linux-kernel - Re: [PATCH v2 2/2] serial: mxs-auart: fix tx

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Message-ID: <qrark2grtpr7lpiffstvijod4ipp5ciz7ehigakdiu22semhkl@dawjy6nazccp>
Date: Thu, 01 Feb 2024 15:49:06 +0000
From: Emil Kronborg <emil.kronborg@...tonmail.com>
To: "Jiri Slaby (SUSE)" <jirislaby@...nel.org>
Cc: gregkh@...uxfoundation.org, linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] serial: mxs-auart: fix tx

On Thu, Feb 01, 2024 at 11:55 +0100, Jiri Slaby (SUSE) wrote:
> Emil reports:
>   After updating Linux on an i.MX28 board, serial communication over
>   AUART broke. When I TX from the board and measure on the TX pin, it
>   seems like the HW fifo is not emptied before the transmission is
>   stopped.
> 
> MXS performs weird things with stop_tx(). The driver makes it
> conditional on uart_tx_stopped().
> 
> So the driver needs special handling. Pass the brand new UART_TX_NOSTOP
> to uart_port_tx_flags() and handle the stop on its own.
> 
> Signed-off-by: Jiri Slaby (SUSE) <jirislaby@...nel.org>
> Reported-by: Emil Kronborg <emil.kronborg@...tonmail.com>
> Fixes: 2d141e683e9a ("tty: serial: use uart_port_tx() helper")
> Closes: https://lore.kernel.org/all/miwgbnvy3hjpnricubg76ytpn7xoceehwahupy25bubbduu23s@om2lptpa26xw/
> ---
>  drivers/tty/serial/mxs-auart.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
> index 3ec725555bcc..4749331fe618 100644
> --- a/drivers/tty/serial/mxs-auart.c
> +++ b/drivers/tty/serial/mxs-auart.c
> @@ -605,13 +605,16 @@ static void mxs_auart_tx_chars(struct mxs_auart_port *s)
>  		return;
>  	}
> 
> -	pending = uart_port_tx(&s->port, ch,
> +	pending = uart_port_tx_flags(&s->port, ch, UART_TX_NOSTOP,
>  		!(mxs_read(s, REG_STAT) & AUART_STAT_TXFF),
>  		mxs_write(ch, s, REG_DATA));
>  	if (pending)
>  		mxs_set(AUART_INTR_TXIEN, s, REG_INTR);
>  	else
>  		mxs_clr(AUART_INTR_TXIEN, s, REG_INTR);
> +
> +	if (uart_tx_stopped(&s->port))
> +               mxs_auart_stop_tx(&s->port);
>  }
> 
>  static void mxs_auart_rx_char(struct mxs_auart_port *s)
> --
> 2.43.0
> 

Tested on i.MX28.

Tested-by: Emil Kronborg <emil.kronborg@...tonmail.com>

-- 
Emil Kronborg