linux-kernel - Re: [PATCH 1/2] serial: 8250: 8250_omap.c: Add support for handling UART error conditions

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Message-ID: <21a85fdd-d462-48f5-b145-9eb7000bf96b@ti.com>
Date: Tue, 20 Jan 2026 10:58:27 +0530
From: "Kumar, Udit" <u-kumar1@...com>
To: Moteen Shah <m-shah@...com>, <gregkh@...uxfoundation.org>,
	<jirislaby@...nel.org>
CC: <linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>,
	<vigneshr@...com>, <gehariprasath@...com>, <g-praveen@...com>,
	<j-keerthy@...com>, <u-kumar1@...com>
Subject: Re: [PATCH 1/2] serial: 8250: 8250_omap.c: Add support for handling
 UART error conditions

please check subject of patch

On 1/12/2026 1:48 PM, Moteen Shah wrote:
> The DMA IRQ handler does not accounts for the overrun(OE) or any other
accounts to account
> errors being reported by the IP before triggering a DMA transaction which
transaction, which
> leads to the interrupts not being handled resulting into an IRQ storm.
>
> The way to handle OE is to:
> 1. Reset the RX FIFO.
> 2. Read the UART_RESUME register, which clears the internal flag
>
> Earlier, the driver issued DMA transations even in case of OE which shouldn't

transations to transactions

> be done according to the OE handling mechanism mentioned above, as we are
> resetting the FIFO's, refer section: "12.1.6.4.8.1.3.6 Overrun During

FIFO's to FIFO

> Receive" [0].
>
> [0] https://www.ti.com/lit/pdf/spruiu1
>
> Signed-off-by: Moteen Shah <m-shah@...com>
> ---
>   drivers/tty/serial/8250/8250_omap.c | 23 +++++++++++++++++++++--
>   1 file changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index 9e49ef48b851..e26bae0a6488 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -100,6 +100,9 @@
>   #define OMAP_UART_REV_52 0x0502
>   #define OMAP_UART_REV_63 0x0603
>   
> +/* Resume register */
> +#define UART_OMAP_RESUME		0x0B
> +
>   /* Interrupt Enable Register 2 */
>   #define UART_OMAP_IER2			0x1B
>   #define UART_OMAP_IER2_RHR_IT_DIS	BIT(2)
> @@ -119,7 +122,6 @@
>   /* Timeout low and High */
>   #define UART_OMAP_TO_L                 0x26
>   #define UART_OMAP_TO_H                 0x27
> -
>   struct omap8250_priv {
>   	void __iomem *membase;
>   	int line;
> @@ -1256,6 +1258,20 @@ static u16 omap_8250_handle_rx_dma(struct uart_8250_port *up, u8 iir, u16 status
>   	return status;
>   }
>   
> +static void am654_8250_handle_uart_errors(struct uart_8250_port *up, u8 iir, u16 status)
> +{
> +	if (status & UART_LSR_OE) {
> +		serial8250_clear_and_reinit_fifos(up);
> +		serial_in(up, UART_LSR);
> +		serial_in(up, UART_OMAP_RESUME);
> +	} else {
> +		if (status & (UART_LSR_FE | UART_LSR_PE | UART_LSR_BI))
> +			serial_in(up, UART_RX);
> +		if (iir & UART_IIR_XOFF)
> +			serial_in(up, UART_IIR);
> +	}
> +}
> +
>   static void am654_8250_handle_rx_dma(struct uart_8250_port *up, u8 iir,
>   				     u16 status)
>   {
> @@ -1266,7 +1282,8 @@ static void am654_8250_handle_rx_dma(struct uart_8250_port *up, u8 iir,
>   	 * Queue a new transfer if FIFO has data.
>   	 */
>   	if ((status & (UART_LSR_DR | UART_LSR_BI)) &&
> -	    (up->ier & UART_IER_RDI)) {
> +	    (up->ier & UART_IER_RDI) && !(status & UART_LSR_OE)) {
> +		am654_8250_handle_uart_errors(up, iir, status);

may be you can think of splitting error handing into 2 functions ie 
handle BI or so and OE error.

when you call above function am654_8250_handle_uart_errors, first 
condition will be always false.


>   		omap_8250_rx_dma(up);
>   		serial_out(up, UART_OMAP_EFR2, UART_OMAP_EFR2_TIMEOUT_BEHAVE);
>   	} else if ((iir & 0x3f) == UART_IIR_RX_TIMEOUT) {
> @@ -1282,6 +1299,8 @@ static void am654_8250_handle_rx_dma(struct uart_8250_port *up, u8 iir,
>   		serial_out(up, UART_OMAP_EFR2, 0x0);
>   		up->ier |= UART_IER_RLSI | UART_IER_RDI;
>   		serial_out(up, UART_IER, up->ier);
> +	} else {
> +		am654_8250_handle_uart_errors(up, iir, status);

I assume , you will hit this else only case of OE ? , if yes then do you 
think, call to error handling should be conditional ?


>   	}
>   }
>