From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Agner Subject: Re: [PATCH v2] serial: imx: warn user when using unsupported configuration Date: Wed, 18 Apr 2018 17:30:42 +0200 Message-ID: <6cdfd27073006d0959c21eca23fa56e1@agner.ch> References: <20180418140638.19331-1-stefan@agner.ch> <20180418145341.xwsah7spyfazcb63@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20180418145341.xwsah7spyfazcb63@pengutronix.de> Sender: linux-kernel-owner@vger.kernel.org To: =?UTF-8?Q?Uwe_Kleine-K=C3=B6nig?= Cc: gregkh@linuxfoundation.org, lukas@wunner.de, jslaby@suse.com, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-serial@vger.kernel.org On 18.04.2018 16:53, Uwe Kleine-König wrote: > On Wed, Apr 18, 2018 at 04:06:38PM +0200, Stefan Agner wrote: >> When using half-duplex mode (which disables receiver during txing) >> the RTS signal cannot be driven low during transmission. 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 >> --- >> Changes since v1: >> - Consistently check for sport->have_rtscts && !(rs485conf->flags & >> SER_RS485_RTS_ON_SEND) >> - Don't break printed message >> >> drivers/tty/serial/imx.c | 15 +++++++++++++++ >> 1 file changed, 15 insertions(+) >> >> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c >> index 91f3a1a5cb7f..1c1080fc8084 100644 >> --- a/drivers/tty/serial/imx.c >> +++ b/drivers/tty/serial/imx.c >> @@ -1833,6 +1833,11 @@ static int imx_uart_rs485_config(struct uart_port *port, >> rs485conf->flags &= ~SER_RS485_ENABLED; >> >> if (rs485conf->flags & SER_RS485_ENABLED) { >> + /* Enable receiver if low-active RTS signal is requested */ >> + if (sport->have_rtscts && >> + !(rs485conf->flags & SER_RS485_RTS_ON_SEND)) >> + rs485conf->flags |= SER_RS485_RX_DURING_TX; >> + > > I wonder what should happen, if the device tree has both > > uart-has-rtscts; > rts-gpios = <...>; Hm, it seems that the code controls both in that case. > > . I think the right thing would be to check for > > sport->have_rtscts && !sport->have_rtsgpio I agree, since it controls both one can use the GPIO to have a working half duplex with low-active RTS configuration. Will send v3. -- Stefan