On 11/8/19 3:41 PM, Falco Hyfing wrote: Hi, > I stumbled upon this unresolved issue where the TI AM335x UART is > sporadically swallowing the first byte using the 8250_omap driver in > RS485 mode. > > Previous discussions of the issue ended on Christmas Eve last year. For > reference: > https://marc.info/?w=2&r=1&s=fix+clearing+fifos+rs485+mode+again&q=t Right, I'm sorry for not following up on that thread anymore. I was ill during that time and I didn't have the energy to counter all those negative emails. So thanks for picking this up. I think the issue is a generic one though, and affects various other 16550 UARTs, it's not isolated to the OMAP UART, which is why I patched the generic code. I think if we could solve the quirk of that JZ4780 UART, the generic approach would work. > As our company plans to move our serial device servers' firmware to an > upstream kernel version we need a solution for this problem. > > I appended a small patch that seems to resolve the issue for our products. > > I would like to kindly ask whether you could test this patch with > various serial hardware that would be affected by this driver. > > Kind regards, > > Falco Hyfing > Software Engineer at VisionSystems GmbH > > > diff --git a/drivers/tty/serial/8250/8250_port.c > b/drivers/tty/serial/8250/8250_port.c > index 8407166610ce..25dd44d5f6ff 100644 > --- a/drivers/tty/serial/8250/8250_port.c > +++ b/drivers/tty/serial/8250/8250_port.c > @@ -1405,7 +1405,8 @@ static void __do_stop_tx_rs485(struct > uart_8250_port *p) > * Enable previously disabled RX interrupts. > */ > if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX)) { > - serial8250_clear_and_reinit_fifos(p); > + serial_port_out(&p->port, UART_FCR, p->fcr | > + UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT); > > p->ier |= UART_IER_RLSI | UART_IER_RDI; > serial_port_out(&p->port, UART_IER, p->ier); > -- Best regards, Marek Vasut
