linux-kernel - Re: [RESEND PATCH v4 1/3] usb: serial: Add MaxLinear/Exar USB to Serial driver

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Message-ID: <20200701130924.GE3334@localhost>
Date:   Wed, 1 Jul 2020 15:09:24 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Manivannan Sadhasivam <mani@...nel.org>
Cc:     johan@...nel.org, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        patong.mxl@...il.com, linus.walleij@...aro.org,
        mchehab+huawei@...nel.org
Subject: Re: [RESEND PATCH v4 1/3] usb: serial: Add MaxLinear/Exar USB to
 Serial driver

On Sun, Jun 07, 2020 at 09:53:48PM +0530, Manivannan Sadhasivam wrote:
> Add support for MaxLinear/Exar USB to Serial converters. This driver
> only supports XR21V141X series but it can be extended to other series
> from Exar as well in future.
> 
> This driver is inspired from the initial one submitted by Patong Yang:
> 
> https://patchwork.kernel.org/patch/10543261/
> 
> While the initial driver was a custom tty USB driver exposing whole
> new serial interface ttyXRUSBn, this version is completely based on USB
> serial core thus exposing the interfaces as ttyUSBn. This will avoid
> the overhead of exposing a new USB serial interface which the userspace
> tools are unaware of.
> 
> Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Tested-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> Signed-off-by: Manivannan Sadhasivam <mani@...nel.org>
> ---
>  drivers/usb/serial/Kconfig     |   9 +
>  drivers/usb/serial/Makefile    |   1 +
>  drivers/usb/serial/xr_serial.c | 650 +++++++++++++++++++++++++++++++++
>  3 files changed, 660 insertions(+)
>  create mode 100644 drivers/usb/serial/xr_serial.c

> +static int xr_tiocmset_port(struct usb_serial_port *port,
> +			    unsigned int set, unsigned int clear)
> +{
> +	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
> +	int ret = 0;
> +	u8 gpio_set = 0;
> +	u8 gpio_clr = 0;
> +
> +	/* Modem control pins are active low, so set & clr are swapped */
> +	if (set & TIOCM_RTS)
> +		gpio_clr |= UART_MODE_RTS;
> +	if (set & TIOCM_DTR)
> +		gpio_clr |= UART_MODE_DTR;
> +	if (clear & TIOCM_RTS)
> +		gpio_set |= UART_MODE_RTS;
> +	if (clear & TIOCM_DTR)
> +		gpio_set |= UART_MODE_DTR;
> +
> +	/* Writing '0' to gpio_{set/clr} bits has no effect, so no need to do */
> +	if (gpio_clr) {
> +		ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> +				 port_priv->regs->gpio_clr, gpio_clr);
> +	}
> +
> +	if (gpio_set) {
> +		ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> +				 port_priv->regs->gpio_set, gpio_set);
> +	}
> +
> +	return ret;
> +}
> +
> +static int xr_tiocmset(struct tty_struct *tty,
> +		       unsigned int set, unsigned int clear)
> +{
> +	struct usb_serial_port *port = tty->driver_data;
> +
> +	return xr_tiocmset_port(port, set, clear);
> +}

> +static void xr_dtr_rts(struct usb_serial_port *port, int on)
> +{
> +	if (on)
> +		xr_tiocmset_port(port, TIOCM_DTR | TIOCM_RTS, 0);
> +	else
> +		xr_tiocmset_port(port, 0, TIOCM_DTR | TIOCM_RTS);
> +}

By the way, don't you need to configure the DTR and RTS pins as outputs
for the serial driver as well?

According to the datasheet they are both configured as inputs by default
(or at least RTS is).

In any case, you'll need to reconfigure each pin after they are released
by gpiolib.

Johan