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>

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>
Desmond Liu · Greg Kroah-Hartman · Eric Lee · Eric Lee
1 parent 7cf91108d4
Showing 2 changed files with 48 additions and 0 deletions Side-by-side Diff
Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
drivers/tty/serial/8250/8250_dw.c
@@ -21,6 +21,18 @@
 - 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 @@
 		interrupts = <10>;
 		reg-shift = <2>;
 		reg-io-width = <4>;
+		dcd-override;
+		dsr-override;
+		cts-override;
+		ri-override;
 	};
  
 Example with one clock:
@@ -59,6 +59,8 @@
 	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 @@
 		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;
 }
  
@@ -333,6 +341,30 @@
 	id = of_alias_get_id(np, "serial");
 	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)
...	...	@@ -21,6 +21,18 @@
21	21	- reg-io-width : the size (in bytes) of the IO accesses that should be
22	22	performed on the device. If this property is not present then single byte
23	23	accesses are used.
	24	+- dcd-override : Override the DCD modem status signal. This signal will always
	25	+ be reported as active instead of being obtained from the modem status
	26	+ register. Define this if your serial port does not use this pin.
	27	+- dsr-override : Override the DTS modem status signal. This signal will always
	28	+ be reported as active instead of being obtained from the modem status
	29	+ register. Define this if your serial port does not use this pin.
	30	+- cts-override : Override the CTS modem status signal. This signal will always
	31	+ be reported as active instead of being obtained from the modem status
	32	+ register. Define this if your serial port does not use this pin.
	33	+- ri-override : Override the RI modem status signal. This signal will always be
	34	+ reported as inactive instead of being obtained from the modem status register.
	35	+ Define this if your serial port does not use this pin.
24	36
25	37	Example:
26	38
...	...	@@ -31,6 +43,10 @@
31	43	interrupts = <10>;
32	44	reg-shift = <2>;
33	45	reg-io-width = <4>;
	46	+ dcd-override;
	47	+ dsr-override;
	48	+ cts-override;
	49	+ ri-override;
34	50	};
35	51
36	52	Example with one clock:
...	...	@@ -59,6 +59,8 @@
59	59	u8 usr_reg;
60	60	int last_mcr;
61	61	int line;
	62	+ int msr_mask_on;
	63	+ int msr_mask_off;
62	64	struct clk *clk;
63	65	struct clk *pclk;
64	66	struct reset_control *rst;
...	...	@@ -81,6 +83,12 @@
81	83	value &= ~UART_MSR_DCTS;
82	84	}
83	85
	86	+ /* Override any modem control signals if needed */
	87	+ if (offset == UART_MSR) {
	88	+ value \|= d->msr_mask_on;
	89	+ value &= ~d->msr_mask_off;
	90	+ }
	91	+
84	92	return value;
85	93	}
86	94
...	...	@@ -333,6 +341,30 @@
333	341	id = of_alias_get_id(np, "serial");
334	342	if (id >= 0)
335	343	p->line = id;
	344	+
	345	+ if (of_property_read_bool(np, "dcd-override")) {
	346	+ /* Always report DCD as active */
	347	+ data->msr_mask_on \|= UART_MSR_DCD;
	348	+ data->msr_mask_off \|= UART_MSR_DDCD;
	349	+ }
	350	+
	351	+ if (of_property_read_bool(np, "dsr-override")) {
	352	+ /* Always report DSR as active */
	353	+ data->msr_mask_on \|= UART_MSR_DSR;
	354	+ data->msr_mask_off \|= UART_MSR_DDSR;
	355	+ }
	356	+
	357	+ if (of_property_read_bool(np, "cts-override")) {
	358	+ /* Always report DSR as active */
	359	+ data->msr_mask_on \|= UART_MSR_DSR;
	360	+ data->msr_mask_off \|= UART_MSR_DDSR;
	361	+ }
	362	+
	363	+ if (of_property_read_bool(np, "ri-override")) {
	364	+ /* Always report Ring indicator as inactive */
	365	+ data->msr_mask_off \|= UART_MSR_RI;
	366	+ data->msr_mask_off \|= UART_MSR_TERI;
	367	+ }
336	368
337	369	/* clock got configured through clk api, all done */
338	370	if (p->uartclk)