serial: 8250_ingenic: Enable hardware flow control

The Ingenic UART is similar to a standard 16550, but hardware flow control
requires setting a couple of additional, non-standard bits in the MCR.

The non-standard "modem control enable" and "hardware flow control
mode" bits are set when writing to the MCR register, based
on whether the modem control interrupt is active.

Additionally the non-16550 compliant parts of the uart need to be
masked from higher layers.

Tested on Ingenic JZ4780 on MIPS Creator Ci20 board

Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_ingenic.c b/drivers/tty/serial/8250/8250_ingenic.c
index 7c1e4be..6cc05f8 100644 (file)
--- a/drivers/tty/serial/8250/8250_ingenic.c
+++ b/drivers/tty/serial/8250/8250_ingenic.c
@@ -34,6 +34,9 @@ struct ingenic_uart_data {
 
 #define UART_FCR_UME   BIT(4)
 
+#define UART_MCR_MDCE  BIT(7)
+#define UART_MCR_FCM   BIT(6)
+
 static struct earlycon_device *early_device;
 
 static uint8_t __init early_in(struct uart_port *port, int offset)
@@ -129,6 +132,8 @@ OF_EARLYCON_DECLARE(jz4780_uart, "ingenic,jz4780-uart",
 
 static void ingenic_uart_serial_out(struct uart_port *p, int offset, int value)
 {
+       int ier;
+
        switch (offset) {
        case UART_FCR:
                /* UART module enable */
@@ -136,9 +141,22 @@ static void ingenic_uart_serial_out(struct uart_port *p, int offset, int value)
                break;
 
        case UART_IER:
+               /* Enable receive timeout interrupt with the
+                * receive line status interrupt */
                value |= (value & 0x4) << 2;
                break;
 
+       case UART_MCR:
+               /* If we have enabled modem status IRQs we should enable modem
+                * mode. */
+               ier = p->serial_in(p, UART_IER);
+
+               if (ier & UART_IER_MSI)
+                       value |= UART_MCR_MDCE | UART_MCR_FCM;
+               else
+                       value &= ~(UART_MCR_MDCE | UART_MCR_FCM);
+               break;
+
        default:
                break;
        }
@@ -146,6 +164,28 @@ static void ingenic_uart_serial_out(struct uart_port *p, int offset, int value)
        writeb(value, p->membase + (offset << p->regshift));
 }
 
+static unsigned int ingenic_uart_serial_in(struct uart_port *p, int offset)
+{
+       unsigned int value;
+
+       value = readb(p->membase + (offset << p->regshift));
+
+       /* Hide non-16550 compliant bits from higher levels */
+       switch (offset) {
+       case UART_FCR:
+               value &= ~UART_FCR_UME;
+               break;
+
+       case UART_MCR:
+               value &= ~(UART_MCR_MDCE | UART_MCR_FCM);
+               break;
+
+       default:
+               break;
+       }
+       return value;
+}
+
 static int ingenic_uart_probe(struct platform_device *pdev)
 {
        struct uart_8250_port uart = {};
@@ -170,6 +210,7 @@ static int ingenic_uart_probe(struct platform_device *pdev)
        uart.port.mapbase = regs->start;
        uart.port.regshift = 2;
        uart.port.serial_out = ingenic_uart_serial_out;
+       uart.port.serial_in = ingenic_uart_serial_in;
        uart.port.irq = irq->start;
        uart.port.dev = &pdev->dev;