linux-kernel - Re: [PATCH V2] tty: serial: lpuart: disable flow control while waiting for the transmit engine to complete

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Date:   Sun, 21 Aug 2022 10:38:26 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Sherry Sun <sherry.sun@....com>
Cc:     jirislaby@...nel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-imx@....com
Subject: Re: [PATCH V2] tty: serial: lpuart: disable flow control while
 waiting for the transmit engine to complete

On Thu, Aug 04, 2022 at 03:04:20PM +0800, Sherry Sun wrote:
> When the user initializes the uart port, and waits for the transmit
> engine to complete in lpuart32_set_termios(), if the UART TX fifo has
> dirty data and the UARTMODIR enable the flow control, the TX fifo may
> never be empty. So here we should disable the flow control first to make
> sure the transmit engin can complete.
> 
> Signed-off-by: Sherry Sun <sherry.sun@....com>
> ---
> Changes in V2:
> 1. Rephrase the commit log as suggested by Jiri.
> ---
>  drivers/tty/serial/fsl_lpuart.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
> index fc7d235a1e27..f0fccd2ff7ac 100644
> --- a/drivers/tty/serial/fsl_lpuart.c
> +++ b/drivers/tty/serial/fsl_lpuart.c
> @@ -2172,6 +2172,7 @@ lpuart32_set_termios(struct uart_port *port, struct ktermios *termios,
>  	uart_update_timeout(port, termios->c_cflag, baud);
>  
>  	/* wait transmit engin complete */
> +	lpuart32_write(&sport->port, 0, UARTMODIR);
>  	lpuart32_wait_bit_set(&sport->port, UARTSTAT, UARTSTAT_TC);
>  
>  	/* disable transmit and receive */
> -- 
> 2.17.1

What commit id does this fix?  Should it be backported to older stable
kernels?

thanks,

greg k-h