| Message ID | 01fc1e3d89037adce38177c3922d277584214fdd.1529911999.git.baruch@tkos.co.il (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi, On Mon, 25 Jun 2018 10:33:19 +0300 Baruch Siach wrote: > The i.MX UART peripheral uses the RST_B signal as input, and CTS_B as > output. This is just like the CDE role in RS-232. This is true > s/CDE/DCE/ > 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 RST as transceiver control signal. > s/RST/RTS/ > Add a note in the DT binding document about that, to reduce the > confusion somewhat. > > Signed-off-by: Baruch Siach <baruch@tkos.co.il> > --- > 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. Lothar Waßmann
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.
The i.MX UART peripheral uses the RST_B signal as input, and CTS_B as output. This is just like the CDE 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 RST 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> --- Documentation/devicetree/bindings/serial/fsl-imx-uart.txt | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)