From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: Serial ports with non connected RTS/CTS Date: Sat, 2 Apr 2016 21:36:38 -0700 Message-ID: <57009DD6.2050006@hurleysoftware.com> References: <56A89C48.1040604@parkeon.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <56A89C48.1040604-mB3Nsq4MPf1BDgjK7y7TUQ@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Martin Fuzzey Cc: "linux-serial-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: devicetree@vger.kernel.org On 01/27/2016 02:30 AM, Martin Fuzzey wrote: > 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... If I understand you correctly here 1) you want a way to describe the lack of CTS and RTS pins, and 2) you want the 8250 driver to mask off CRTSCTS when #1 is true. Sounds ok to me, but I'm not sure how userspace will respond to CRTSCTS not sticking. That will need some testing. Regards, Peter Hurley -- 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