linux-kernel - Re: imx: RS-485 problems during TX, maybe DMA related

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Date:   Sat, 7 Jan 2017 14:45:57 +0100
From:   Clemens Gruber <clemens.gruber@...ruber.com>
To:     Fabio Estevam <festevam@...il.com>
Cc:     linux-serial@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Nandor Han <nandor.han@...com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Fabio Estevam <fabio.estevam@...escale.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: imx: RS-485 problems during TX, maybe DMA related

Hi Fabio,

On Fri, Jan 06, 2017 at 10:31:16PM -0200, Fabio Estevam wrote:
> Yes, I have tried like this:
> 
> &uart4 {
>     pinctrl-names = "default";
>     pinctrl-0 = <&pinctrl_uart4>;
>     uart-has-rtscts;
>     status = "okay";
> };
> 
> pinctrl_uart4: uart4grp {
> fsl,pins = <
>     MX6QDL_PAD_CSI0_DAT12__UART4_TX_DATA 0x1b0b1
>     MX6QDL_PAD_KEY_ROW0__UART4_RX_DATA 0x1b0b1
>    MX6QDL_PAD_CSI0_DAT16__UART4_CTS_B 0x1b0b1
> >;
> };

I also mux RTS_B even though it is unused, not sure if it this makes a
difference to also add MX6QDL_PAD_CSI0_DAT17_UART4_RTS_B in your case?

It should work like this, I don't think using an extra GPIO is
necessary.

> 
> So I was never able to observe the DE pin toggling correctly.

But did you set SER_RS485_RX_DURING_TX in your flags? This is counter
intuitive, but I observed that it would not work otherwise.

> Maybe you could share your userspace application with me offline?

I am using a patched version of the busybox stty utility, I posted the
patch here, feel free to use it:
https://gist.github.com/clemensg/29bd68b3cfd719bd01002a2acde9662c

I use stty -F /dev/ttymxc4 clocal cread -hupcl -ixon -opost rs485
-rs485rtsonsend rs485rtsaftersend rs485rxduringtx

But for you it is probably rs485rtsonsend and -rs485rtsaftersend?

Regards,
Clemens