From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751926AbbKIPpa (ORCPT ); Mon, 9 Nov 2015 10:45:30 -0500 Received: from mail-wm0-f46.google.com ([74.125.82.46]:35603 "EHLO mail-wm0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751682AbbKIPp0 (ORCPT ); Mon, 9 Nov 2015 10:45:26 -0500 MIME-Version: 1.0 In-Reply-To: <5640B071.8000806@hurleysoftware.com> References: <1446890976-1817-1-git-send-email-matwey@sai.msu.ru> <1446890976-1817-3-git-send-email-matwey@sai.msu.ru> <563E20DE.7000209@hurleysoftware.com> <5640B071.8000806@hurleysoftware.com> From: "Matwey V. Kornilov" Date: Mon, 9 Nov 2015 18:45:05 +0300 X-Google-Sender-Auth: qxUUEGREWo8rH975CJ4M2Na-t9Q Message-ID: Subject: Re: [PATCH v2 3/3] tty: Add software emulated RS485 support for 8250 To: Peter Hurley Cc: Greg KH , jslaby@suse.com, linux-serial@vger.kernel.org, linux-kernel Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2015-11-09 17:40 GMT+03:00 Peter Hurley : > On 11/08/2015 05:52 AM, Matwey V. Kornilov wrote: >> 2015-11-07 19:03 GMT+03:00 Peter Hurley : >>> Hi Matwey, >>> >>> 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. >>> >>> Comments below. >>> >>>> 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); >>>> } >>> >>> Newline req'd here. >>> >>>> +static void serial8250_stop_rx(struct uart_port *port); >>> >>> You can eliminate this forward decl by relocating serial8250_stop_rx() to here >>> (in a separate patch). >>> >>>> +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); >>>> + if (p->port.rs485.delay_rts_before_send > 0) >>>> + mdelay(p->port.rs485.delay_rts_before_send); >>> >>> So irqs are off for x msecs, and this cpu can't be used for anything else now? >>> I think this needs to be solved differently; maybe with a timer? >> >> Call of serial8250_start_tx is wrapped with spin_lock_irq in serial_core.c:2154 > > Yep, which is why I pointed out "irqs are off for x msecs". > >> I've tried to use msleep instead of mdelay but got "BUG: scheduling >> while atomic". > > Right, can't sleep while irqs are off, which is why I suggested something > like a timer. I am not sure that understand you correctly. Do you think that the following would be ok? wait_queue_head_t wait; init_waitqueue_head(&wait); wait_event_timeout(wait, 0, p->port.rs485.delay_rts_before_send * HZ / 1000); > > Regards, > Peter Hurley > >>>> + } >>>> + if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX)) >>>> + serial8250_stop_rx(&p->port); >>>> +} >>> >>> Newline req'd here. >>> >>>> +static void serial8250_rs485_stop_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_AFTER_SEND) { >>>> + if (p->port.rs485.delay_rts_after_send > 0) >>>> + mdelay(p->port.rs485.delay_rts_after_send); >>> >>> Same issue with irqs off. >>> >>>> + serial_port_out(&p->port, UART_MCR, UART_MCR_RTS); >>>> + } >>>> + /* >>>> + * Empty the RX FIFO, we are not interested in anything >>>> + * received during the half-duplex transmission. >>>> + */ >>>> + if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX)) >>>> + serial8250_clear_fifos(p); >>>> +} >>>> /* >>>> * IER sleep support. UARTs which have EFRs need the "extended >>>> * capability" bit enabled. Note that on XR16C850s, we need to >>>> @@ -1309,6 +1339,7 @@ static void serial8250_stop_tx(struct uart_port *port) >>>> up->acr |= UART_ACR_TXDIS; >>>> serial_icr_write(up, UART_ACR, up->acr); >>>> } >>>> + serial8250_rs485_stop_tx(up); >>>> serial8250_rpm_put(up); >>>> } >>>> >>>> @@ -1317,6 +1348,7 @@ static void serial8250_start_tx(struct uart_port *port) >>>> struct uart_8250_port *up = up_to_u8250p(port); >>>> >>>> serial8250_rpm_get_tx(up); >>>> + serial8250_rs485_start_tx(up); >>>> >>>> if (up->dma && !up->dma->tx_dma(up)) >>>> return; >>>> >>> >> >> >> > -- With best regards, Matwey V. Kornilov. Sternberg Astronomical Institute, Lomonosov Moscow State University, Russia 119991, Moscow, Universitetsky pr-k 13, +7 (495) 9392382