lockup due to
qcom_geni_serial_send_chunk_fifo() spinning indefinitely in the
interrupt handler.

The underlying bugs have now been fixed, but make sure to output NUL
characters instead of killing the machine if a similar driver bug is
ever reintroduced.

Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
---
 drivers/tty/serial/qcom_geni_serial.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index b2bbd2d79dbb..69a632fefc41 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -878,7 +878,7 @@ static void qcom_geni_serial_send_chunk_fifo(struct uart_port *uport,
 		memset(buf, 0, sizeof(buf));
 		tx_bytes = min(remaining, BYTES_PER_FIFO_WORD);
 
-		tx_bytes = uart_fifo_out(uport, buf, tx_bytes);
+		uart_fifo_out(uport, buf, tx_bytes);
 
 		iowrite32_rep(uport->membase + SE_GENI_TX_FIFOn, buf, 1);
 
-- 
2.44.1