Messages in this thread Patch in this message | | | From | "Matwey V. Kornilov" <> | Date | Tue, 10 Nov 2015 19:25:25 +0300 | Subject | Re: [PATCH v2 3/3] tty: Add software emulated RS485 support for 8250 |
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2015-11-10 19:12 GMT+03:00 Peter Hurley <peter@hurleysoftware.com>: > 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 <matwey@sai.msu.ru> >> --- >> 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. >
In serial8250_stop_tx() I see the following:
if (port->type == PORT_16C950) { up->acr |= UART_ACR_TXDIS; serial_icr_write(up, UART_ACR, up->acr); }
AFAIU this will disable transmission unconditionally, or not? What will happen here with data in FIFO?
I think that parts of my rs485 stuff have to be moved to serial8250_tx_chars where It will be simpler to handle things without involving mdelays.
>> + 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; >> >
-- With best regards, Matwey V. Kornilov. Sternberg Astronomical Institute, Lomonosov Moscow State University, Russia 119991, Moscow, Universitetsky pr-k 13, +7 (495) 9392382
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