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Add RS485 mode support for UART2, UART3, UART4, and UART5. #6820

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Merged
pelwell merged 2 commits into from
Apr 28, 2025
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Add RS485 mode support for UART2, UART3, UART4, and UART5. #6820

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cf8b0d9
Add RS485 mode support for UART2, UART3, UART4, and UART5.
TheMightyMadman Apr 28, 2025
a0287d5
Modified potentially confusing documentation for rs485_invert_rts.
TheMightyMadman Apr 28, 2025
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48 changes: 48 additions & 0 deletions arch/arm/boot/dts/overlays/README
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Original file line number Diff line number Diff line change
Expand Up @@ -5181,6 +5181,18 @@ Name: uart2
Info: Enable uart 2 on GPIOs 0-3. BCM2711 only.
Load: dtoverlay=uart2,<param>
Params: ctsrts Enable CTS/RTS on GPIOs 2-3 (default off)
rs485 Enable RS485 mode for using the RTS line to
drive the OE pin of an RS485 transceiver (i.e.
MAX3078E); also enables the UARTx ctsrts
parameter, as RTS is required (default off).
rs485_invert_rts When RS485 mode is enabled, inverts the RTS
line from active-high (default) to active-low.
rs485_rts_on_delay When RS485 mode is enabled, sets the delay (in
milliseconds) between data transmission starting
and the RTS line being asserted (default 0).
rs485_rts_off_delay When RS485 mode is enabled, sets the delay (in
milliseconds) between data transmission ending
and the RTS line being deasserted (default 0).


Name: uart2-pi5
Expand All @@ -5193,6 +5205,18 @@ Name: uart3
Info: Enable uart 3 on GPIOs 4-7. BCM2711 only.
Load: dtoverlay=uart3,<param>
Params: ctsrts Enable CTS/RTS on GPIOs 6-7 (default off)
rs485 Enable RS485 mode for using the RTS line to
drive the OE pin of an RS485 transceiver (i.e.
MAX3078E); also enables the UARTx ctsrts
parameter, as RTS is required (default off).
rs485_invert_rts When RS485 mode is enabled, inverts the RTS
line from active-high (default) to active-low.
rs485_rts_on_delay When RS485 mode is enabled, sets the delay (in
milliseconds) between data transmission starting
and the RTS line being asserted (default 0).
rs485_rts_off_delay When RS485 mode is enabled, sets the delay (in
milliseconds) between data transmission ending
and the RTS line being deasserted (default 0).


Name: uart3-pi5
Expand All @@ -5205,6 +5229,18 @@ Name: uart4
Info: Enable uart 4 on GPIOs 8-11. BCM2711 only.
Load: dtoverlay=uart4,<param>
Params: ctsrts Enable CTS/RTS on GPIOs 10-11 (default off)
rs485 Enable RS485 mode for using the RTS line to
drive the OE pin of an RS485 transceiver (i.e.
MAX3078E); also enables the UARTx ctsrts
parameter, as RTS is required (default off).
rs485_invert_rts When RS485 mode is enabled, inverts the RTS
line from active-high (default) to active-low.
rs485_rts_on_delay When RS485 mode is enabled, sets the delay (in
milliseconds) between data transmission starting
and the RTS line being asserted (default 0).
rs485_rts_off_delay When RS485 mode is enabled, sets the delay (in
milliseconds) between data transmission ending
and the RTS line being deasserted (default 0).


Name: uart4-pi5
Expand All @@ -5217,6 +5253,18 @@ Name: uart5
Info: Enable uart 5 on GPIOs 12-15. BCM2711 only.
Load: dtoverlay=uart5,<param>
Params: ctsrts Enable CTS/RTS on GPIOs 14-15 (default off)
rs485 Enable RS485 mode for using the RTS line to
drive the OE pin of an RS485 transceiver (i.e.
MAX3078E); also enables the UARTx ctsrts
parameter, as RTS is required (default off).
rs485_invert_rts When RS485 mode is enabled, inverts the RTS
line from active-high (default) to active-low.
rs485_rts_on_delay When RS485 mode is enabled, sets the delay (in
milliseconds) between data transmission starting
and the RTS line being asserted (default 0).
rs485_rts_off_delay When RS485 mode is enabled, sets the delay (in
milliseconds) between data transmission ending
and the RTS line being deasserted (default 0).


Name: udrc
Expand Down
12 changes: 12 additions & 0 deletions arch/arm/boot/dts/overlays/uart2-overlay.dts
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,19 @@
};
};

rs485: fragment@2 {
target = <&uart2>;
__dormant__ {
linux,rs485-enabled-at-boot-time;
rs485-rts-delay = <0 0>;
};
};

__overrides__ {
ctsrts = <0>,"=1";
rs485 = <0>,"=1=2";
rs485_invert_rts = <&rs485>,"rs485-rts-active-low";
rs485_rts_on_delay = <&rs485>, "rs485-rts-delay:0";
rs485_rts_off_delay = <&rs485>, "rs485-rts-delay:4";
};
};
12 changes: 12 additions & 0 deletions arch/arm/boot/dts/overlays/uart3-overlay.dts
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,19 @@
};
};

rs485: fragment@2 {
target = <&uart3>;
__dormant__ {
linux,rs485-enabled-at-boot-time;
rs485-rts-delay = <0 0>;
};
};

__overrides__ {
ctsrts = <0>,"=1";
rs485 = <0>,"=1=2";
rs485_invert_rts = <&rs485>,"rs485-rts-active-low";
rs485_rts_on_delay = <&rs485>, "rs485-rts-delay:0";
rs485_rts_off_delay = <&rs485>, "rs485-rts-delay:4";
};
};
12 changes: 12 additions & 0 deletions arch/arm/boot/dts/overlays/uart4-overlay.dts
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,19 @@
};
};

rs485: fragment@2 {
target = <&uart4>;
__dormant__ {
linux,rs485-enabled-at-boot-time;
rs485-rts-delay = <0 0>;
};
};

__overrides__ {
ctsrts = <0>,"=1";
rs485 = <0>,"=1=2";
rs485_invert_rts = <&rs485>,"rs485-rts-active-low";
rs485_rts_on_delay = <&rs485>, "rs485-rts-delay:0";
rs485_rts_off_delay = <&rs485>, "rs485-rts-delay:4";
};
};
12 changes: 12 additions & 0 deletions arch/arm/boot/dts/overlays/uart5-overlay.dts
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,19 @@
};
};

rs485: fragment@2 {
target = <&uart5>;
__dormant__ {
linux,rs485-enabled-at-boot-time;
rs485-rts-delay = <0 0>;
};
};

__overrides__ {
ctsrts = <0>,"=1";
rs485 = <0>,"=1=2";
rs485_invert_rts = <&rs485>,"rs485-rts-active-low";
rs485_rts_on_delay = <&rs485>, "rs485-rts-delay:0";
rs485_rts_off_delay = <&rs485>, "rs485-rts-delay:4";
};
};
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