[PATCH 0/1] Synopsis 8250 serial port driver fix

[PATCH 0/1] Synopsis 8250 serial port driver fix

[Jonathan Richardson]

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

Desmond Liu (1):
  serial: 8250_dw: Fix get_mctrl behaviour

 .../bindings/serial/snps-dw-apb-uart.txt           |    7 ++++
 drivers/tty/serial/8250/8250_dw.c                  |   41 ++++++++++++++++++++
 2 files changed, 48 insertions(+)

-- 
1.7.9.5

--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[PATCH 1/1] serial: 8250_dw: Fix get_mctrl behaviour

[Jonathan Richardson]

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

Added device-tree property 'msr-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>
Reviewed-by: Jonathan Richardson <jonathar@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Tested-by: Scott Branden <sbranden@broadcom.com>
Tested-by: Jonathan Richardson <jonathar@broadcom.com>
Signed-off-by: Jonathan Richardson <jonathar@broadcom.com>
---
 .../bindings/serial/snps-dw-apb-uart.txt           |    7 ++++
 drivers/tty/serial/8250/8250_dw.c                  |   41 ++++++++++++++++++++
 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..010e52b 100644
--- a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
+++ b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
@@ -21,6 +21,12 @@ 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.
+- msr-override : array of strings to be used to override the individual
+  modem status signals for DCD, DSR, CTS, and RI.  If the property is not
+  present, the individual signals are obtained from the modem status register.
+  Strings accepted are "dcd", "dsr", "cts", and "ri". If "dcd", "dsr", or
+  "cts" are present, these signals will always be reported as active. If
+  "ri" is present, this signal will always be reported as inactive.
 
 Example:
 
@@ -31,6 +37,7 @@ Example:
 		interrupts = <10>;
 		reg-shift = <2>;
 		reg-io-width = <4>;
+		msr-override = "dcd", "dsr", cts", "ri"
 	};
 
 Example with one clock:
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 555de07..06dc873 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;
 }
 
@@ -290,6 +298,8 @@ static int dw8250_probe_of(struct uart_port *p,
 	u32			val;
 	bool has_ucv = true;
 	int id;
+	int msr_cnt, i;
+	const char *inp_name;
 
 #ifdef CONFIG_64BIT
 	if (of_device_is_compatible(np, "cavium,octeon-3860-uart")) {
@@ -334,6 +344,37 @@ static int dw8250_probe_of(struct uart_port *p,
 	if (id >= 0)
 		p->line = id;
 
+	msr_cnt = of_property_count_strings(np, "msr-override");
+
+	if (msr_cnt > 0) {
+		for (i = 0; i < msr_cnt; i++) {
+			of_property_read_string_index(np, "msr-override", i,
+				&inp_name);
+
+			if (!strcmp("dcd", inp_name)) {
+				/* Always report DCD as active */
+				data->msr_mask_on |= UART_MSR_DCD;
+				data->msr_mask_off |= UART_MSR_DDCD;
+			} else if (!strcmp("dsr", inp_name)) {
+				/* Always report DSR as active */
+				data->msr_mask_on |= UART_MSR_DSR;
+				data->msr_mask_off |= UART_MSR_DDSR;
+			} else if (!strcmp("cts", inp_name)) {
+				/* Always report CTS as active */
+				data->msr_mask_on |= UART_MSR_CTS;
+				data->msr_mask_off |= UART_MSR_DCTS;
+			} else if (!strcmp("ri", inp_name)) {
+				/* Always report Ring indicator as inactive */
+				data->msr_mask_off |= UART_MSR_RI;
+				data->msr_mask_off |= UART_MSR_TERI;
+			} else {
+				dev_err(p->dev,
+					"Ignore unknown msr-override %s\n",
+					inp_name);
+			}
+		}
+	}
+
 	/* clock got configured through clk api, all done */
 	if (p->uartclk)
 		return 0;
-- 
1.7.9.5

Re: [PATCH 1/1] serial: 8250_dw: Fix get_mctrl behaviour

[Arnd Bergmann]

On Wednesday 25 February 2015 11:04:16 Jonathan Richardson wrote:
> +- msr-override : array of strings to be used to override the individual
> +  modem status signals for DCD, DSR, CTS, and RI.  If the property is not
> +  present, the individual signals are obtained from the modem status register.
> +  Strings accepted are "dcd", "dsr", "cts", and "ri". If "dcd", "dsr", or
> +  "cts" are present, these signals will always be reported as active. If
> +  "ri" is present, this signal will always be reported as inactive.
> 

Did you copy this definition from another driver? If not, we should try
to come up with a more natural way to do it. How about defining four
boolean properties instead, like

	dcd-override
	dsr-override
	cts-override
	ri-override

Simplifies the parser and the binding.

