This is a note to let you know that I've just added the patch titled
dt-bindings: serial: Add common rs485 binding for RTS polarity
to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: dt-bindings-serial-add-common-rs485-binding-for-rts-polarity.patch and it can be found in the queue-4.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Fri Mar 16 15:11:07 CET 2018
From: Lukas Wunner lukas@wunner.de Date: Fri, 24 Nov 2017 23:26:40 +0100 Subject: dt-bindings: serial: Add common rs485 binding for RTS polarity
From: Lukas Wunner lukas@wunner.de
[ Upstream commit 6abe9ea8a5a5904d935b8a482117a7fd9b25f09e ]
rs485 allows for robust half-duplex serial communication. It is often implemented by attaching an rs485 transceiver to a UART. The UART's RTS line is wired to the transceiver's Transmit Enable pin and determines whether the transceiver is sending or receiving.
Examples for such transceivers are Maxim MAX13451E and TI SN65HVD1781A: https://datasheets.maximintegrated.com/en/ds/MAX13450E-MAX13451E.pdf http://www.ti.com/lit/ds/symlink/sn65hvd1781a-q1.pdf
In the devicetree, the transceiver itself is not represented, only the UART is. A few rs485-specific dt-bindings already exist and these go into the UART's device node.
This commit adds a binding to set the RTS polarity. Most (if not all) transceivers require the Transmit Enable pin be driven high for sending, but in some cases boards may negate the pin and RTS must then be driven low. Consequently the polarity defaults to active high but can be inverted with the newly added "rs485-rts-active-low" binding.
Document this binding in rs485.txt and in the two drivers fsl-imx-uart and fsl-lpuart that are about to be amended with support for it.
Curiously, the omap_serial driver defaults to active low and already supports an "rs485-rts-active-high" binding to invert the polarity. This is left unchanged to retain compatibility, but the binding is herewith documented.
Cc: Mark Jackson mpfj@newflow.co.uk Cc: Michał Oleszczyk oleszczyk.m@gmail.com Cc: Rafael Gago Castano rgc@hms.se Cc: Sascha Hauer s.hauer@pengutronix.de Acked-by: Rob Herring robh@kernel.org Signed-off-by: Lukas Wunner lukas@wunner.de Acked-by: Uwe Kleine-König u.kleine-koenig@pengutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Documentation/devicetree/bindings/serial/fsl-imx-uart.txt | 3 ++- Documentation/devicetree/bindings/serial/fsl-lpuart.txt | 3 ++- Documentation/devicetree/bindings/serial/omap_serial.txt | 1 + Documentation/devicetree/bindings/serial/rs485.txt | 1 + 4 files changed, 6 insertions(+), 2 deletions(-)
--- a/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt +++ b/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt @@ -9,7 +9,8 @@ Optional properties: - fsl,irda-mode : Indicate the uart supports irda mode - fsl,dte-mode : Indicate the uart works in DTE mode. The uart works in DCE mode by default. -- rs485-rts-delay, rs485-rx-during-tx, linux,rs485-enabled-at-boot-time: see rs485.txt +- rs485-rts-delay, rs485-rts-active-low, rs485-rx-during-tx, + linux,rs485-enabled-at-boot-time: see rs485.txt
Please check Documentation/devicetree/bindings/serial/serial.txt for the complete list of generic properties. --- a/Documentation/devicetree/bindings/serial/fsl-lpuart.txt +++ b/Documentation/devicetree/bindings/serial/fsl-lpuart.txt @@ -16,7 +16,8 @@ Required properties: Optional properties: - dmas: A list of two dma specifiers, one for each entry in dma-names. - dma-names: should contain "tx" and "rx". -- rs485-rts-delay, rs485-rx-during-tx, linux,rs485-enabled-at-boot-time: see rs485.txt +- rs485-rts-delay, rs485-rts-active-low, rs485-rx-during-tx, + linux,rs485-enabled-at-boot-time: see rs485.txt
Note: Optional properties for DMA support. Write them both or both not.
--- a/Documentation/devicetree/bindings/serial/omap_serial.txt +++ b/Documentation/devicetree/bindings/serial/omap_serial.txt @@ -20,6 +20,7 @@ Optional properties: node and a DMA channel number. - dma-names : "rx" for receive channel, "tx" for transmit channel. - rs485-rts-delay, rs485-rx-during-tx, linux,rs485-enabled-at-boot-time: see rs485.txt +- rs485-rts-active-high: drive RTS high when sending (default is low).
Example:
--- a/Documentation/devicetree/bindings/serial/rs485.txt +++ b/Documentation/devicetree/bindings/serial/rs485.txt @@ -12,6 +12,7 @@ Optional properties: * 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. If this property is not specified, <0 0> is assumed. +- rs485-rts-active-low: drive RTS low when sending (default is high). - 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. - rs485-rx-during-tx: empty property that enables the receiving of data even
Patches currently in stable-queue which might be from lukas@wunner.de are
queue-4.15/dt-bindings-serial-add-common-rs485-binding-for-rts-polarity.patch