commit 69646d7a3689 ("tty/serial: atmel: RS485 HD w/DMA: enable RX after TX is stopped") upstream.

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 --- drivers/tty/serial/atmel_serial.c | 24 +++++++++++++++++++++--- 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c index a1303df0abb7..132e5a5ec069 100644 --- a/drivers/tty/serial/atmel_serial.c +++ b/drivers/tty/serial/atmel_serial.c @@ -169,6 +169,8 @@ struct atmel_uart_port { unsigned int pending_status; spinlock_t lock_suspended;

+ bool hd_start_rx; /* can start RX during half-duplex operation */ + int (*prepare_rx)(struct uart_port *port); int (*prepare_tx)(struct uart_port *port); void (*schedule_rx)(struct uart_port *port); @@ -815,8 +817,13 @@ static void atmel_complete_tx_dma(void *arg) if (!uart_circ_empty(xmit)) tasklet_schedule(&atmel_port->tasklet); 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); @@ -1256,9 +1263,20 @@ 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; + } + tasklet_schedule(&atmel_port->tasklet); } }