[PATCH V7 2/2] serial: exar: Add RS-485 support for Sealevel XR17V35X based cards

[Matthew Howell <matthew.howell@sealevel.com>]

From: Matthew Howell <matthew.howell@sealevel.com>

Sealevel XR17V35X based cards utilize DTR to control RS-485 Enable, but
the current implementation of 8250_exar uses RTS for the auto-RS485-Enable
mode of the XR17V35X UARTs. This patch implements DTR Auto-RS485 on
Sealevel cards.

Signed-off-by: Matthew Howell <matthew.howell@sealevel.com>
---
V6->V7
Added return check in sealevel_rs485_config()
Fixed misaligned tabbing for UART_EXAR_DLD
Hopefully Alpine threads correctly this time

diff --git a/drivers/tty/serial/8250/8250_exar.c b/drivers/tty/serial/8250/8250_exar.c
index 3886f78ecbbf..03e4162ee131 100644
--- a/drivers/tty/serial/8250/8250_exar.c
+++ b/drivers/tty/serial/8250/8250_exar.c
@@ -78,6 +78,9 @@

 #define UART_EXAR_RS485_DLY(x)	((x) << 4)

+#define UART_EXAR_DLD			0x02 /* Divisor Fractional */
+#define UART_EXAR_DLD_485_POLARITY	0x80 /* RS-485 Enable Signal Polarity */
+
 /*
  * IOT2040 MPIO wiring semantics:
  *
@@ -439,6 +442,45 @@ static int generic_rs485_config(struct uart_port *port, struct ktermios *termios
 	return 0;
 }

+static int sealevel_rs485_config(struct uart_port *port, struct ktermios *termios,
+				struct serial_rs485 *rs485)
+{
+	u8 __iomem *p = port->membase;
+	u8 old_lcr;
+	u8 efr;
+	u8 dld;
+	int ret;
+
+	ret = generic_rs485_config(port, termios, rs485);
+
+	if (ret)
+		return ret;
+
+	if (rs485->flags & SER_RS485_ENABLED) {
+		old_lcr = readb(p + UART_LCR);
+
+		/* Set EFR[4]=1 to enable enhanced feature registers */
+		efr = readb(p + UART_XR_EFR);
+		efr |= UART_EFR_ECB;
+		writeb(efr, p + UART_XR_EFR);
+
+		/* Set MCR to use DTR as Auto-RS485 Enable signal */
+		writeb(UART_MCR_OUT1, p + UART_MCR);
+
+		/* Set LCR[7]=1 to enable access to DLD register */
+		writeb(old_lcr | UART_LCR_DLAB, p + UART_LCR);
+
+		/* Set DLD[7]=1 for inverted RS485 Enable logic */
+		dld = readb(p + UART_EXAR_DLD);
+		dld |= UART_EXAR_DLD_485_POLARITY;
+		writeb(dld, p + UART_EXAR_DLD);
+
+		writeb(old_lcr, p + UART_LCR);
+	}
+
+	return 0;
+}
+
 static const struct serial_rs485 generic_rs485_supported = {
 	.flags = SER_RS485_ENABLED,
 };
@@ -744,6 +786,20 @@ static int __maybe_unused exar_resume(struct device *dev)
 	return 0;
 }

+static int pci_sealevel_setup(struct exar8250 *priv, struct pci_dev *pcidev,
+		   struct uart_8250_port *port, int idx)
+{
+	int ret;
+
+	ret = pci_xr17v35x_setup(priv, pcidev, port, idx);
+	if (ret)
+		return ret;
+
+	port->port.rs485_config = sealevel_rs485_config;
+
+	return 0;
+}
+
 static SIMPLE_DEV_PM_OPS(exar_pci_pm, exar_suspend, exar_resume);

 static const struct exar8250_board pbn_fastcom335_2 = {
@@ -809,6 +865,17 @@ static const struct exar8250_board pbn_exar_XR17V8358 = {
 	.exit		= pci_xr17v35x_exit,
 };

+static const struct exar8250_board pbn_sealevel = {
+	.setup		= pci_sealevel_setup,
+	.exit		= pci_xr17v35x_exit,
+};
+
+static const struct exar8250_board pbn_sealevel_16 = {
+	.num_ports	= 16,
+	.setup		= pci_sealevel_setup,
+	.exit		= pci_xr17v35x_exit,
+};
+
 #define CONNECT_DEVICE(devid, sdevid, bd) {				\
 	PCI_DEVICE_SUB(							\
 		PCI_VENDOR_ID_EXAR,					\
@@ -838,6 +905,15 @@ static const struct exar8250_board pbn_exar_XR17V8358 = {
 		(kernel_ulong_t)&bd			\
 	}

+#define SEALEVEL_DEVICE(devid, bd) {			\
+	PCI_DEVICE_SUB(					\
+		PCI_VENDOR_ID_EXAR,			\
+		PCI_DEVICE_ID_EXAR_##devid,		\
+		PCI_VENDOR_ID_SEALEVEL,			\
+		PCI_ANY_ID), 0, 0,			\
+		(kernel_ulong_t)&bd			\
+	}
+
 static const struct pci_device_id exar_pci_tbl[] = {
 	EXAR_DEVICE(ACCESSIO, COM_2S, pbn_exar_XR17C15x),
 	EXAR_DEVICE(ACCESSIO, COM_4S, pbn_exar_XR17C15x),
@@ -860,6 +936,12 @@ static const struct pci_device_id exar_pci_tbl[] = {
 	CONNECT_DEVICE(XR17C154, UART_4_485, pbn_connect),
 	CONNECT_DEVICE(XR17C158, UART_8_485, pbn_connect),

+	SEALEVEL_DEVICE(XR17V352, pbn_sealevel),
+	SEALEVEL_DEVICE(XR17V354, pbn_sealevel),
+	SEALEVEL_DEVICE(XR17V358, pbn_sealevel),
+	SEALEVEL_DEVICE(XR17V4358, pbn_sealevel_16),
+	SEALEVEL_DEVICE(XR17V8358, pbn_sealevel_16),
+
 	IBM_DEVICE(XR17C152, SATURN_SERIAL_ONE_PORT, pbn_exar_ibm_saturn),

 	/* USRobotics USR298x-OEM PCI Modems */