Hi Magnus,
On Sat, Nov 20, 2021 at 5:32 PM Magnus Damm <damm@xxxxxxxxxxxxx> wrote:
> From: Magnus Damm <damm+renesas@xxxxxxxxxxxxx>
>
> Here's a work-in-progress patch for shared pin LED and KEY functionality:
> - UART TX Serdev LED driver prototype (functional)
> - UART RX Serdev KEY driver prototype (partial)
> - r8a77995 Draak DTS modifications to use above drivers with SCIF0
>
> With this code my hope is to use hardware to drive an LED and allow
> detection of a key press without software performing any kind of polling.
>
> In theory on SoCs that support UART RX and TX on the same pin (and also
> open drain output) with the above software it is possible to handle boards
> with single pin shared LED and KEY functionality.
>
> This prototype on r8a77995 Draak makes use of 3 pins and an external circuit:
> - LED13/SW59/GP4_07 <-> EXIO_A:10 (CN46)
> - SCIF0_RX/GP4_20 <- EXIO_A:38 (CN46)
> - SCIF0_TX/GP4_21 -> EXIO_A:36 (CN46)
> Ether-AVB PHY connector (CN23) has 3.3V on pin 54 and 56 and GND on 14
> In the future SCIF1 and SCIF3 may also be used for other LEDs and switches.
>
> Currently two inverters on SN74HC05 together with pull-ups are used to extend
> the D3 SoC and the Draak board with open drain functionality and also tie
> together the TX and RX pins with LED13/SW59.
>
> The prototype LED driver allows user space to turn on/off the LED using:
> # echo 1 > /sys/class/leds/serial0-0/brightness
> # echo 0 > /sys/class/leds/serial0-0/brightness
> Must be easy to extend the driver with some degree of brightness control.
>
> Apart from some general brush up the following issues have surfaced:
> - "controller busy" error happens when more than one serdev is used
> - it is unclear how to take RX errors from serdev and generate key events
> - there seem to be no way to silence "sh-sci e6e60000.serial: frame error"
> - the DTS "current-speed" property looks like sw config and not hw description
>
> Obviously not for upstream merge as-is. Might however be useful as SCIF error
> test bench and/or as potential (corner) use case for serdev.
>
> Not-Yet-Signed-off-by: Magnus Damm <damm+renesas@xxxxxxxxxxxxx>
Thanks for your patch, which is definitely an interesting approach!
> --- 0001/arch/arm64/boot/dts/renesas/r8a77995-draak.dts
> +++ work/arch/arm64/boot/dts/renesas/r8a77995-draak.dts 2021-11-20 23:47:14.965609878 +0900
> @@ -479,13 +495,29 @@
> status = "okay";
> };
>
> +&scif0 {
> + pinctrl-0 = <&scif0_pins>;
> + pinctrl-names = "default";
> +
> + status = "okay";
> +#if 1
> + led {
> + compatible = "serdev,led";
> + current-speed = <9600>;
> + };
> +#else
> + key {
> + compatible = "serdev,key";
> + current-speed = <9600>;
> + };
> +#endif
So LED and key are still mutually-exclusive, despite using 3 signals
into the SoC?
> +};
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
