2 files changed, 48 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
index 7f76214f728a..289c40ed7470 100644
--- a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
+++ b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
@@ -21,6 +21,18 @@ Optional properties:
 - reg-io-width : the size (in bytes) of the IO accesses that should be
   performed on the device.  If this property is not present then single byte
   accesses are used.
+- dcd-override : Override the DCD modem status signal. This signal will always
+  be reported as active instead of being obtained from the modem status
+  register. Define this if your serial port does not use this pin.
+- dsr-override : Override the DTS modem status signal. This signal will always
+  be reported as active instead of being obtained from the modem status
+  register. Define this if your serial port does not use this pin.
+- cts-override : Override the CTS modem status signal. This signal will always
+  be reported as active instead of being obtained from the modem status
+  register. Define this if your serial port does not use this pin.
+- ri-override : Override the RI modem status signal. This signal will always be
+  reported as inactive instead of being obtained from the modem status register.
+  Define this if your serial port does not use this pin.
 
 Example:
 
@@ -31,6 +43,10 @@ Example:
                 interrupts = <10>;
                 reg-shift = <2>;
                 reg-io-width = <4>;
+                dcd-override;
+                dsr-override;
+                cts-override;
+                ri-override;
         };
 
 Example with one clock:
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index e60116235836..2ab229ddee38 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -59,6 +59,8 @@ struct dw8250_data {
         u8                      usr_reg;
         int                     last_mcr;
         int                     line;
+        int                     msr_mask_on;
+        int                     msr_mask_off;
         struct clk              *clk;
         struct clk              *pclk;
         struct reset_control    *rst;
@@ -81,6 +83,12 @@ static inline int dw8250_modify_msr(struct uart_port *p, int offset, int value)
                 value &= ~UART_MSR_DCTS;
         }
 
+        /* Override any modem control signals if needed */
+        if (offset == UART_MSR) {
+                value |= d->msr_mask_on;
+                value &= ~d->msr_mask_off;
+        }
+
         return value;
 }
 
@@ -334,6 +342,30 @@ static int dw8250_probe_of(struct uart_port *p,
         if (id >= 0)
                 p->line = id;
 
+        if (of_property_read_bool(np, "dcd-override")) {
+                /* Always report DCD as active */
+                data->msr_mask_on |= UART_MSR_DCD;
+                data->msr_mask_off |= UART_MSR_DDCD;
+        }
+
+        if (of_property_read_bool(np, "dsr-override")) {
+                /* Always report DSR as active */
+                data->msr_mask_on |= UART_MSR_DSR;
+                data->msr_mask_off |= UART_MSR_DDSR;
+        }
+
+        if (of_property_read_bool(np, "cts-override")) {
+                /* Always report DSR as active */
+                data->msr_mask_on |= UART_MSR_DSR;
+                data->msr_mask_off |= UART_MSR_DDSR;
+        }
+
+        if (of_property_read_bool(np, "ri-override")) {
+                /* Always report Ring indicator as inactive */
+                data->msr_mask_off |= UART_MSR_RI;
+                data->msr_mask_off |= UART_MSR_TERI;
+        }
+
         /* clock got configured through clk api, all done */
         if (p->uartclk)
                 return 0;