Uart flow control on Jetson Nano

Robotics & Edge Computing Jetson & Embedded Systems Jetson Nano
,
9

hello choom.dongmued,

it seems RTS signal did not pulling down.
could you please try below to force the pin as low state.
for example,

--- a/drivers/tty/serial/serial-tegra.c
+++ b/drivers/tty/serial/serial-tegra.c
@@ -56,6 +56,7 @@
 #define TEGRA_UART_IER_EORD                    0x20
 #define TEGRA_UART_MCR_RTS_EN                  0x40
 #define TEGRA_UART_MCR_CTS_EN                  0x20
+#define TEGRA_UART_MCR_FORCE_RTS_LOW           0x02
 #define TEGRA_UART_LSR_ANY                     (UART_LSR_OE | UART_LSR_BI | \
                                                UART_LSR_PE | UART_LSR_FE)
 #define TEGRA_UART_IRDA_CSR                    0x08
@@ -1545,6 +1545,8 @@ static void tegra_uart_set_termios(struct uart_port *u,
                tty_termios_encode_baud_rate(termios, baud, baud);
        spin_lock_irqsave(&u->lock, flags);

+       tup->mcr_shadow &= ~TEGRA_UART_MCR_FORCE_RTS_LOW;

        /* Flow control */
        if (termios->c_cflag & CRTSCTS) {
                tup->mcr_shadow |= TEGRA_UART_MCR_CTS_EN;
@@ -1896,6 +1898,11 @@ static int tegra_uart_probe(struct platform_device *pdev)
                return ret;
        }

+       clk_prepare_enable(tup->uart_clk);
+       tup->mcr_shadow = TEGRA_UART_MCR_FORCE_RTS_LOW;
+       tegra_uart_write(tup, tup->mcr_shadow, UART_MCR);
+       clk_disable_unprepare(tup->uart_clk);
+
        if (tup->enable_rx_buffer_throttle) {
                setup_timer(&tup->timer, tegra_uart_rx_buffer_throttle_timer,