serial: stm32: add support for RS485 hardware control mode

Implement Driver Enable signal (DE) to activate the transmission mode
of the external transceiver.

Signed-off-by: Yves Coppeaux <[e-mail]>
Signed-off-by: Bich Hemon <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/stm32-usart.c

···
 	writel_relaxed(val, port->membase + reg);
 }
 
+static void stm32_config_reg_rs485(u32 *cr1, u32 *cr3, u32 delay_ADE,
+				   u32 delay_DDE, u32 baud)
+{
+	u32 rs485_deat_dedt;
+	u32 rs485_deat_dedt_max = (USART_CR1_DEAT_MASK >> USART_CR1_DEAT_SHIFT);
+	bool over8;
+
+	*cr3 |= USART_CR3_DEM;
+	over8 = *cr1 & USART_CR1_OVER8;
+
+	if (over8)
+		rs485_deat_dedt = delay_ADE * baud * 8;
+	else
+		rs485_deat_dedt = delay_ADE * baud * 16;
+
+	rs485_deat_dedt = DIV_ROUND_CLOSEST(rs485_deat_dedt, 1000);
+	rs485_deat_dedt = rs485_deat_dedt > rs485_deat_dedt_max ?
+			  rs485_deat_dedt_max : rs485_deat_dedt;
+	rs485_deat_dedt = (rs485_deat_dedt << USART_CR1_DEAT_SHIFT) &
+			   USART_CR1_DEAT_MASK;
+	*cr1 |= rs485_deat_dedt;
+
+	if (over8)
+		rs485_deat_dedt = delay_DDE * baud * 8;
+	else
+		rs485_deat_dedt = delay_DDE * baud * 16;
+
+	rs485_deat_dedt = DIV_ROUND_CLOSEST(rs485_deat_dedt, 1000);
+	rs485_deat_dedt = rs485_deat_dedt > rs485_deat_dedt_max ?
+			  rs485_deat_dedt_max : rs485_deat_dedt;
+	rs485_deat_dedt = (rs485_deat_dedt << USART_CR1_DEDT_SHIFT) &
+			   USART_CR1_DEDT_MASK;
+	*cr1 |= rs485_deat_dedt;
+}
+
+static int stm32_config_rs485(struct uart_port *port,
+			      struct serial_rs485 *rs485conf)
+{
+	struct stm32_port *stm32_port = to_stm32_port(port);
+	struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
+	struct stm32_usart_config *cfg = &stm32_port->info->cfg;
+	u32 usartdiv, baud, cr1, cr3;
+	bool over8;
+	unsigned long flags;
+
+	spin_lock_irqsave(&port->lock, flags);
+	stm32_clr_bits(port, ofs->cr1, BIT(cfg->uart_enable_bit));
+
+	port->rs485 = *rs485conf;
+
+	rs485conf->flags |= SER_RS485_RX_DURING_TX;
+
+	if (rs485conf->flags & SER_RS485_ENABLED) {
+		cr1 = readl_relaxed(port->membase + ofs->cr1);
+		cr3 = readl_relaxed(port->membase + ofs->cr3);
+		usartdiv = readl_relaxed(port->membase + ofs->brr);
+		usartdiv = usartdiv & GENMASK(15, 0);
+		over8 = cr1 & USART_CR1_OVER8;
+
+		if (over8)
+			usartdiv = usartdiv | (usartdiv & GENMASK(4, 0))
+				   << USART_BRR_04_R_SHIFT;
+
+		baud = DIV_ROUND_CLOSEST(port->uartclk, usartdiv);
+		stm32_config_reg_rs485(&cr1, &cr3,
+				       rs485conf->delay_rts_before_send,
+				       rs485conf->delay_rts_after_send, baud);
+
+		if (rs485conf->flags & SER_RS485_RTS_ON_SEND) {
+			cr3 &= ~USART_CR3_DEP;
+			rs485conf->flags &= ~SER_RS485_RTS_AFTER_SEND;
+		} else {
+			cr3 |= USART_CR3_DEP;
+			rs485conf->flags |= SER_RS485_RTS_AFTER_SEND;
+		}
+
+		writel_relaxed(cr3, port->membase + ofs->cr3);
+		writel_relaxed(cr1, port->membase + ofs->cr1);
+	} else {
+		stm32_clr_bits(port, ofs->cr3, USART_CR3_DEM | USART_CR3_DEP);
+		stm32_clr_bits(port, ofs->cr1,
+			       USART_CR1_DEDT_MASK | USART_CR1_DEAT_MASK);
+	}
+
+	stm32_set_bits(port, ofs->cr1, BIT(cfg->uart_enable_bit));
+	spin_unlock_irqrestore(&port->lock, flags);
+
+	return 0;
+}
+
+static int stm32_init_rs485(struct uart_port *port,
+			    struct platform_device *pdev)
+{
+	struct serial_rs485 *rs485conf = &port->rs485;
+
+	rs485conf->flags = 0;
+	rs485conf->delay_rts_before_send = 0;
+	rs485conf->delay_rts_after_send = 0;
+
+	if (!pdev->dev.of_node)
+		return -ENODEV;
+
+	uart_get_rs485_mode(&pdev->dev, rs485conf);
+
+	return 0;
+}
+
 static int stm32_pending_rx(struct uart_port *port, u32 *sr, int *last_res,
 			    bool threaded)
 {
···
 	struct stm32_port *stm32_port = to_stm32_port(port);
 	struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
 	struct stm32_usart_config *cfg = &stm32_port->info->cfg;
+	struct serial_rs485 *rs485conf = &port->rs485;
 	unsigned int baud;
 	u32 usartdiv, mantissa, fraction, oversampling;
 	tcflag_t cflag = termios->c_cflag;
···
 	writel_relaxed(0, port->membase + ofs->cr1);
 
