The receiver should be enabled in the startup() callback and there is no
need to stop it on every termios update.

Since commit 6f3c3cafb115 ("serial: qcom-geni: disable interrupts during
console writes") the calls to manipulate the secondary interrupts, which
were done without holding the port lock, can lead to the receiver being
left disabled when set_termios() races with the console code (e.g. when
init opens the tty during boot).

Fixes: 6f3c3cafb115 ("serial: qcom-geni: disable interrupts during console writes")
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---
 drivers/tty/serial/qcom_geni_serial.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index 88ad5a6e7de2..85c2742e6cc4 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -1167,6 +1167,11 @@ static int qcom_geni_serial_startup(struct uart_port *uport)
 		if (ret)
 			return ret;
 	}
+
+	uart_port_lock_irq(uport);
+	qcom_geni_serial_start_rx(uport);
+	uart_port_unlock_irq(uport);
+
 	enable_irq(uport->irq);
 
 	return 0;
@@ -1252,7 +1257,6 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport,
 	unsigned int avg_bw_core;
 	unsigned long timeout;
 
-	qcom_geni_serial_stop_rx(uport);
 	/* baud rate */
 	baud = uart_get_baud_rate(uport, termios, old, 300, 4000000);
 
@@ -1268,7 +1272,7 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport,
 		dev_err(port->se.dev,
 			"Couldn't find suitable clock rate for %u\n",
 			baud * sampling_rate);
-		goto out_restart_rx;
+		return;
 	}
 
 	dev_dbg(port->se.dev, "desired_rate = %u, clk_rate = %lu, clk_div = %u\n",
@@ -1359,8 +1363,6 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport,
 	writel(stop_bit_len, uport->membase + SE_UART_TX_STOP_BIT_LEN);
 	writel(ser_clk_cfg, uport->membase + GENI_SER_M_CLK_CFG);
 	writel(ser_clk_cfg, uport->membase + GENI_SER_S_CLK_CFG);
-out_restart_rx:
-	qcom_geni_serial_start_rx(uport);
 }
 
 #ifdef CONFIG_SERIAL_QCOM_GENI_CONSOLE
-- 
2.44.2

On Mon, Sep 16, 2024 at 07:26:42PM +0200, Johan Hovold wrote:
> The receiver should be enabled in the startup() callback and there is no
> need to stop it on every termios update.
> 
> Since commit 6f3c3cafb115 ("serial: qcom-geni: disable interrupts during
> console writes") the calls to manipulate the secondary interrupts, which
> were done without holding the port lock, can lead to the receiver being
> left disabled when set_termios() races with the console code (e.g. when
> init opens the tty during boot).
> 
> Fixes: 6f3c3cafb115 ("serial: qcom-geni: disable interrupts during console writes")
> Signed-off-by: Johan Hovold <johan+linaro@kernel.org>

Turns out the DMA implementation is broken and currently depends on
these bogus calls to stop and restart rx in set_termios().

I won't have time to look at this for a couple of weeks due to
conferences, so please hold off on merging these until I'm back.

Johan