[PATCH 2/2] serial: stm32: add support for RS485 hardware control mode

From: Bich HEMON
Date: Wed Feb 28 2018 - 05:57:10 EST

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

Signed-off-by: Yves Coppeaux <yves.coppeaux@xxxxxx>
Signed-off-by: Bich Hemon <bich.hemon@xxxxxx>
---
drivers/tty/serial/stm32-usart.c | 134 ++++++++++++++++++++++++++++++++++++++-
drivers/tty/serial/stm32-usart.h | 3 +
2 files changed, 136 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 5c85cbc..6d34472 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -62,6 +62,113 @@ static void stm32_clr_bits(struct uart_port *port, u32 reg, u32 bits)
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)
{
@@ -498,6 +605,7 @@ static void stm32_set_termios(struct uart_port *port, struct ktermios *termios,
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;
@@ -515,7 +623,7 @@ static void stm32_set_termios(struct uart_port *port, struct ktermios *termios,
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;
@@ -553,9 +661,11 @@ static void stm32_set_termios(struct uart_port *port, struct ktermios *termios,
*/
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);
}

@@ -592,10 +702,28 @@ static void stm32_set_termios(struct uart_port *port, struct ktermios *termios,
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);
}

@@ -681,6 +809,10 @@ static int stm32_init_port(struct stm32_port *stm32port,
port->ops = &stm32_uart_ops;
port->dev = &pdev->dev;
port->irq = platform_get_irq_byname(pdev, "event");
+
+ port->rs485_config = stm32_config_rs485;
+ stm32_init_rs485(port, pdev);
+
stm32port->wakeirq = platform_get_irq_byname(pdev, "wakeup");
stm32port->fifoen = stm32port->info->cfg.has_fifo;

diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
index 2294d0f..6f294e2 100644
--- a/drivers/tty/serial/stm32-usart.h
+++ b/drivers/tty/serial/stm32-usart.h
@@ -135,6 +135,7 @@ struct stm32_usart_info stm32h7_info = {
#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)
@@ -162,6 +163,8 @@ struct stm32_usart_info stm32h7_info = {
#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 */
--
1.9.1

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