Hi,
This patchset fixes a bug in the Synopsis 8250 serial driver which causes the
driver to hang. The bug occurs on simple 2 wire serial ports when modem control
signalling has been enabled. It can be reproduced from user space by enabling
modem control signals (stty -clocal), then opening a serial port and polling for
data available to read with a timeout. A properly implemented driver will
ignore the control signals and the call to poll will return. The current
version of the driver hangs forever on the call to poll despite the timeout.
Jon
Changes from v1:
- Changed DT properties from strings to booleans as suggested by Arnd.
Documentation updated accordingly.
Desmond Liu (1):
serial: 8250_dw: Fix get_mctrl behaviour
.../bindings/serial/snps-dw-apb-uart.txt | 16 ++++++++++
drivers/tty/serial/8250/8250_dw.c | 32 ++++++++++++++++++++
2 files changed, 48 insertions(+)
--
1.7.9.5
From: Desmond Liu <[email protected]>
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 <[email protected]>
Signed-off-by: Jonathan Richardson <[email protected]>
---
.../bindings/serial/snps-dw-apb-uart.txt | 16 ++++++++++
drivers/tty/serial/8250/8250_dw.c | 32 ++++++++++++++++++++
2 files changed, 48 insertions(+)
diff --git a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
index 7f76214..289c40e 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 555de07..1f1d2e6 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;
--
1.7.9.5