2021-04-11 09:40:55

by Dario Binacchi

Subject: [PATCH v2] serial: omap: fix rs485 half-duplex filtering

Data received during half-duplex transmission must be filtered.
If the target device responds quickly, emptying the FIFO at the end of
the transmission can erase not only the echo characters but also part of
the response message.
By keeping the receive interrupt enabled even during transmission, it
allows you to filter each echo character and only in a number equal to
those transmitted.
The issue was generated by a target device that started responding
240us later having received a request in communication at 115200bps.
Sometimes, some messages received by the target were missing some of the
first bytes.

Signed-off-by: Dario Binacchi <[email protected]>


---

Changes in v2:
- Fix compiling error

drivers/tty/serial/omap-serial.c | 39 ++++++++++++++++++++------------
1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 76b94d0ff586..c0df22b7ea5e 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -159,6 +159,8 @@ struct uart_omap_port {
u32 calc_latency;
struct work_struct qos_work;
bool is_suspending;
+
+ atomic_t rs485_tx_filter_count;
};

#define to_uart_omap_port(p) ((container_of((p), struct uart_omap_port, port)))
@@ -328,19 +330,6 @@ static void serial_omap_stop_tx(struct uart_port *port)
serial_out(up, UART_IER, up->ier);
}

- if ((port->rs485.flags & SER_RS485_ENABLED) &&
- !(port->rs485.flags & SER_RS485_RX_DURING_TX)) {
- /*
- * Empty the RX FIFO, we are not interested in anything
- * received during the half-duplex transmission.
- */
- serial_out(up, UART_FCR, up->fcr | UART_FCR_CLEAR_RCVR);
- /* Re-enable RX interrupts */
- up->ier |= UART_IER_RLSI | UART_IER_RDI;
- up->port.read_status_mask |= UART_LSR_DR;
- serial_out(up, UART_IER, up->ier);
- }
-
pm_runtime_mark_last_busy(up->dev);
pm_runtime_put_autosuspend(up->dev);
}
@@ -366,6 +355,10 @@ static void transmit_chars(struct uart_omap_port *up, unsigned int lsr)
serial_out(up, UART_TX, up->port.x_char);
up->port.icount.tx++;
up->port.x_char = 0;
+ if ((up->port.rs485.flags & SER_RS485_ENABLED) &&
+ !(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
+ atomic_inc(&up->rs485_tx_filter_count);
+
return;
}
if (uart_circ_empty(xmit) || uart_tx_stopped(&up->port)) {
@@ -377,6 +370,10 @@ static void transmit_chars(struct uart_omap_port *up, unsigned int lsr)
serial_out(up, UART_TX, xmit->buf[xmit->tail]);
xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
up->port.icount.tx++;
+ if ((up->port.rs485.flags & SER_RS485_ENABLED) &&
+ !(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
+ atomic_inc(&up->rs485_tx_filter_count);
+
if (uart_circ_empty(xmit))
break;
} while (--count > 0);
@@ -420,7 +417,7 @@ static void serial_omap_start_tx(struct uart_port *port)

if ((port->rs485.flags & SER_RS485_ENABLED) &&
!(port->rs485.flags & SER_RS485_RX_DURING_TX))
- serial_omap_stop_rx(port);
+ atomic_set(&up->rs485_tx_filter_count, 0);

serial_omap_enable_ier_thri(up);
pm_runtime_mark_last_busy(up->dev);
@@ -491,8 +488,13 @@ static void serial_omap_rlsi(struct uart_omap_port *up, unsigned int lsr)
* Read one data character out to avoid stalling the receiver according
* to the table 23-246 of the omap4 TRM.
*/
- if (likely(lsr & UART_LSR_DR))
+ if (likely(lsr & UART_LSR_DR)) {
serial_in(up, UART_RX);
+ if ((up->port.rs485.flags & SER_RS485_ENABLED) &&
+ !(up->port.rs485.flags & SER_RS485_RX_DURING_TX) &&
+ atomic_read(&up->rs485_tx_filter_count))
+ atomic_dec(&up->rs485_tx_filter_count);
+ }

up->port.icount.rx++;
flag = TTY_NORMAL;
@@ -543,6 +545,13 @@ static void serial_omap_rdi(struct uart_omap_port *up, unsigned int lsr)
return;

ch = serial_in(up, UART_RX);
+ if ((up->port.rs485.flags & SER_RS485_ENABLED) &&
+ !(up->port.rs485.flags & SER_RS485_RX_DURING_TX) &&
+ atomic_read(&up->rs485_tx_filter_count)) {
+ atomic_dec(&up->rs485_tx_filter_count);
+ return;
+ }
+
flag = TTY_NORMAL;
up->port.icount.rx++;

--
2.17.1

2021-04-15 08:16:20

by Greg Kroah-Hartman

Subject: Re: [PATCH v2] serial: omap: fix rs485 half-duplex filtering

On Sun, Apr 11, 2021 at 11:38:55AM +0200, Dario Binacchi wrote:
> Data received during half-duplex transmission must be filtered.
> If the target device responds quickly, emptying the FIFO at the end of
> the transmission can erase not only the echo characters but also part of
> the response message.
> By keeping the receive interrupt enabled even during transmission, it
> allows you to filter each echo character and only in a number equal to
> those transmitted.
> The issue was generated by a target device that started responding
> 240us later having received a request in communication at 115200bps.
> Sometimes, some messages received by the target were missing some of the
> first bytes.
>
> Signed-off-by: Dario Binacchi <[email protected]>
>

What commit id does this patch "fix"? Please resend that and add a
"Fixes:" tag right above your signed-off-by line.

thanks,

greg k-h