[PATCH v7 tty-next 3/4] serial: 8250_pci1xxxx: Add RS485 support to quad-uart driver

[Kumaravel Thiagarajan]

pci1xxxx uart supports RS485 mode of operation in the hardware with
auto-direction control with configurable delay for releasing RTS after
the transmission. This patch adds support for the RS485 mode.

Co-developed-by: Tharun Kumar P <tharunkumar.pasumarthi@xxxxxxxxxxxxx>
Signed-off-by: Tharun Kumar P <tharunkumar.pasumarthi@xxxxxxxxxxxxx>
Signed-off-by: Kumaravel Thiagarajan <kumaravel.thiagarajan@xxxxxxxxxxxxx>
---
Changes in v7:
- No Change

Changes in v6:
- Modified datatype of delay_in_baud_periods to u64 to avoid overflows

Changes in v5:
- Removed unnecessary assignments
- Corrected styling issues in comments

Changes in v4:
- No Change

Changes in v3:
- Remove flags sanitization in driver which is taken care in core

Changes in v2:
- move pci1xxxx_rs485_config to a separate patch with
  pci1xxxx_rs485_supported.
---
 drivers/tty/serial/8250/8250_pci1xxxx.c | 49 +++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_pci1xxxx.c b/drivers/tty/serial/8250/8250_pci1xxxx.c
index be554e2d884b..9f0da264314a 100644
--- a/drivers/tty/serial/8250/8250_pci1xxxx.c
+++ b/drivers/tty/serial/8250/8250_pci1xxxx.c
@@ -145,6 +145,53 @@ static void pci1xxxx_set_divisor(struct uart_port *port, unsigned int baud,
 	       port->membase + UART_BAUD_CLK_DIVISOR_REG);
 }
 
+static int pci1xxxx_rs485_config(struct uart_port *port,
+				 struct ktermios *termios,
+				 struct serial_rs485 *rs485)
+{
+	u32 clock_div = readl(port->membase + UART_BAUD_CLK_DIVISOR_REG);
+	u64 delay_in_baud_periods;
+	u32 baud_period_in_ns;
+	u32 data = 0;
+
+	/*
+	 * pci1xxxx's uart hardware supports only RTS delay after
+	 * Tx and in units of bit times to a maximum of 15
+	 */
+	if (rs485->flags & SER_RS485_ENABLED) {
+		data = ADCL_CFG_EN | ADCL_CFG_PIN_SEL;
+
+		if (!(rs485->flags & SER_RS485_RTS_ON_SEND))
+			data |= ADCL_CFG_POL_SEL;
+
+		if (rs485->delay_rts_after_send) {
+			baud_period_in_ns =
+				FIELD_GET(BAUD_CLOCK_DIV_INT_MSK, clock_div) *
+				UART_BIT_SAMPLE_CNT;
+			delay_in_baud_periods =
+				rs485->delay_rts_after_send * NSEC_PER_MSEC /
+				baud_period_in_ns;
+			delay_in_baud_periods =
+				min_t(u64, delay_in_baud_periods,
+				      FIELD_MAX(ADCL_CFG_RTS_DELAY_MASK));
+			data |= FIELD_PREP(ADCL_CFG_RTS_DELAY_MASK,
+					   delay_in_baud_periods);
+			rs485->delay_rts_after_send =
+				baud_period_in_ns * delay_in_baud_periods /
+				NSEC_PER_MSEC;
+		}
+	}
+	writel(data, port->membase + ADCL_CFG_REG);
+	return 0;
+}
+
+static const struct serial_rs485 pci1xxxx_rs485_supported = {
+	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND |
+		 SER_RS485_RTS_AFTER_SEND,
+	.delay_rts_after_send = 1,
+	/* Delay RTS before send is not supported */
+};
+
 static int pci1xxxx_setup(struct pci1xxxx_8250 *priv,
 			  struct uart_8250_port *port, int port_idx)
 {
@@ -155,6 +202,8 @@ static int pci1xxxx_setup(struct pci1xxxx_8250 *priv,
 	port->port.set_termios = serial8250_do_set_termios;
 	port->port.get_divisor = pci1xxxx_get_divisor;
 	port->port.set_divisor = pci1xxxx_set_divisor;
+	port->port.rs485_config = pci1xxxx_rs485_config;
+	port->port.rs485_supported = pci1xxxx_rs485_supported;
 
 	ret = serial8250_pci_setup_port(priv->pdev, port, 0, port_idx * 256, 0);
 	if (ret < 0)
-- 
2.25.1