From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754176AbbKLNfY (ORCPT ); Thu, 12 Nov 2015 08:35:24 -0500 Received: from mail-ig0-f170.google.com ([209.85.213.170]:32879 "EHLO mail-ig0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753665AbbKLNfV (ORCPT ); Thu, 12 Nov 2015 08:35:21 -0500 Subject: Re: [PATCH v2 3/3] tty: Add software emulated RS485 support for 8250 To: "Matwey V. Kornilov" References: <1446890976-1817-1-git-send-email-matwey@sai.msu.ru> <1446890976-1817-3-git-send-email-matwey@sai.msu.ru> <56421759.8070103@hurleysoftware.com> Cc: Greg KH , jslaby@suse.com, linux-serial@vger.kernel.org, linux-kernel From: Peter Hurley Message-ID: <56449596.5020109@hurleysoftware.com> Date: Thu, 12 Nov 2015 08:35:18 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/12/2015 07:34 AM, Matwey V. Kornilov wrote: > 2015-11-10 19:12 GMT+03:00 Peter Hurley : >> On 11/07/2015 05:09 AM, Matwey V. Kornilov wrote: >>> Implementation of software emulation of RS485 direction handling is based >>> on omap-serial driver. It is acts as the following. At transmission start, >>> RTS is set (if required) and receiver is off (if required). At transmission >>> stop, RTS is set (if required) and fifo is flushed. >>> >>> Signed-off-by: Matwey V. Kornilov >>> --- >>> drivers/tty/serial/8250/8250_port.c | 32 ++++++++++++++++++++++++++++++++ >>> 1 file changed, 32 insertions(+) >>> >>> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c >>> index 52d82d2..a9291f7 100644 >>> --- a/drivers/tty/serial/8250/8250_port.c >>> +++ b/drivers/tty/serial/8250/8250_port.c >>> @@ -559,7 +559,37 @@ static void serial8250_rpm_put_tx(struct uart_8250_port *p) >>> pm_runtime_mark_last_busy(p->port.dev); >>> pm_runtime_put_autosuspend(p->port.dev); >>> } >>> +static void serial8250_stop_rx(struct uart_port *port); >>> +static void serial8250_rs485_start_tx(struct uart_8250_port *p) >>> +{ >>> + if (p->capabilities & UART_CAP_HW485 || !(p->port.rs485.flags & SER_RS485_ENABLED)) >>> + return; >>> + >>> + if (p->port.rs485.flags & SER_RS485_RTS_ON_SEND) { >>> + serial_port_out(&p->port, UART_MCR, UART_MCR_RTS); >> >> The SER_RS485_RTS_ON_SEND bit is supposed to be the logic level of RTS, >> so RTS should be driven to either 0 or 1 here (not just to 1). > > By the way, I've found that p->mcr caches MCR inconsistently. Is it > supposed to be so? Or p->mcr is not for caching? Not for caching; it's for modal settings (eg., AFE) that the 8250 port driver needs to merge in when changing mctrl bits (DTR/RTS/etc). The serial core caches the mctrl bits in uart_port->mctrl, but IMO it would be simpler to always set/clear RTS here (rather than like the omap-serial driver where it checks the gpio value first). Is the assumption that userspace will not perform conflicting operations, such as ioctl(TIOCMSET) or ioctl(TCSETSx), with RS485 enabled? Regards, Peter Hurley