	Arnd

Re: [PATCH 1/1] serial: 8250_dw: Fix get_mctrl behaviour

[Jonathan Richardson]

Hi Arnd,

On 15-02-25 11:21 AM, Arnd Bergmann wrote:
> On Wednesday 25 February 2015 11:04:16 Jonathan Richardson wrote:
>> +- msr-override : array of strings to be used to override the individual
>> +  modem status signals for DCD, DSR, CTS, and RI.  If the property is not
>> +  present, the individual signals are obtained from the modem status register.
>> +  Strings accepted are "dcd", "dsr", "cts", and "ri". If "dcd", "dsr", or
>> +  "cts" are present, these signals will always be reported as active. If
>> +  "ri" is present, this signal will always be reported as inactive.
>>
> 
> Did you copy this definition from another driver? If not, we should try
> to come up with a more natural way to do it. How about defining four
> boolean properties instead, like
> 
> 	dcd-override
> 	dsr-override
> 	cts-override
> 	ri-override
> 
> Simplifies the parser and the binding.

I didn't see anything similar in another driver. I agree with the bools
instead of strings. Did you want to keep these in the Synopsis driver
for now or were you thinking of putting them somewhere that they could
be re-used?

Thanks.

> 
> 	Arnd
> 

Re: [PATCH 1/1] serial: 8250_dw: Fix get_mctrl behaviour

[Arnd Bergmann]

On Wednesday 25 February 2015 12:00:15 Jonathan Richardson wrote:
> On 15-02-25 11:21 AM, Arnd Bergmann wrote:
> > On Wednesday 25 February 2015 11:04:16 Jonathan Richardson wrote:
> >> +- msr-override : array of strings to be used to override the individual
> >> +  modem status signals for DCD, DSR, CTS, and RI.  If the property is not
> >> +  present, the individual signals are obtained from the modem status register.
> >> +  Strings accepted are "dcd", "dsr", "cts", and "ri". If "dcd", "dsr", or
> >> +  "cts" are present, these signals will always be reported as active. If
> >> +  "ri" is present, this signal will always be reported as inactive.
> >>
> > 
> > Did you copy this definition from another driver? If not, we should try
> > to come up with a more natural way to do it. How about defining four
> > boolean properties instead, like
> > 
> >       dcd-override
> >       dsr-override
> >       cts-override
> >       ri-override
> > 
> > Simplifies the parser and the binding.
> 
> I didn't see anything similar in another driver. I agree with the bools
> instead of strings. Did you want to keep these in the Synopsis driver
> for now or were you thinking of putting them somewhere that they could
> be re-used?

I'm fine with it either way. Unless someone else has an opinion on the
matter, feel free to pick what makes sense to you.

	Arnd

[PATCH v2 0/1] Synopsis 8250 serial port driver fix

[Jonathan Richardson]

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

[PATCH v2 1/1] serial: 8250_dw: Fix get_mctrl behaviour

[Jonathan Richardson]

From: Desmond Liu <desmondl@broadcom.com>

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>
---
 .../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

Re: [PATCH v2 1/1] serial: 8250_dw: Fix get_mctrl behaviour

[Dmitry Torokhov]

On Thu, Feb 26, 2015 at 4:35 PM, Jonathan Richardson
<jonathar@broadcom.com> wrote:
> @@ -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;

This looks like a typo. Should the 1st line be data->msr_mask_on by any chance?

Thanks,
Dmitry

Re: [PATCH v2 1/1] serial: 8250_dw: Fix get_mctrl behaviour

[Jonathan Richardson]

On 15-03-09 11:40 AM, Dmitry Torokhov wrote:
> On Thu, Feb 26, 2015 at 4:35 PM, Jonathan Richardson
> <jonathar-dY08KVG/lbpWk0Htik3J/w@public.gmane.org> wrote:
>> @@ -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;
> 
> This looks like a typo. Should the 1st line be data->msr_mask_on by any chance?

I think the code is correct. The signals other than ri need to be
reported as active (masked on) if specified, but ri needs to be inactive
(masked off) unlike the other 3. This is stated in the kernel docs
mentioned in the commit. ri behaves differently than the others.

> 
> Thanks,
> Dmitry
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html