* [PATCH v2] Devicetree documentation: add rs485-rts-active-high property
@ 2017-11-07 7:53 Michal Oleszczyk
[not found] ` <20171107075336.11236-1-m.oleszczyk-z3quKL4iOrmQ6ZAhV5LmOA@public.gmane.org>
0 siblings, 1 reply; 2+ messages in thread
From: Michal Oleszczyk @ 2017-11-07 7:53 UTC (permalink / raw)
To: Rob Herring
Cc: Greg Kroah-Hartman, Mark Rutland,
linux-serial-u79uwXL29TY76Z2rM5mHXA,
devicetree-u79uwXL29TY76Z2rM5mHXA, Michal Oleszczyk
From: Michal Oleszczyk <oleszczyk.m-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Add description of rs485-rts-active-high property into
/serial/rs485.txt devicetree documentation file.
Signed-off-by: Michal Oleszczyk <oleszczyk.m-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
Repair 'From' to match with 'Signed-off-by' section.
Documentation/devicetree/bindings/serial/rs485.txt | 2 ++
1 file changed, 2 insertions(+)
diff --git a/Documentation/devicetree/bindings/serial/rs485.txt b/Documentation/devicetree/bindings/serial/rs485.txt
index b8415936dfdb..71c38ef7f6e2 100644
--- a/Documentation/devicetree/bindings/serial/rs485.txt
+++ b/Documentation/devicetree/bindings/serial/rs485.txt
@@ -16,6 +16,8 @@ Optional properties:
feature at boot time. It can be disabled later with proper ioctl.
- rs485-rx-during-tx: empty property that enables the receiving of data even
whilst sending data.
+- rs485-rts-active-high: empty property telling to set RTS line high when it is
+ active.
RS485 example for Atmel USART:
usart0: serial@fff8c000 {
--
2.11.0
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^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [v2] Devicetree documentation: add rs485-rts-active-high property
[not found] ` <20171107075336.11236-1-m.oleszczyk-z3quKL4iOrmQ6ZAhV5LmOA@public.gmane.org>
@ 2017-11-08 6:11 ` Lukas Wunner
0 siblings, 0 replies; 2+ messages in thread
From: Lukas Wunner @ 2017-11-08 6:11 UTC (permalink / raw)
To: Michal Oleszczyk
Cc: Rob Herring, Greg Kroah-Hartman, Mark Rutland,
linux-serial-u79uwXL29TY76Z2rM5mHXA,
devicetree-u79uwXL29TY76Z2rM5mHXA, Mark Jackson
On Tue, Nov 07, 2017 at 08:53:36AM +0100, Michal Oleszczyk wrote:
> From: Michal Oleszczyk <oleszczyk.m-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>
> Add description of rs485-rts-active-high property into
> /serial/rs485.txt devicetree documentation file.
Most rs485 transceivers on the market have an active-high Transmit Enable
pin, e.g. MAX13451E, SN65HVD1781A:
https://datasheets.maximintegrated.com/en/ds/MAX13450E-MAX13451E.pdf
http://www.ti.com/lit/gpn/sn65hvd1781a-q1
In fact I'm not aware of a single transceiver that uses active-low,
do you know one?
I know that omap-serial defaults to active-low and supports an
(as yet undocumented) "rs485-rts-active-high" property. I don't
know why it defaults to active-low. Adding Mark Jackson to cc
who introduced that feature with commit 4a0ac0f55.
All other drivers (e.g. imx.c, fsl-lpuart.c) default to active-high.
(Which in a way contradicts with your patch as it suggests *everything*
defaults to active-low.)
I have a series in preparation that I was going to post shortly
which instead introduces an rs485-rts-active-low property for
those presumably rare cases when it's needed, but retains the
current behaviour of omap-serial for compatibility:
https://github.com/l1k/linux/commit/03ef500e98e5
https://github.com/l1k/linux/commit/8430ffdb5799
https://github.com/l1k/linux/commit/c3a86d3b862b
In my opinion that's a better approach but I'd be curious to
hear other opinions.
Thanks,
Lukas
>
> Signed-off-by: Michal Oleszczyk <oleszczyk.m-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
> Repair 'From' to match with 'Signed-off-by' section.
>
> Documentation/devicetree/bindings/serial/rs485.txt | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/serial/rs485.txt b/Documentation/devicetree/bindings/serial/rs485.txt
> index b8415936dfdb..71c38ef7f6e2 100644
> --- a/Documentation/devicetree/bindings/serial/rs485.txt
> +++ b/Documentation/devicetree/bindings/serial/rs485.txt
> @@ -16,6 +16,8 @@ Optional properties:
> feature at boot time. It can be disabled later with proper ioctl.
> - rs485-rx-during-tx: empty property that enables the receiving of data even
> whilst sending data.
> +- rs485-rts-active-high: empty property telling to set RTS line high when it is
> + active.
>
> RS485 example for Atmel USART:
> usart0: serial@fff8c000 {
--
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2017-11-07 7:53 [PATCH v2] Devicetree documentation: add rs485-rts-active-high property Michal Oleszczyk
[not found] ` <20171107075336.11236-1-m.oleszczyk-z3quKL4iOrmQ6ZAhV5LmOA@public.gmane.org>
2017-11-08 6:11 ` [v2] " Lukas Wunner
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