linux-kernel - Re: [PATCH v3 6/6] tty: serial: 8250: Add support for MOXA PCIe boards to switch interface between RS422/RS485

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Message-ID: <f49feb43-e255-43bb-4271-8a13db2859fc@linux.intel.com>
Date:   Mon, 23 Oct 2023 12:25:18 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Crescent CY Hsieh <crescentcy.hsieh@...a.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-serial <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v3 6/6] tty: serial: 8250: Add support for MOXA PCIe
 boards to switch interface between RS422/RS485

On Wed, 18 Oct 2023, Crescent CY Hsieh wrote:

> MOXA PCIe boards have 4 serial interfaces and don't require additional
> stuff to switch between interfaces:
> 
> - RS232
> - RS422
> - RS485_2W (half-duplex)
> - RS485_4W (full-duplex)
> 
> By using ioctl command "TIOCRS485", it can switch between default
> interface and RS485 if supported.
> 
> That means, for RS422/RS485 board, it can switch between RS422 and
> RS485 by setting the flags within struct serial_rs485.
> 
> However, for the RS232/RS422/RS485 board, it can only switch between
> RS232 and RS485, there's no flag for switching interface into RS422.
> 
> This patch uses "SER_RS485_TERMINATE_BUS" to represent RS422 as a
> workaround solution:
> 
> - RS232                   = (no flags are set)
> - RS422                   = SER_RS485_ENABLED | SER_RS485_TERMINATE_BUS
> - RS485_2W (half-duplex)  = SER_RS485_ENABLED
> - RS485_4W (full-duplex)  = SER_RS485_ENABLED | SER_RS485_RX_DURING_TX
> 
> Signed-off-by: Crescent CY Hsieh <crescentcy.hsieh@...a.com>
> ---
>  drivers/tty/serial/8250/8250_pci.c | 58 ++++++++++++++++++++++++++++++
>  1 file changed, 58 insertions(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
> index 29a28e72b..098ac466b 100644
> --- a/drivers/tty/serial/8250/8250_pci.c
> +++ b/drivers/tty/serial/8250/8250_pci.c
> @@ -1974,6 +1974,10 @@ pci_sunix_setup(struct serial_private *priv,
>  #define MOXA_RS485_2W	0x0F
>  #define MOXA_UIR_OFFSET	0x04
>  
> +static const struct serial_rs485 pci_moxa_rs485_supported = {
> +	.flags = SER_RS485_ENABLED | SER_RS485_RX_DURING_TX | SER_RS485_TERMINATE_BUS,

As recently discussed on linux-serial list, one of the RTS flags should be
enabled (the one the HW uses even if it's not configurable).

> +};
> +
>  static bool pci_moxa_is_mini_pcie(unsigned short device)
>  {
>  	if (device == PCI_DEVICE_ID_MOXA_CP102N	||
> @@ -2024,6 +2028,46 @@ static int pci_moxa_set_interface(const struct pci_dev *dev,
>  	return 0;
>  }
>  
> +/*
> + * MOXA PCIe boards support switching the serial interface using the ioctl
> + * command "TIOCSRS485", but there is currently no dedicated flag for switching
> + * to RS422. As a workaround, we utilize the "SER_RS485_TERMINATE_BUS" flag to
> + * represent RS422.
> + *
> + *	RS232			= (no flags are set)
> + *	RS422			= SER_RS485_ENABLED | SER_RS485_TERMINATE_BUS
> + *	RS485_2W (half-duplex)	= SER_RS485_ENABLED
> + *	RS485_4W (full-duplex)	= SER_RS485_ENABLED | SER_RS485_RX_DURING_TX
> + */
> +static int pci_moxa_rs485_config(struct uart_port *port,
> +				 struct ktermios *termios,
> +				 struct serial_rs485 *rs485)
> +{
> +	struct pci_dev *dev = to_pci_dev(port->dev);
> +	unsigned short device = dev->device;
> +	u8 mode = MOXA_RS232;
> +
> +	if (rs485->flags & SER_RS485_ENABLED) {
> +		if (rs485->flags & SER_RS485_TERMINATE_BUS) {
> +			mode = MOXA_RS422;
> +		} else {
> +			if (rs485->flags & SER_RS485_RX_DURING_TX)
> +				mode = MOXA_RS485_4W;
> +			else
> +				mode = MOXA_RS485_2W;
> +		}
> +	} else {
> +		/*
> +		 * RS232 is not supported for MOXA PCIe boards with device IDs
> +		 * matching the pattern 0x*3**.
> +		 */
> +		if (pci_moxa_match_second_digit(device, 0x0300))
> +			return -EOPNOTSUPP;

This is not the correct error code I think. Maybe return -ENXIO instead.

> +	}
> +
> +	return pci_moxa_set_interface(dev, port->port_id, mode);
> +}
> +
>  static int pci_moxa_init(struct pci_dev *dev)
>  {
>  	unsigned short device = dev->device;
> @@ -2063,9 +2107,23 @@ pci_moxa_setup(struct serial_private *priv,
>  		const struct pciserial_board *board,
>  		struct uart_8250_port *port, int idx)
>  {
> +	struct pci_dev *dev = priv->dev;
> +	unsigned short device = dev->device;
>  	unsigned int bar = FL_GET_BASE(board->flags);
>  	int offset;
>  
> +	/*
> +	 * For the device IDs of MOXA PCIe boards match the pattern 0x*1** and 0x*3**,
> +	 * these boards support switching interface between RS422/RS485 using TIOCSRS485.
> +	 */
> +	if (pci_moxa_match_second_digit(device, 0x0100) ||
> +	    pci_moxa_match_second_digit(device, 0x0300)) {

As mentioned in the other patch, all these literals must be named.

> +		port->port.rs485_config = pci_moxa_rs485_config;
> +		port->port.rs485_supported = pci_moxa_rs485_supported;
> +
> +		if (pci_moxa_match_second_digit(device, 0x0300))
> +			port->port.rs485.flags |= SER_RS485_ENABLED | SER_RS485_TERMINATE_BUS;
> +	}
>  	if (board->num_ports == 4 && idx == 3)
>  		offset = 7 * board->uart_offset;
>  	else
> 

-- 
 i.