From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: [PATCH v2 3/3] tty: Add software emulated RS485 support for 8250 Date: Tue, 10 Nov 2015 11:12:09 -0500 Message-ID: <56421759.8070103@hurleysoftware.com> References: <1446890976-1817-1-git-send-email-matwey@sai.msu.ru> <1446890976-1817-3-git-send-email-matwey@sai.msu.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1446890976-1817-3-git-send-email-matwey@sai.msu.ru> Sender: linux-kernel-owner@vger.kernel.org To: "Matwey V. Kornilov" Cc: gregkh@linuxfoundation.org, jslaby@suse.com, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, matwey.kornilov@gmail.com List-Id: linux-serial@vger.kernel.org Hi Matwey, I noticed 3 other issues here; see below. 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). > + if (p->port.rs485.delay_rts_before_send > 0) > + mdelay(p->port.rs485.delay_rts_before_send); > + } > + if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX)) > + serial8250_stop_rx(&p->port); > +} > +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; Unlike omap-serial, the 8250 stop_tx() will trigger _before_ the transmitter is drained. Some mechanism is required to defer until the transmitter is empty. > + 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); > + serial_port_out(&p->port, UART_MCR, UART_MCR_RTS); As with the SER_RS485_RTS_ON_SEND, RTS should be driven to either 0 or 1 here as well (not just to 1). Regards, Peter Hurley > + } > + /* > + * 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; >