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

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Date:   Fri, 6 Jan 2017 19:22:32 -0200
From:   Fabio Estevam <festevam@...il.com>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     "linux-serial@...r.kernel.org" <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-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: imx: RS-485 problems during TX, maybe DMA related

Hi Clemens,

On Wed, Jan 4, 2017 at 2:00 PM, Clemens Gruber
<clemens.gruber@...ruber.com> wrote:
> Hi,
>
> I observed odd behavior of the current tty/serial/imx.c driver in RS-485
> mode.
>
> RX works fine, but TX does not: When sending data, it arrives multiple

I am also trying to get rs485 in half-duplex mode to work on mx6dl
with kernel 4.9.

RX also works for me, but TX does not.

On my board it is the MX6QDL_PAD_CSI0_DAT16__UART4_RTS_B pin that
controls the rs485 transceiver flow, but I do not
see RTS to toggle to 1 during transmit. It stays always at 0.

I see you use CTS pin instead, but I thought RTS pin should be used.

On my userspace application I have:

/* enable RS485 mode: */
rs485conf.flags |= SER_RS485_ENABLED;

/* set logical level for RTS pin equal to 1 when sending: */
rs485conf.flags |= SER_RS485_RTS_ON_SEND;

/* set logical level for RTS pin equal to 0 after sending: */
rs485conf.flags &= ~(SER_RS485_RTS_AFTER_SEND);

Any ideas as to how to make RTS go to one so that the data can go
through the rs485 transceiver?

Thanks