linux-kernel - Re: [PATCH v3] tty/serial: atmel: fix out of range clock divider handling

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Message-ID: <20191216102656.lkazcvuy5oai63lb@M43218.corp.atmel.com>
Date:   Mon, 16 Dec 2019 11:26:56 +0100
From:   Ludovic Desroches <ludovic.desroches@...rochip.com>
To:     David Engraf <david.engraf@...go.com>
CC:     <richard.genoud@...il.com>, <gregkh@...uxfoundation.org>,
        <jslaby@...e.com>, <nicolas.ferre@...rochip.com>,
        <alexandre.belloni@...tlin.com>, <linux-serial@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] tty/serial: atmel: fix out of range clock divider
 handling

On Mon, Dec 16, 2019 at 09:54:03AM +0100, David Engraf wrote:
> Use MCK_DIV8 when the clock divider is > 65535. Unfortunately the mode
> register was already written thus the clock selection is ignored.
> 
> Fix by doing the baud rate calulation before setting the mode.
> 
> Fixes: 5bf5635ac170 ("tty/serial: atmel: add fractional baud rate support")
> Signed-off-by: David Engraf <david.engraf@...go.com>
Acked-by: Ludovic Desroches <ludovic.desroches@...rochip.com>

Thanks for the fix

Regards

> ---
> Changes since v1:
>  - moves set baud rate block before setting the mode register because
>    ATMEL_US_RTSDIS and ATMEL_US_RTSEN depend on ATMEL_US_MR.mode
> 
> ---
>  drivers/tty/serial/atmel_serial.c | 43 ++++++++++++++++---------------
>  1 file changed, 22 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index a8dc8af83f39..1ba9bc667e13 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -2270,27 +2270,6 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>                 mode |= ATMEL_US_USMODE_NORMAL;
>         }
> 
> -       /* set the mode, clock divisor, parity, stop bits and data size */
> -       atmel_uart_writel(port, ATMEL_US_MR, mode);
> -
> -       /*
> -        * when switching the mode, set the RTS line state according to the
> -        * new mode, otherwise keep the former state
> -        */
> -       if ((old_mode & ATMEL_US_USMODE) != (mode & ATMEL_US_USMODE)) {
> -               unsigned int rts_state;
> -
> -               if ((mode & ATMEL_US_USMODE) == ATMEL_US_USMODE_HWHS) {
> -                       /* let the hardware control the RTS line */
> -                       rts_state = ATMEL_US_RTSDIS;
> -               } else {
> -                       /* force RTS line to low level */
> -                       rts_state = ATMEL_US_RTSEN;
> -               }
> -
> -               atmel_uart_writel(port, ATMEL_US_CR, rts_state);
> -       }
> -
>         /*
>          * Set the baud rate:
>          * Fractional baudrate allows to setup output frequency more
> @@ -2317,6 +2296,28 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
> 
>         if (!(port->iso7816.flags & SER_ISO7816_ENABLED))
>                 atmel_uart_writel(port, ATMEL_US_BRGR, quot);
> +
> +       /* set the mode, clock divisor, parity, stop bits and data size */
> +       atmel_uart_writel(port, ATMEL_US_MR, mode);
> +
> +       /*
> +        * when switching the mode, set the RTS line state according to the
> +        * new mode, otherwise keep the former state
> +        */
> +       if ((old_mode & ATMEL_US_USMODE) != (mode & ATMEL_US_USMODE)) {
> +               unsigned int rts_state;
> +
> +               if ((mode & ATMEL_US_USMODE) == ATMEL_US_USMODE_HWHS) {
> +                       /* let the hardware control the RTS line */
> +                       rts_state = ATMEL_US_RTSDIS;
> +               } else {
> +                       /* force RTS line to low level */
> +                       rts_state = ATMEL_US_RTSEN;
> +               }
> +
> +               atmel_uart_writel(port, ATMEL_US_CR, rts_state);
> +       }
> +
>         atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_RSTSTA | ATMEL_US_RSTRX);
>         atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN | ATMEL_US_RXEN);
>         atmel_port->tx_stopped = false;
> --
> 2.17.1
>