Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752352AbbKIOk6 (ORCPT ); Mon, 9 Nov 2015 09:40:58 -0500 Received: from mail-qk0-f175.google.com ([209.85.220.175]:33591 "EHLO mail-qk0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751493AbbKIOkw (ORCPT ); Mon, 9 Nov 2015 09:40:52 -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> <563E20DE.7000209@hurleysoftware.com> Cc: Greg KH , jslaby@suse.com, linux-serial@vger.kernel.org, linux-kernel From: Peter Hurley Message-ID: <5640B071.8000806@hurleysoftware.com> Date: Mon, 9 Nov 2015 09:40:49 -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 Content-Length: 4199 Lines: 116 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. 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; >>> >> > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/