Regression: serial: imx: overrun errors on debug UART

[Fabio Estevam]

Hi Stefan,

On Fri, Mar 24, 2023 at 8:48 AM Ilpo Järvinen
<ilpo.jarvinen at linux.intel.com> wrote:

> This has come up earlier, see e.g.:
>
> https://lore.kernel.org/linux-serial/20221003110850.GA28338@francesco-nb.int.toradex.com/
>
> My somewhat uninformed suggestion: if the overrun problems mostly show up
> with console ports, maybe the trigger level could depend on the port
> being a console or not?

Does the change below help? Taking Ilpo's suggestion into account:

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 0fa1bd8cdec7..4d0aae38b7a5 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -233,6 +233,7 @@ struct imx_port {
        enum imx_tx_state       tx_state;
        struct hrtimer          trigger_start_tx;
        struct hrtimer          trigger_stop_tx;
+       unsigned int            rxtl;
 };

 struct imx_port_ucrs {
@@ -1309,6 +1310,7 @@ static void imx_uart_clear_rx_errors(struct
imx_port *sport)
 }

 #define TXTL_DEFAULT 2 /* reset default */
+#define RXTL_DEFAULT_CONSOLE 1 /* 1 character or aging timer */
 #define RXTL_DEFAULT 8 /* 8 characters or aging timer */
 #define TXTL_DMA 8 /* DMA burst setting */
 #define RXTL_DMA 9 /* DMA burst setting */
@@ -1422,7 +1424,7 @@ static void imx_uart_disable_dma(struct imx_port *sport)
        ucr1 &= ~(UCR1_RXDMAEN | UCR1_TXDMAEN | UCR1_ATDMAEN);
        imx_uart_writel(sport, ucr1, UCR1);

-       imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT);
+       imx_uart_setup_ufcr(sport, TXTL_DEFAULT, sport->rxtl);

        sport->dma_is_enabled = 0;
 }
@@ -1447,7 +1449,7 @@ static int imx_uart_startup(struct uart_port *port)
                return retval;
        }

-       imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT);
+       imx_uart_setup_ufcr(sport, TXTL_DEFAULT, sport->rxtl);

        /* disable the DREN bit (Data Ready interrupt enable) before
         * requesting IRQs
@@ -1464,6 +1466,11 @@ static int imx_uart_startup(struct uart_port *port)
        if (!uart_console(port) && imx_uart_dma_init(sport) == 0)
                dma_is_inited = 1;

+       if (uart_console(port))
+               sport->rxtl = RXTL_DEFAULT_CONSOLE;
+       else
+               sport->rxtl = RXTL_DEFAULT;
+
        spin_lock_irqsave(&sport->port.lock, flags);

        /* Reset fifo's and state machines */
@@ -1863,7 +1870,7 @@ static int imx_uart_poll_init(struct uart_port *port)
        if (retval)
                clk_disable_unprepare(sport->clk_ipg);

-       imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT);
+       imx_uart_setup_ufcr(sport, TXTL_DEFAULT, sport->rxtl);

        spin_lock_irqsave(&sport->port.lock, flags);

@@ -2139,7 +2146,7 @@ imx_uart_console_setup(struct console *co, char *options)
        else
                imx_uart_console_get_options(sport, &baud, &parity, &bits);

-       imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT);
+       imx_uart_setup_ufcr(sport, TXTL_DEFAULT, sport->rxtl);

        retval = uart_set_options(&sport->port, co, baud, parity, bits, flow);