Add CTS/RTS gpio support to STM32 UART

From: Manivannan Sadhasivam <[email protected]>

Document the use of CTS/RTS gpios for flow control in STM32 UART controller. These properties can be used instead of 'st,hw-flow-ctrl' for making use of any gpio pins for flow control instead of dedicated pins. It should be noted that both CTS/RTS and 'st,hw-flow-ctrl' properties cannot co-exist in a design.

Reviewed-by Andy Shevchenko <[email protected]>

Signed-off-by Manivannan Sadhasivam <[email protected]>

---
 .../devicetree/bindings/serial/st,stm32-uart.yaml  | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

From: Manivannan Sadhasivam <[email protected]>

Document the use of CTS/RTS gpios for flow control in STM32 UART controller. These properties can be used instead of 'st,hw-flow-ctrl' for making use of any gpio pins for flow control instead of dedicated pins. It should be noted that both CTS/RTS and 'st,hw-flow-ctrl' properties cannot co-exist in a design.

Reviewed-by Andy Shevchenko <[email protected]>

Signed-off-by Manivannan Sadhasivam <[email protected]>

Hi Mani,

Quoted 16 lines · On Mon, Apr 20, 2020 at 7:02 PM <[email protected]> wrote:

From: Manivannan Sadhasivam <[email protected]>

Document the use of CTS/RTS gpios for flow control in STM32 UART controller. These properties can be used instead of 'st,hw-flow-ctrl' for making use of any gpio pins for flow control instead of dedicated pins. It should be noted that both CTS/RTS and 'st,hw-flow-ctrl' properties cannot co-exist in a design.

Reviewed-by Andy Shevchenko <[email protected]>

Signed-off-by Manivannan Sadhasivam <[email protected]>

Documentation/devicetree/bindings/serial/st,stm32-uart.yaml +0 -0

@@ -55,6 +61,14 @@ properties:
    linux,rs485-enabled-at-boot-time: true
    rs485-rx-during-tx: true
 

Documentation/devicetree/bindings/serial/st,stm32-uart.yaml properties: · line 66

Quoted 3 lines

Documentation/devicetree/bindings/serial/st,stm32-uart.yaml +3 -0

+if:
+  required:
+    - st,hw-flow-ctrl

Perhaps "st,hw-flow-ctrl" should be deprecated, in favor of the standard "uart-has-rtscts" property?
Of course the driver needs to gain support for the latter first.

Documentation/devicetree/bindings/serial/st,stm32-uart.yaml properties: · line 74

Quoted 9 lines

Documentation/devicetree/bindings/serial/st,stm32-uart.yaml +5 -0

+then:
+  properties:
+    cts-gpios: false
+    rts-gpios: false
+
  required:
    - compatible
    - reg

Gr{oetje,eeting}s,

Geert

From: Manivannan Sadhasivam <[email protected]>

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.

Reviewed-by Andy Shevchenko <[email protected]>

Signed-off-by Manivannan Sadhasivam <[email protected]>

---
 drivers/tty/serial/Kconfig       |  1 +
 drivers/tty/serial/stm32-usart.c | 53 ++++++++++++++++++++++++++++++--
 drivers/tty/serial/stm32-usart.h |  1 +
 3 files changed, 53 insertions(+), 2 deletions(-)

drivers/tty/serial/Kconfig +1 -0

index 0aea76cd67ff..e7a6f2130684 100644
@@ -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.

drivers/tty/serial/stm32-usart.c +51 -2

index 5e93e8d40f59..17c2f3276888 100644
@@ -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);
+	unsigned int ret;
+
 	/* 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)
+{
+	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,

@@ -960,10 +988,31 @@ static int stm32_init_port(struct stm32_port *stm32port,
 
 	stm32port->port.uartclk = clk_get_rate(stm32port->clk);
 	if (!stm32port->port.uartclk) {
-		clk_disable_unprepare(stm32port->clk);
 		ret = -EINVAL;
+		goto err_clk;
+	}
+
+	stm32port->gpios = mctrl_gpio_init(&stm32port->port, 0);
+	if (IS_ERR(stm32port->gpios)) {
+		ret = PTR_ERR(stm32port->gpios);
+		goto err_clk;
 	}
 
+	/* 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");
+			ret = -EINVAL;
+			goto err_clk;
+		}
+	}
+
+	return ret;
+
+err_clk:
+	clk_disable_unprepare(stm32port->clk);
+
 	return ret;
 }
 

drivers/tty/serial/stm32-usart.h +0 -0

index db8bf0d4982d..d4c916e78d40 100644

From: Manivannan Sadhasivam <[email protected]>

Hello,

This patchset adds CTS/RTS gpio support to STM32 UART controller. Eventhough the UART controller supports using dedicated CTS/RTS gpios, sometimes we need to use different set of gpios for flow control.

This is necessary for the upcoming STM32MP1 based board called Stinger96 IoT-Box. On that board, a bluetooth chip is connected to one of the UART controller but the CTS/RTS lines got swapped mistakenly. So this patchset serves as a workaround for that hardware bug and also supports the usecase of using any gpio for CTS/RTS functionality. As per the sugggestion provided by Andy for v1, I've now switched to mctrl_gpio driver.

This patchset has been validated with Stinger96 IoT-Box connected to Murata WiFi-BT combo chip.

Thanks,
Mani

Changes in v3:

* Added Andy's reviewed-by tag
* Fixed minor issues spotted by Fabrice

Changes in v2:

As per the review by Andy:

* Switched to mctrl_gpio driver instead of using custom CTS/RTS implementation
* Removed the use of software flow control terminology.

Manivannan Sadhasivam (2):
dt-bindings: serial: Document CTS/RTS gpios in STM32 UART
tty: serial: Add modem control gpio support for STM32 UART

 .../bindings/serial/st,stm32-uart.yaml        | 14 +++++
 drivers/tty/serial/Kconfig                    |  1 +
 drivers/tty/serial/stm32-usart.c              | 53 ++++++++++++++++++-
 drivers/tty/serial/stm32-usart.h              |  1 +
 4 files changed, 67 insertions(+), 2 deletions(-)

Signature · 1 line

2.17.1

Hi Greg,

Quoted 15 lines · On Mon, Apr 20, 2020 at 10:32:02PM +0530, [email protected] wrote:

From: Manivannan Sadhasivam <[email protected]>

Hello,

This patchset adds CTS/RTS gpio support to STM32 UART controller. Eventhough the UART controller supports using dedicated CTS/RTS gpios, sometimes we need to use different set of gpios for flow control.

This is necessary for the upcoming STM32MP1 based board called Stinger96 IoT-Box. On that board, a bluetooth chip is connected to one of the UART controller but the CTS/RTS lines got swapped mistakenly. So this patchset serves as a workaround for that hardware bug and also supports the usecase of using any gpio for CTS/RTS functionality. As per the sugggestion provided by Andy for v1, I've now switched to mctrl_gpio driver.

Quoted 3 lines

This patchset has been validated with Stinger96 IoT-Box connected to Murata WiFi-BT combo chip.

Are you planning to take this series for 5.8?