linux-kernel - Re: [PATCH v3] serial: imx: warn user when using unsupported configuration

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Date:   Thu, 19 Apr 2018 18:26:14 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Stefan Agner <stefan@...er.ch>
Cc:     gregkh@...uxfoundation.org, lukas@...ner.de, jslaby@...e.com,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] serial: imx: warn user when using unsupported
 configuration

Hello Stefan,

On Thu, Apr 19, 2018 at 05:39:16PM +0200, Stefan Agner wrote:
> When using half-duplex mode (which disables receiver during txing)
> the RTS signal cannot be driven low during transmission when using
> i.MX UART RTS/CTS control. This seems to be a limitation of the
> i.MX UART IP: The RTS (CTS_B) signal is controlled by the receiver.
> When the receiver is disabled, the signal stays in UART logic idle
> state which is high...
> 
> If SER_RS485_RTS_ON_SEND is used, RTS needs to be high active during
> transmission. Since this is the default state of the RTS (CTS_B)
> signal when the receiver is off, half-duplex mode in this
> configuration works fine.
> 
> However, a low-active RTS signal (flag SER_RS485_RTS_ON_SEND not set)
> cannot be generated when the receiver is turned off.
> 
> Print an error if the user selects this unsupported configuration
> (both SER_RS485_RTS_ON_SEND and SER_RS485_RX_DURING_TX unset) and
> configure the closest working configuration (set the
> SER_RS485_RX_DURING_TX flag).
> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>
Acked-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>

Thanks
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |