linux-kernel - Re: [PATCH] serial: mvebu-uart: correctly report configured baudrate value

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Date:   Tue, 28 Jun 2022 13:23:34 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Pali Rohár <pali@...nel.org>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Allen Yan <yanwei@...vell.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Gregory CLEMENT <gregory.clement@...tlin.com>,
        linux-serial <linux-serial@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] serial: mvebu-uart: correctly report configured baudrate
 value

On Tue, 28 Jun 2022, Pali Rohár wrote:

> Functions tty_termios_encode_baud_rate() and uart_update_timeout() should
> be called with the baudrate value which was set to hardware. Linux then
> report exact values via ioctl(TCGETS2) to userspace.
> 
> Change mvebu_uart_baud_rate_set() function to return baudrate value which
> was set to hardware and propagate this value to above mentioned functions.
> 
> With this change userspace would see precise value in termios c_ospeed
> field.
> 
> Signed-off-by: Pali Rohár <pali@...nel.org>
> Fixes: 68a0db1d7da2 ("serial: mvebu-uart: add function to change baudrate")

Look better than my patch covering cases I didn't even realize
existed. Thanks.

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

-- 
 i.


> ---
>  drivers/tty/serial/mvebu-uart.c | 25 +++++++++++++------------
>  1 file changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
> index 0429c2a54290..93489fe334d0 100644
> --- a/drivers/tty/serial/mvebu-uart.c
> +++ b/drivers/tty/serial/mvebu-uart.c
> @@ -470,14 +470,14 @@ static void mvebu_uart_shutdown(struct uart_port *port)
>  	}
>  }
>  
> -static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
> +static unsigned int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
>  {
>  	unsigned int d_divisor, m_divisor;
>  	unsigned long flags;
>  	u32 brdv, osamp;
>  
>  	if (!port->uartclk)
> -		return -EOPNOTSUPP;
> +		return 0;
>  
>  	/*
>  	 * The baudrate is derived from the UART clock thanks to divisors:
> @@ -548,7 +548,7 @@ static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
>  			(m_divisor << 16) | (m_divisor << 24);
>  	writel(osamp, port->membase + UART_OSAMP);
>  
> -	return 0;
> +	return DIV_ROUND_CLOSEST(port->uartclk, d_divisor * m_divisor);
>  }
>  
>  static void mvebu_uart_set_termios(struct uart_port *port,
> @@ -587,15 +587,11 @@ static void mvebu_uart_set_termios(struct uart_port *port,
>  	max_baud = port->uartclk / 80;
>  
>  	baud = uart_get_baud_rate(port, termios, old, min_baud, max_baud);
> -	if (mvebu_uart_baud_rate_set(port, baud)) {
> -		/* No clock available, baudrate cannot be changed */
> -		if (old)
> -			baud = uart_get_baud_rate(port, old, NULL,
> -						  min_baud, max_baud);
> -	} else {
> -		tty_termios_encode_baud_rate(termios, baud, baud);
> -		uart_update_timeout(port, termios->c_cflag, baud);
> -	}
> +	baud = mvebu_uart_baud_rate_set(port, baud);
> +
> +	/* In case baudrate cannot be changed, report previous old value */
> +	if (baud == 0 && old)
> +		baud = tty_termios_baud_rate(old);
>  
>  	/* Only the following flag changes are supported */
>  	if (old) {
> @@ -606,6 +602,11 @@ static void mvebu_uart_set_termios(struct uart_port *port,
>  		termios->c_cflag |= CS8;
>  	}
>  
> +	if (baud != 0) {
> +		tty_termios_encode_baud_rate(termios, baud, baud);
> +		uart_update_timeout(port, termios->c_cflag, baud);
> +	}
> +
>  	spin_unlock_irqrestore(&port->lock, flags);
>  }
>  
>