linux-kernel - Re: [PATCH v2 2/3] tty: Implement default fallback serial8250_rs485

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Date:	Sat, 7 Nov 2015 07:29:03 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	"Matwey V. Kornilov" <matwey@....msu.ru>
Cc:	gregkh@...uxfoundation.org, jslaby@...e.com,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	matwey.kornilov@...il.com
Subject: Re: [PATCH v2 2/3] tty: Implement default fallback
 serial8250_rs485_config

Hi Matwey,

On 11/07/2015 05:09 AM, Matwey V. Kornilov wrote:
> When 8250 driver doesn't have its own hardware RS485 support and doesn't
> want to override rs485_config callback, then default
> serial8250_rs485_config is used. It just stores supplied by user-space
> config.
> 
> Signed-off-by: Matwey V. Kornilov <matwey@....msu.ru>
> ---
>  drivers/tty/serial/8250/8250_core.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 3912646..8f292da 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -395,6 +395,12 @@ static void serial8250_release_rsa_resource(struct uart_8250_port *up)
>  	}
>  }
>  #endif
> +static int serial8250_rs485_config(struct uart_port *port,
> +				struct serial_rs485 *rs485)
> +{
> +	port->rs485 = *rs485;
> +	return 0;
> +}
>  
>  static const struct uart_ops *base_ops;
>  static struct uart_ops univ8250_port_ops;
> @@ -990,6 +996,10 @@ int serial8250_register_8250_port(struct uart_8250_port *up)
>  		uart->port.rs485	= up->port.rs485;
>  		uart->dma		= up->dma;
>  
> +		/* Use software RS485 support when hardware one is not available */
> +		if (!(uart->capabilities & UART_CAP_HW485) && !uart->port.rs485_config)
> +			uart->port.rs485_config = serial8250_rs485_config;

To setup a default 8250 port function,
1. define the default 8250 port function in 8250/8250_port.c
2. add the port function to the dispatch table (serial8250_pops)
3. add a test for 8250 sub-driver override in serial8250_register_8250_port()
   Eg.,

		if (up->port.rs485_config)
			uart->port.rs485_config = up->port.rs485_config;

Regards,
Peter Hurley

>  		/* Take tx_loadsz from fifosize if it wasn't set separately */
>  		if (uart->port.fifosize && !uart->tx_loadsz)
>  			uart->tx_loadsz = uart->port.fifosize;
> 

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