[RFC PATCH] tty/serial: RS485 bindings for device tree

[RFC PATCH] tty/serial: RS485 bindings for device tree

[Nicolas Ferre]

Generic bindings for RS485 feature included in some UARTs.
Those bindings have to be used withing an UART device tree node.
Documentation updated to link to the bindings definition.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
---
Hi all,

1/ I have used the "linux" vendor definition: tell me if it makes sense...
2/ I have the feeling that the SER_RS485_RTS_ON_SEND flag can easily deduced
   from a zero value on both "before" and "after" data delays.

Tell me what you think about this...

Bye,

 Documentation/devicetree/bindings/serial/rs485.txt |   28 ++++++++++++++++++++
 Documentation/serial/serial-rs485.txt              |    5 +++
 2 files changed, 33 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/serial/rs485.txt

diff --git a/Documentation/devicetree/bindings/serial/rs485.txt b/Documentation/devicetree/bindings/serial/rs485.txt
new file mode 100644
index 0000000..6514be8
--- /dev/null
+++ b/Documentation/devicetree/bindings/serial/rs485.txt
@@ -0,0 +1,28 @@
+* RS485 serial communications
+
+The RTS signal is capable of automatically controlling line direction for
+the built-in half-duplex mode.
+The properties described hereafter shall be given to a half-duplex capable
+UART node.
+
+Optional properties:
+- linux,rs485-enabled-at-boot-time: empty property telling to enable the rs485
+  feature at boot time. It can be disabled later with proper ioctl.
+- linux,rs485-rts-delay: prop-encoded-array <a b> where:
+  * a is the delay beteween rts signal and beginning of data sent in milliseconds.
+      it corresponds to the delay before sending data.
+  * b is the delay between end of data sent and rts signal in milliseconds
+      it corresponds to the delay after sending data and actual release of the
+      line.
+
+RS485 example for Atmel USART:
+	usart0: serial@fff8c000 {
+		compatible = "atmel,at91sam9260-usart";
+		reg = <0xfff8c000 0x4000>;
+		interrupts = <7>;
+		atmel,use-dma-rx;
+		atmel,use-dma-tx;
+		linux,rs485-enabled-at-boot-time;
+		linux,rs485-rts-delay = <0 200>;	// in milliseconds
+	};
+
diff --git a/Documentation/serial/serial-rs485.txt b/Documentation/serial/serial-rs485.txt
index a493238..d11e5eb 100644
--- a/Documentation/serial/serial-rs485.txt
+++ b/Documentation/serial/serial-rs485.txt
@@ -28,6 +28,10 @@
    RS485 communications. This data structure is used to set and configure RS485
    parameters in the platform data and in ioctls.
 
+   The device tree can also provide RS485 boot time parameters (see [2]
+   for bindings). The driver is in charge of filling this data structure from
+   the values given by the device tree.
+
    Any driver for devices capable of working both as RS232 and RS485 should
    provide at least the following ioctls:
 
@@ -118,3 +122,4 @@
 5. REFERENCES
 
  [1]	include/linux/serial.h
+ [2]	Documentation/devicetree/bindings/serial/rs485.txt
-- 
1.7.5.4

Re: [RFC PATCH] tty/serial: RS485 bindings for device tree

[Nicolas Ferre]

I can also add this new property (support for it already in linux-next):

On 10/11/2011 07:13 PM, Nicolas Ferre :
> Generic bindings for RS485 feature included in some UARTs.
> Those bindings have to be used withing an UART device tree node.
> Documentation updated to link to the bindings definition.

[..]

> +Optional properties:
> +- linux,rs485-enabled-at-boot-time: empty property telling to enable the rs485
> +  feature at boot time. It can be disabled later with proper ioctl.

+- linux,rs485-rx-during-tx: empty property that enable the receiving of data
+  even whilst sending data.

> +- linux,rs485-rts-delay: prop-encoded-array <a b> where:

[..]

Best regards,
-- 
Nicolas Ferre

Re: [RFC PATCH] tty/serial: RS485 bindings for device tree

[Arnd Bergmann]

On Tuesday 11 October 2011 19:28:06 Nicolas Ferre wrote:
> 
> > +Optional properties:
> > +- linux,rs485-enabled-at-boot-time: empty property telling to enable the rs485
> > +  feature at boot time. It can be disabled later with proper ioctl.
> 
> +- linux,rs485-rx-during-tx: empty property that enable the receiving of data
> +  even whilst sending data.


This does not sound too linux specific. If it's a hardware property, don't
use the 'linux,' prefix and just make it 'rs484-full-duplex' or such.

	Arnd

Re: [RFC PATCH] tty/serial: RS485 bindings for device tree

[Nicolas Ferre]

On 10/11/2011 08:41 PM, Arnd Bergmann :
> On Tuesday 11 October 2011 19:28:06 Nicolas Ferre wrote:
>>
>>> +Optional properties:
>>> +- linux,rs485-enabled-at-boot-time: empty property telling to enable the rs485
>>> +  feature at boot time. It can be disabled later with proper ioctl.
>>
>> +- linux,rs485-rx-during-tx: empty property that enable the receiving of data
>> +  even whilst sending data.
> 
> This does not sound too linux specific. If it's a hardware property, don't
> use the 'linux,' prefix and just make it 'rs484-full-duplex' or such.

Ok, I understand. Your remark may also apply to linux,rs485-rts-delay.
So we may end-up with:

- linux,rs485-enabled-at-boot-time
- rs485-rx-during-tx
- rs485-rts-delay

Best regards,
-- 
Nicolas Ferre