Re: [PATCH v1] serial: qcom_geni: Fix RX DMA stall when SE_DMA_RX_LEN_IN is zero

[Greg Kroah-Hartman]

On Thu, May 28, 2026 at 12:35:43PM +0530, Viken Dadhaniya wrote:
> In qcom_geni_serial_handle_rx_dma(), geni_se_rx_dma_unprep() clears
> port->rx_dma_addr before SE_DMA_RX_LEN_IN is read. If the register is zero,
> for example when the RX stale counter fires on an idle line, the handler
> returns without calling geni_se_rx_dma_prep().
> 
> The next RX DMA interrupt then hits the !port->rx_dma_addr guard and
> returns immediately, so the RX DMA buffer is never rearmed and later input
> is lost.
> 
> Keep the handler on the rearm path when rx_in is zero. Warn about the
> unexpected zero-length DMA completion, skip received-data handling, and
> always call geni_se_rx_dma_prep().
> 
> Fixes: 2aaa43c70778 ("tty: serial: qcom-geni-serial: add support for serial engine DMA")
> Signed-off-by: Viken Dadhaniya <viken.dadhaniya@xxxxxxxxxxxxxxxx>
> ---
>  drivers/tty/serial/qcom_geni_serial.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index d81b539cff7f..7ead87b4eb65 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -905,12 +905,9 @@ static void qcom_geni_serial_handle_rx_dma(struct uart_port *uport, bool drop)
>  	port->rx_dma_addr = 0;
>  
>  	rx_in = readl(uport->membase + SE_DMA_RX_LEN_IN);
> -	if (!rx_in) {
> -		dev_warn(uport->dev, "serial engine reports 0 RX bytes in!\n");
> -		return;
> -	}
> -
> -	if (!drop)
> +	if (!rx_in)
> +		dev_warn_ratelimited(uport->dev, "serial engine reports 0 RX bytes in!\n");
> +	else if (!drop)
>  		handle_rx_uart(uport, rx_in);
>  
>  	ret = geni_se_rx_dma_prep(&port->se, port->rx_buf,
> 
> ---
> base-commit: e7d700e14934e68f86338c5610cf2ae76798b663
> change-id: 20260528-serial-rx-0-byte-fix-ec9d08cfe78e
> 
> Best regards,
> --  
> Viken Dadhaniya <viken.dadhaniya@xxxxxxxxxxxxxxxx>
> 
> 

Hi,

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