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.pdfhttp://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>
Atmel USART, Freescale UARTs and OMAP UART all support the rs485 binding
described in rs485.txt, this commit just makes that explicit.
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
The lpuart of imx7ulp is basically the same as ls1021a. It's also
32 bit width register, but unlike ls1021a, it's little endian.
Besides that, imx7ulp lpuart has a minor different register layout
from ls1021a.
Cc: devicetree@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Stefan Agner <stefan@agner.ch>
Cc: Mingkai Hu <Mingkai.Hu@nxp.com>
Cc: Yangbo Lu <yangbo.lu@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
use exact SoC revision instead of wildcard describing
to make the binding more clearer.
Signed-off-by: Jingchang Lu <jingchang.lu@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This is a correction to the documentation. It was previously required but not documented.
Signed-off-by: Yuan Yao <yao.yuan@freescale.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Add dma support for lpuart. This function depend on DMA driver.
You can turn on it by write both the dmas and dma-name properties in dts node.
Signed-off-by: Yuan Yao <yao.yuan@freescale.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Move all bindings in bindings/tty/serial into bindings/serial so we only
have one place dir with serial/uart related bindings in it.
Signed-off-by: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Lukas Wunner