Re: [PATCH v3 00/12] Add RS485 support to DW UART

[Vicente Bergas <vicencb@gmail.com>]

Hi Lukas,

On Thu, Apr 21, 2022 at 9:38 PM Lukas Wunner <lukas@wunner.de> wrote:
>
> On Thu, Apr 21, 2022 at 05:36:26PM +0200, Vicente Bergas wrote:
> > 2.- Although "linux,rs485-enabled-at-boot-time" is set in the DTS,
> > the RTS/DriverEnable line is asserted all the time the /dev/ttyS1
> > device file is closed.
> > As soon as the device file is openned, the RTS line is deasserted.
> > Then it works as expected: it is asserted only during transmissions.
> > When the device file is closed again, the RTS line goes back to the
> > asserted level and stays there.
> > When the rs485 mode is enabled, it is expected that the RTS line be
> > deasserted by default.
>
> That's probably the same issue as reported here:
>
> https://lore.kernel.org/linux-serial/20220329085050.311408-1-matthias.schiffer@ew.tq-group.com/
>
> Basically, some drivers have historically used inverse RTS polarity
> and others haven't.  I'm still busy sorting out which drivers use
> which.  Sorry, this is quite complex and takes some time.
>
> Have you configured "rs485-rts-active-low" in the device tree?

The UART configuration is the default from rk3328.dtsi plus:
&uart1 {
  linux,rs485-enabled-at-boot-time;
  pinctrl-0 = <&uart1_xfer &uart1_cts &uart1_rts_pin>;
  rs485-rts-delay = <0 52>;
  rs485-rx-during-tx;
  rts-gpios = <&gpio3 RK_PA5 GPIO_ACTIVE_HIGH>;
  status = "okay";
};

So, it is asserted high and deasserted low.

> Which kernel version are you using exactly?

5.17.3 and 5.17.4
Also, i am about to test 5.18-rc3

> Thanks,
>
> Lukas

Regards,
  Vicente.