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From: Baruch Siach <baruch@tkos.co.il>
To: Shawn Guo <shawnguo@kernel.org>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Fabio Estevam <fabio.estevam@nxp.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: devicetree@vger.kernel.org, "Baruch Siach" <baruch@tkos.co.il>,
	linux-serial@vger.kernel.org,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	linux-arm-kernel@lists.infradead.org,
	"Lothar Waßmann" <LW@KARO-electronics.de>
Subject: [PATCH v2] dt-bindings: serial: imx: clarify rs485 support usage
Date: Thu, 28 Jun 2018 10:25:32 +0300	[thread overview]
Message-ID: <e9beff38e9035c2f33d691f362e37d8e62aaa660.1530170732.git.baruch@tkos.co.il> (raw)

The i.MX UART peripheral uses the RST_B signal as input, and CTS_B as
output. This is just like the DCE role in RS-232. This is true
regardless of the "DTE mode" setting of this peripheral.

As a result, rs485 support hardware must use the CTS_B signal to control
the RS-485 transceiver. This is in contrast to generic rs485 kernel
code, documentation, and DT property names that consistently refer to
the RTS as transceiver control signal.

Add a note in the DT binding document about that, to reduce the
confusion somewhat.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
v2: Fix commit log typos (Lothar Waßmann)
---
 Documentation/devicetree/bindings/serial/fsl-imx-uart.txt | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt b/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt
index afcfbc34e243..35957cbf1571 100644
--- a/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt
+++ b/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt
@@ -9,7 +9,11 @@ Optional properties:
 - fsl,dte-mode : Indicate the uart works in DTE mode. The uart works
                   in DCE mode by default.
 - rs485-rts-delay, rs485-rts-active-low, rs485-rx-during-tx,
-  linux,rs485-enabled-at-boot-time: see rs485.txt
+  linux,rs485-enabled-at-boot-time: see rs485.txt. Note that for RS485
+  you must enable either the "uart-has-rtscts" or the "rts-gpios"
+  properties. In case you use "uart-has-rtscts" the signal that controls
+  the transceiver is actually CTS_B, not RTS_B. CTS_B is always output,
+  and RTS_B is input, regardless of dte-mode.
 
 Please check Documentation/devicetree/bindings/serial/serial.txt
 for the complete list of generic properties.
-- 
2.18.0


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WARNING: multiple messages have this Message-ID (diff)
From: baruch@tkos.co.il (Baruch Siach)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] dt-bindings: serial: imx: clarify rs485 support usage
Date: Thu, 28 Jun 2018 10:25:32 +0300	[thread overview]
Message-ID: <e9beff38e9035c2f33d691f362e37d8e62aaa660.1530170732.git.baruch@tkos.co.il> (raw)

The i.MX UART peripheral uses the RST_B signal as input, and CTS_B as
output. This is just like the DCE role in RS-232. This is true
regardless of the "DTE mode" setting of this peripheral.

As a result, rs485 support hardware must use the CTS_B signal to control
the RS-485 transceiver. This is in contrast to generic rs485 kernel
code, documentation, and DT property names that consistently refer to
the RTS as transceiver control signal.

Add a note in the DT binding document about that, to reduce the
confusion somewhat.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
v2: Fix commit log typos (Lothar Wa?mann)
---
 Documentation/devicetree/bindings/serial/fsl-imx-uart.txt | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt b/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt
index afcfbc34e243..35957cbf1571 100644
--- a/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt
+++ b/Documentation/devicetree/bindings/serial/fsl-imx-uart.txt
@@ -9,7 +9,11 @@ Optional properties:
 - fsl,dte-mode : Indicate the uart works in DTE mode. The uart works
                   in DCE mode by default.
 - rs485-rts-delay, rs485-rts-active-low, rs485-rx-during-tx,
-  linux,rs485-enabled-at-boot-time: see rs485.txt
+  linux,rs485-enabled-at-boot-time: see rs485.txt. Note that for RS485
+  you must enable either the "uart-has-rtscts" or the "rts-gpios"
+  properties. In case you use "uart-has-rtscts" the signal that controls
+  the transceiver is actually CTS_B, not RTS_B. CTS_B is always output,
+  and RTS_B is input, regardless of dte-mode.
 
 Please check Documentation/devicetree/bindings/serial/serial.txt
 for the complete list of generic properties.
-- 
2.18.0

             reply	other threads:[~2018-06-28  7:25 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-28  7:25 Baruch Siach [this message]
2018-06-28  7:25 ` [PATCH v2] dt-bindings: serial: imx: clarify rs485 support usage Baruch Siach
2018-06-28  8:14 ` Uwe Kleine-König
2018-06-28  8:14   ` Uwe Kleine-König
2018-06-28 16:30 ` Fabio Estevam
2018-06-28 16:30   ` Fabio Estevam
2018-07-03 23:10 ` Rob Herring
2018-07-03 23:10   ` Rob Herring

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