serial: 8250_dw: Fix get_mctrl behaviour

Fixed behaviour of get_mctrl() serial driver function as documented in:
https://www.kernel.org/doc/Documentation/serial/driver

Added device-tree properties 'dcd-override', 'dsr-override',
'cts-override', and 'ri-override' specific to the Synopsis 8250
DesignWare UART driver. Allows one to force Data Carrier Detect,
Clear To Send, and Data Set Ready signals to permanently be reported as
active. The Ring indicator can be forced to be reported as inactive.

It is possible that if modem control signalling is enabled on a port
that doesn't have these pins (e.g. - a simple two wire Tx/Rx port), the
driver can hang indefinitely waiting for the state to change. The new
DT properties allow the driver to ignore the state of these pins on
serial ports that don't support them, as recommended in the kernel
documentation.

Reviewed-by: JD (Jiandong) Zheng <jdzheng@broadcom.com>
Signed-off-by: Jonathan Richardson <jonathar@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
index 7f76214f728aa6028f133a94d04f183ccb3b1c38..289c40ed747042a70b13f9912dc0b5c443f7827e 100644 (file)
--- 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 e60116235836498e5b20ce56219b7d8c949acd25..2ab229ddee389ee20fa7923f93e43ddda944bbf0 100644 (file)
--- 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;