linux-kernel - Re: [PATCHv2] serial: don't register CIR serial ports

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Message-ID: <55C25DD2.4050707@hurleysoftware.com>
Date:	Wed, 05 Aug 2015 15:02:42 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	"Maciej S. Szmigiero" <mail@...iej.szmigiero.name>,
	linux-serial@...r.kernel.org
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2] serial: don't register CIR serial ports

On 08/05/2015 11:43 AM, Maciej S. Szmigiero wrote:
> CIR type serial ports aren't real serial ports.
> 
> This is just a way to prevent legacy 8250 serial
> driver from probing and eventually binding some
> resources.
> 
> Since in current state such ports aren't providing
> any real functionality and it is not possible
> to change their type via setserial/ioctl(TIOCSSERIAL)
> (due to UPF_FIXED_PORT flag set on them)
> it is simpler and cleaner to not register them at all
> with serial core.


The only thing I think this patch is missing is either a comment
or specific code in serial8250_register_ports() regarding not
adding PORT_8250_CIR-type ports.

Like either:

static void __init
serial8250_register_ports(struct uart_driver *drv, struct device *dev)
{
	int i;

	for (i = 0; i < nr_uarts; i++) {
		struct uart_8250_port *up = &serial8250_ports[i];

+		/* PORT_8250_CIR-type ports must have non-NULL dev */
		if (up->port.dev)
			continue;

		up->port.dev = dev;

or:

static void __init
serial8250_register_ports(struct uart_driver *drv, struct device *dev)
{
	int i;

	for (i = 0; i < nr_uarts; i++) {
		struct uart_8250_port *up = &serial8250_ports[i];

+		if (up->port.type == PORT_8250_CIR)
+			continue;

		if (up->port.dev)
			continue;

		up->port.dev = dev;

Regards,
Peter Hurley

> Print a short message in this case so it is known
> to user what has happened.
> 
> This way checks for PORT_8250_CIR in serial port
> callbacks can be removed too, since they won't
> ever be called.
> 
> Signed-off-by: Maciej Szmigiero <mail@...iej.szmigiero.name>
> ---
> This replaces "serial: don't announce CIR serial ports"
> submission.
> 
> Changes from v1: print message using dev_info()
> 
>  drivers/tty/serial/8250/8250_core.c |   37 +++++++++++++++++------------------
>  1 files changed, 18 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 37fff12..145b0b37 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -2129,9 +2129,6 @@ int serial8250_do_startup(struct uart_port *port)
>  	unsigned char lsr, iir;
>  	int retval;
>  
> -	if (port->type == PORT_8250_CIR)
> -		return -ENODEV;
> -
>  	if (!port->fifosize)
>  		port->fifosize = uart_config[port->type].fifo_size;
>  	if (!up->tx_loadsz)
> @@ -2858,14 +2855,8 @@ static void serial8250_release_port(struct uart_port *port)
>  static int serial8250_request_port(struct uart_port *port)
>  {
>  	struct uart_8250_port *up = up_to_u8250p(port);
> -	int ret;
> -
> -	if (port->type == PORT_8250_CIR)
> -		return -ENODEV;
> -
> -	ret = serial8250_request_std_resource(up);
>  
> -	return ret;
> +	return serial8250_request_std_resource(up);
>  }
>  
>  static int fcr_get_rxtrig_bytes(struct uart_8250_port *up)
> @@ -3013,9 +3004,6 @@ static void serial8250_config_port(struct uart_port *port, int flags)
>  	struct uart_8250_port *up = up_to_u8250p(port);
>  	int ret;
>  
> -	if (port->type == PORT_8250_CIR)
> -		return;
> -
>  	/*
>  	 * Find the region that we can probe for.  This in turn
>  	 * tells us whether we can probe for the type of port.
> @@ -3889,13 +3877,24 @@ int serial8250_register_8250_port(struct uart_8250_port *up)
>  		if (up->dl_write)
>  			uart->dl_write = up->dl_write;
>  
> -		if (serial8250_isa_config != NULL)
> -			serial8250_isa_config(0, &uart->port,
> -					&uart->capabilities);
> +		if (uart->port.type != PORT_8250_CIR) {
> +			if (serial8250_isa_config != NULL)
> +				serial8250_isa_config(0, &uart->port,
> +						&uart->capabilities);
>  
> -		ret = uart_add_one_port(&serial8250_reg, &uart->port);
> -		if (ret == 0)
> -			ret = uart->port.line;
> +			ret = uart_add_one_port(&serial8250_reg,
> +						&uart->port);
> +			if (ret == 0)
> +				ret = uart->port.line;
> +		} else {
> +			dev_info(uart->port.dev,
> +				"skipping CIR port at 0x%lx / 0x%llx, IRQ %d\n",
> +				uart->port.iobase,
> +				(unsigned long long)uart->port.mapbase,
> +				uart->port.irq);
> +
> +			ret = 0;
> +		}
>  	}
>  	mutex_unlock(&serial_mutex);
>  
> 

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