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 12:07:53 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Sherry Sun <sherry.sun@....com>
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 Sun, Aug 21, 2022 at 10:01:45AM +0000, Sherry Sun wrote:
> > 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?

Yes please.