1 files changed, 31 insertions, 0 deletions

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 90621c3312bc..194362d9f5a3 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -308,6 +308,7 @@ static unsigned int serial_in(struct uart_8250_port *up, int offset)
                 return inb(up->port.iobase + 1);
 
         case UPIO_MEM:
+        case UPIO_DWAPB:
                 return readb(up->port.membase + offset);
 
         case UPIO_MEM32:
@@ -333,6 +334,8 @@ static unsigned int serial_in(struct uart_8250_port *up, int offset)
 static void
 serial_out(struct uart_8250_port *up, int offset, int value)
 {
+        /* Save the offset before it's remapped */
+        int save_offset = offset;
         offset = map_8250_out_reg(up, offset) << up->port.regshift;
 
         switch (up->port.iotype) {
@@ -359,6 +362,18 @@ serial_out(struct uart_8250_port *up, int offset, int value)
                         writeb(value, up->port.membase + offset);
                 break;
 
+        case UPIO_DWAPB:
+                /* Save the LCR value so it can be re-written when a
+                 * Busy Detect interrupt occurs. */
+                if (save_offset == UART_LCR)
+                        up->lcr = value;
+                writeb(value, up->port.membase + offset);
+                /* Read the IER to ensure any interrupt is cleared before
+                 * returning from ISR. */
+                if (save_offset == UART_TX || save_offset == UART_IER)
+                        value = serial_in(up, UART_IER);
+                break;
+
         default:
                 outb(value, up->port.iobase + offset);
         }
@@ -373,6 +388,7 @@ serial_out_sync(struct uart_8250_port *up, int offset, int value)
 #ifdef CONFIG_SERIAL_8250_AU1X00
         case UPIO_AU:
 #endif
+        case UPIO_DWAPB:
                 serial_out(up, offset, value);
                 serial_in(up, UART_LCR);        /* safe, no side-effects */
                 break;
@@ -1389,6 +1405,19 @@ static irqreturn_t serial8250_interrupt(int irq, void *dev_id)
                         handled = 1;
 
                         end = NULL;
+                } else if (up->port.iotype == UPIO_DWAPB &&
+                          (iir & UART_IIR_BUSY) == UART_IIR_BUSY) {
+                        /* The DesignWare APB UART has an Busy Detect (0x07)
+                         * interrupt meaning an LCR write attempt occured while the
+                         * UART was busy. The interrupt must be cleared by reading
+                         * the UART status register (USR) and the LCR re-written. */
+                        unsigned int status;
+                        status = *(volatile u32 *)up->port.private_data;
+                        serial_out(up, UART_LCR, up->lcr);
+
+                        handled = 1;
+
+                        end = NULL;
                 } else if (end == NULL)
                         end = l;
 
@@ -2090,6 +2119,7 @@ static int serial8250_request_std_resource(struct uart_8250_port *up)
         case UPIO_TSI:
         case UPIO_MEM32:
         case UPIO_MEM:
+        case UPIO_DWAPB:
                 if (!up->port.mapbase)
                         break;
 
@@ -2127,6 +2157,7 @@ static void serial8250_release_std_resource(struct uart_8250_port *up)
         case UPIO_TSI:
         case UPIO_MEM32:
         case UPIO_MEM:
+        case UPIO_DWAPB:
                 if (!up->port.mapbase)
                         break;