Re: [PATCH v2 1/2] tty: serial: Add modem control gpio support for STM32 UART

[Fabrice Gasnier]

On 4/16/20 7:57 PM, mani@xxxxxxxxxx wrote:
> From: Manivannan Sadhasivam <mani@xxxxxxxxxx>
> 
> STM32 UART controllers have the built in modem control support using
> dedicated gpios which can be enabled using 'st,hw-flow-ctrl' flag in DT.
> But there might be cases where the board design need to use different
> gpios for modem control.
> 
> For supporting such cases, this commit adds modem control gpio support
> to STM32 UART controller using mctrl_gpio driver.
> 
> Signed-off-by: Manivannan Sadhasivam <mani@xxxxxxxxxx>
> ---
>  drivers/tty/serial/Kconfig       |  1 +
>  drivers/tty/serial/stm32-usart.c | 43 +++++++++++++++++++++++++++++++-
>  drivers/tty/serial/stm32-usart.h |  1 +
>  3 files changed, 44 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index 0aea76cd67ff..e7a6f2130684 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -1462,6 +1462,7 @@ config SERIAL_STM32
>  	tristate "STMicroelectronics STM32 serial port support"
>  	select SERIAL_CORE
>  	depends on ARCH_STM32 || COMPILE_TEST
> +	select SERIAL_MCTRL_GPIO if GPIOLIB
>  	help
>  	  This driver is for the on-chip Serial Controller on
>  	  STMicroelectronics STM32 MCUs.
> diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
> index 5e93e8d40f59..026982259714 100644
> --- a/drivers/tty/serial/stm32-usart.c
> +++ b/drivers/tty/serial/stm32-usart.c
> @@ -31,6 +31,7 @@
>  #include <linux/tty_flip.h>
>  #include <linux/tty.h>
>  
> +#include "serial_mctrl_gpio.h"
>  #include "stm32-usart.h"
>  
>  static void stm32_stop_tx(struct uart_port *port);
> @@ -510,12 +511,29 @@ static void stm32_set_mctrl(struct uart_port *port, unsigned int mctrl)
>  		stm32_set_bits(port, ofs->cr3, USART_CR3_RTSE);
>  	else
>  		stm32_clr_bits(port, ofs->cr3, USART_CR3_RTSE);
> +
> +	mctrl_gpio_set(stm32_port->gpios, mctrl);
>  }
>  
>  static unsigned int stm32_get_mctrl(struct uart_port *port)
>  {
> +	struct stm32_port *stm32_port = to_stm32_port(port);
> +	int ret;

Hi Mani,

Please find few minor remarks and a question from my side.

'ret' could be an unsigned int

> +
>  	/* This routine is used to get signals of: DCD, DSR, RI, and CTS */
> -	return TIOCM_CAR | TIOCM_DSR | TIOCM_CTS;
> +	ret = TIOCM_CAR | TIOCM_DSR | TIOCM_CTS;
> +
> +	return mctrl_gpio_get(stm32_port->gpios, &ret);
> +}
> +
> +static void stm32_enable_ms(struct uart_port *port)
> +{

Just a question here: purpose of your patch is to handle the gpio case.
So you may get modem control interrupts from gpios with this patch.

In other drivers, I can see the implementation checks gpio usage (like
in atmel_serial). When there's no gpio, the corresponding interrupt at
the serial controller level is enabled, e.g. :

	if (!mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_CTS))
		ier |= ...

Do you need modem control interrupts in your case ?

In case the Stinger96 board signals gets fixed in a future revision,
would it be needed to enable modem control interrupts in the USART
controller ?

> +	mctrl_gpio_enable_ms(to_stm32_port(port)->gpios);
> +}
> +
> +static void stm32_disable_ms(struct uart_port *port)
> +{
> +	mctrl_gpio_disable_ms(to_stm32_port(port)->gpios);
>  }
>  
>  /* Transmit stop */
> @@ -626,6 +644,9 @@ static void stm32_shutdown(struct uart_port *port)
>  	u32 val, isr;
>  	int ret;
>  
> +	/* Disable modem control interrupts */
> +	stm32_disable_ms(port);
> +
>  	val = USART_CR1_TXEIE | USART_CR1_TE;
>  	val |= stm32_port->cr1_irq | USART_CR1_RE;
>  	val |= BIT(cfg->uart_enable_bit);
> @@ -764,6 +785,12 @@ static void stm32_set_termios(struct uart_port *port, struct ktermios *termios,
>  		cr3 |= USART_CR3_CTSE | USART_CR3_RTSE;
>  	}
>  
> +	/* Handle modem control interrupts */
> +	if (UART_ENABLE_MS(port, termios->c_cflag))
> +		stm32_enable_ms(port);
> +	else
> +		stm32_disable_ms(port);
> +
>  	usartdiv = DIV_ROUND_CLOSEST(port->uartclk, baud);
>  
>  	/*
> @@ -898,6 +925,7 @@ static const struct uart_ops stm32_uart_ops = {
>  	.throttle	= stm32_throttle,
>  	.unthrottle	= stm32_unthrottle,
>  	.stop_rx	= stm32_stop_rx,
> +	.enable_ms	= stm32_enable_ms,
>  	.break_ctl	= stm32_break_ctl,
>  	.startup	= stm32_startup,
>  	.shutdown	= stm32_shutdown,
> @@ -964,6 +992,19 @@ static int stm32_init_port(struct stm32_port *stm32port,
>  		ret = -EINVAL;

return -EINVAL;

>  	}
>  
> +	stm32port->gpios = mctrl_gpio_init(&stm32port->port, 0);
> +	if (IS_ERR(stm32port->gpios))

Please add error path: add a clk_disable_unprepare() here, before the
return.

> +		return PTR_ERR(stm32port->gpios);
> +
> +	/* Both CTS/RTS gpios and "st,hw-flow-ctrl" should not be specified */
> +	if (stm32port->hw_flow_control) {
> +		if (mctrl_gpio_to_gpiod(stm32port->gpios, UART_GPIO_CTS) ||
> +		    mctrl_gpio_to_gpiod(stm32port->gpios, UART_GPIO_RTS)) {
> +			dev_err(&pdev->dev, "Conflicting RTS/CTS config\n");

same here

Best Regards,
Thanks,
Fabrice

> +			return -EINVAL;
> +		}
> +	}
> +
>  	return ret;
>  }
>  
> diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
> index db8bf0d4982d..d4c916e78d40 100644
> --- a/drivers/tty/serial/stm32-usart.h
> +++ b/drivers/tty/serial/stm32-usart.h
> @@ -274,6 +274,7 @@ struct stm32_port {
>  	bool fifoen;
>  	int wakeirq;
>  	int rdr_mask;		/* receive data register mask */
> +	struct mctrl_gpios *gpios; /* modem control gpios */
>  };
>  
>  static struct stm32_port stm32_ports[STM32_MAX_PORTS];
>