From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Fuzzey Subject: Serial ports with non connected RTS/CTS Date: Wed, 27 Jan 2016 11:30:32 +0100 Message-ID: <56A89C48.1040604@parkeon.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "linux-serial-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: devicetree@vger.kernel.org Hi all, currently, at least for 8250 based serial ports using of_serial, there is no way of indicating that the RTS / CTS lines, although supported by the UART, are not actually connected on the board. This means that userspace needs to know about this and not use the CRTSCTS termios flag (otherwise no data is sent). This is currently the case for Debian stattach for example (nettools 1.60) which unconditionally uses CRTSCTS (but the busybox version of slattach has a "-F" option that can be used to disable CRTSCTS). Would it not be better to allow this situation to be described in the device tree? Such an option already exists for the imx UART (""fsl,uart-has-rtscts") of_serial already has the "auto-flow-control" DT property but, as stated in the documentation: "The driver is allowed to detect support for the capability even without this property." In the past there was a (since reverted) property "has-hw-flow-control" See 06aa82e "serial: uart: add hw flow control support configuration" a6eec92 " Revert "serial: uart: add hw flow control support configuration" However that just provided another (redundant) way of *activating* hardware flow control and did not allow it to be disactivated. Would a new DT property "no-rtscts" to do this be acceptable? I think it would have to be a negative property to avoid breaking old device trees. Since there seems to have been some to and fro on this issue I thought it would be a good idea to discuss before writing the patch... Regards, Martin -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html