[PATCH v2] tty: serial: 8250: Fix MOXA RS422/RS485 PCIe boards not work by default

[Crescent CY Hsieh]

MOXA PCIe RS422/RS485 boards will not function by default because of the
initial default serial interface of all MOXA PCIe boards is set to
RS232.

This patch fixes the problem above by setting the initial default serial
interface to RS422 for those MOXA RS422/RS485 PCIe boards.

Signed-off-by: Crescent CY Hsieh <crescentcy.hsieh@xxxxxxxx>
Reviewed-by: Jiri Slaby <jirislaby@xxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202312060523.Kmstf65q-lkp@xxxxxxxxx/

---
Changes from v1 to v2:
- Fix issue reported by kernel test robot
	- Replace function return type from u32 to static unsigned int

v1: https://lore.kernel.org/all/20231201074055.259207-1-crescentcy.hsieh@xxxxxxxx/

---
 drivers/tty/serial/8250/8250_pci.c | 58 +++++++++++++++++++++++++++++-
 1 file changed, 57 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
index b2be3783f..42fbbe89e 100644
--- a/drivers/tty/serial/8250/8250_pci.c
+++ b/drivers/tty/serial/8250/8250_pci.c
@@ -19,6 +19,7 @@
 #include <linux/serial_core.h>
 #include <linux/8250_pci.h>
 #include <linux/bitops.h>
+#include <linux/bitfield.h>
 
 #include <asm/byteorder.h>
 #include <asm/io.h>
@@ -1968,6 +1969,20 @@ pci_sunix_setup(struct serial_private *priv,
 
 #define MOXA_GPIO_PIN2	BIT(2)
 
+#define MOXA_RS232	0x00
+#define MOXA_RS422	0x01
+#define MOXA_RS485_4W	0x0B
+#define MOXA_RS485_2W	0x0F
+#define MOXA_UIR_OFFSET	0x04
+#define MOXA_EVEN_RS_MASK	GENMASK(3, 0)
+#define MOXA_ODD_RS_MASK	GENMASK(7, 4)
+
+enum {
+	MOXA_SUPP_RS232 = BIT(0),
+	MOXA_SUPP_RS422 = BIT(1),
+	MOXA_SUPP_RS485 = BIT(2),
+};
+
 static bool pci_moxa_is_mini_pcie(unsigned short device)
 {
 	if (device == PCI_DEVICE_ID_MOXA_CP102N	||
@@ -1981,13 +1996,54 @@ static bool pci_moxa_is_mini_pcie(unsigned short device)
 	return false;
 }
 
+static unsigned int pci_moxa_supported_rs(struct pci_dev *dev)
+{
+	switch (dev->device & 0x0F00) {
+	case 0x0000:
+	case 0x0600:
+		return MOXA_SUPP_RS232;
+	case 0x0100:
+		return MOXA_SUPP_RS232 | MOXA_SUPP_RS422 | MOXA_SUPP_RS485;
+	case 0x0300:
+		return MOXA_SUPP_RS422 | MOXA_SUPP_RS485;
+	}
+	return 0;
+}
+
+static int pci_moxa_set_interface(const struct pci_dev *dev,
+				  unsigned int port_idx,
+				  u8 mode)
+{
+	resource_size_t iobar_addr = pci_resource_start(dev, 2);
+	resource_size_t UIR_addr = iobar_addr + MOXA_UIR_OFFSET + port_idx / 2;
+	u8 val;
+
+	val = inb(UIR_addr);
+
+	if (port_idx % 2) {
+		val &= ~MOXA_ODD_RS_MASK;
+		val |= FIELD_PREP(MOXA_ODD_RS_MASK, mode);
+	} else {
+		val &= ~MOXA_EVEN_RS_MASK;
+		val |= FIELD_PREP(MOXA_EVEN_RS_MASK, mode);
+	}
+	outb(val, UIR_addr);
+
+	return 0;
+}
+
 static int pci_moxa_init(struct pci_dev *dev)
 {
 	unsigned short device = dev->device;
 	resource_size_t iobar_addr = pci_resource_start(dev, 2);
-	unsigned int num_ports = (device & 0x00F0) >> 4;
+	unsigned int num_ports = (device & 0x00F0) >> 4, i;
 	u8 val;
 
+	if (!(pci_moxa_supported_rs(dev) & MOXA_SUPP_RS232)) {
+		for (i = 0; i < num_ports; ++i)
+			pci_moxa_set_interface(dev, i, MOXA_RS422);
+	}
+
 	/*
 	 * Enable hardware buffer to prevent break signal output when system boots up.
 	 * This hardware buffer is only supported on Mini PCIe series.
-- 
2.34.1