The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 69646d7a3689fbe1a65ae90397d22ac3f1b8d40f Mon Sep 17 00:00:00 2001

From: Razvan Stefanescu razvan.stefanescu@microchip.com Date: Tue, 19 Mar 2019 15:20:35 +0200 Subject: [PATCH] tty/serial: atmel: RS485 HD w/DMA: enable RX after TX is stopped

In half-duplex operation, RX should be started after TX completes.

If DMA is used, there is a case when the DMA transfer completes but the TX FIFO is not emptied, so the RX cannot be restarted just yet.

Use a boolean variable to store this state and rearm TX interrupt mask to be signaled again that the transfer finished. In interrupt transmit handler this variable is used to start RX. A warning message is generated if RX is activated before TX fifo is cleared.

Fixes: b389f173aaa1 ("tty/serial: atmel: RS485 half duplex w/DMA: enable RX after TX is done") Signed-off-by: Razvan Stefanescu razvan.stefanescu@microchip.com Acked-by: Richard Genoud richard.genoud@gmail.com Cc: stable stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c index 55ca3416113f..0b4f36905321 100644 --- a/drivers/tty/serial/atmel_serial.c +++ b/drivers/tty/serial/atmel_serial.c @@ -166,6 +166,8 @@ struct atmel_uart_port { unsigned int pending_status; spinlock_t lock_suspended;

+ bool hd_start_rx; /* can start RX during half-duplex operation */ + /* ISO7816 */ unsigned int fidi_min; unsigned int fidi_max; @@ -933,8 +935,13 @@ static void atmel_complete_tx_dma(void *arg) if (!uart_circ_empty(xmit)) atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_tx); else if (atmel_uart_is_half_duplex(port)) { - /* DMA done, stop TX, start RX for RS485 */ - atmel_start_rx(port); + /* + * DMA done, re-enable TXEMPTY and signal that we can stop + * TX and start RX for RS485 + */ + atmel_port->hd_start_rx = true; + atmel_uart_writel(port, ATMEL_US_IER, + atmel_port->tx_done_mask); }

spin_unlock_irqrestore(&port->lock, flags); @@ -1382,9 +1389,20 @@ atmel_handle_transmit(struct uart_port *port, unsigned int pending) struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

if (pending & atmel_port->tx_done_mask) { - /* Either PDC or interrupt transmission */ atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask); + + /* Start RX if flag was set and FIFO is empty */ + if (atmel_port->hd_start_rx) { + if (!(atmel_uart_readl(port, ATMEL_US_CSR) + & ATMEL_US_TXEMPTY)) + dev_warn(port->dev, "Should start RX, but TX fifo is not empty\n"); + + atmel_port->hd_start_rx = false; + atmel_start_rx(port); + return; + } + atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_tx); } }