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

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Message-ID: <DB9PR04MB84110E4B09CC05573584724F926E9@DB9PR04MB8411.eurprd04.prod.outlook.com>
Date:   Sun, 21 Aug 2022 10:01:45 +0000
From:   Sherry Sun <sherry.sun@....com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <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?

This issue existed when the lpuart32_set_termios() was introduced. So the Fixes tag should be:
Fixes: 380c966c093e ("tty: serial: fsl_lpuart: add 32-bit register interface support"), and I believe it can be backported to the older stable kernels.

Should I send a V2 patch to add the Fixes tag?

Best regards
Sherry

> 
> thanks,
> 
> greg k-h