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

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Message-ID: <CAOMZO5ALSQj3C6Yn-avMZdzTvtWCZPQ5+pNdzYi03G-GZB_t+w@mail.gmail.com>
Date:   Sat, 7 Jan 2017 12:57:10 -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 Sat, Jan 7, 2017 at 11:45 AM, Clemens Gruber
<clemens.gruber@...ruber.com> wrote:

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

The MX6QDL_PAD_CSI0_DAT16__UART4_CTS_B option is only valid in dte mode.

If I pass 'fsl,dte-mode' then I can see this pin toggling. (rx, tx
would not work as expected).

In the default dce mode I can see UART4_CTS_B pin toggling when I
monitor CSI0_DAT17 pin and configure it as:

MX6QDL_PAD_CSI0_DAT17__UART4_CTS_B

,but unfortunately this pin does not go to the TXEN pin of the RS485
transceiver.

So this means that with the hardware I have access to my only
alternative is to set MX6QDL_PAD_CSI0_DAT16__GPIO6_IO02.

>> 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.

Yes, I have also tried when I read your email, but did not help on my case.

Thanks,

Fabio Estevam