 	cr1 = USART_CR1_TE | USART_CR1_RE | USART_CR1_RXNEIE;
-	cr1 |= BIT(cfg->uart_enable_bit);
+
 	if (stm32_port->fifoen)
 		cr1 |= USART_CR1_FIFOEN;
 	cr2 = 0;
···
 	 */
 	if (usartdiv < 16) {
 		oversampling = 8;
+		cr1 |= USART_CR1_OVER8;
 		stm32_set_bits(port, ofs->cr1, USART_CR1_OVER8);
 	} else {
 		oversampling = 16;
+		cr1 &= ~USART_CR1_OVER8;
 		stm32_clr_bits(port, ofs->cr1, USART_CR1_OVER8);
 	}
 
···
 	if (stm32_port->rx_ch)
 		cr3 |= USART_CR3_DMAR;
 
+	if (rs485conf->flags & SER_RS485_ENABLED) {
+		stm32_config_reg_rs485(&cr1, &cr3,
+				       rs485conf->delay_rts_before_send,
+				       rs485conf->delay_rts_after_send, baud);
+		if (rs485conf->flags & SER_RS485_RTS_ON_SEND) {
+			cr3 &= ~USART_CR3_DEP;
+			rs485conf->flags &= ~SER_RS485_RTS_AFTER_SEND;
+		} else {
+			cr3 |= USART_CR3_DEP;
+			rs485conf->flags |= SER_RS485_RTS_AFTER_SEND;
+		}
+
+	} else {
+		cr3 &= ~(USART_CR3_DEM | USART_CR3_DEP);
+		cr1 &= ~(USART_CR1_DEDT_MASK | USART_CR1_DEAT_MASK);
+	}
+
 	writel_relaxed(cr3, port->membase + ofs->cr3);
 	writel_relaxed(cr2, port->membase + ofs->cr2);
 	writel_relaxed(cr1, port->membase + ofs->cr1);
 
+	stm32_set_bits(port, ofs->cr1, BIT(cfg->uart_enable_bit));
 	spin_unlock_irqrestore(&port->lock, flags);
 }
 

drivers/tty/serial/stm32-usart.h

···
 #define USART_BRR_DIV_F_MASK	GENMASK(3, 0)
 #define USART_BRR_DIV_M_MASK	GENMASK(15, 4)
 #define USART_BRR_DIV_M_SHIFT	4
+#define USART_BRR_04_R_SHIFT	1
 
 /* USART_CR1 */
 #define USART_CR1_SBK		BIT(0)
···
 #define USART_CR1_M1		BIT(28)		/* F7 */
 #define USART_CR1_IE_MASK	(GENMASK(8, 4) | BIT(14) | BIT(26) | BIT(27))
 #define USART_CR1_FIFOEN	BIT(29)		/* H7 */
+#define USART_CR1_DEAT_SHIFT 21
+#define USART_CR1_DEDT_SHIFT 16
 
 /* USART_CR2 */
 #define USART_CR2_ADD_MASK	GENMASK(3, 0)	/* F4 */