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tty/serial: atmel: RS485 HD w/DMA: enable RX after TX is stopped

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commit 69646d7a3689fbe1a65ae90397d22ac3f1b8d40f 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>
This commit is contained in:
Razvan Stefanescu 2019-03-19 15:20:35 +02:00 • committed by Greg Kroah-Hartman
parent 59ae59920a
commit a6efba2fc3
1 changed files with 21 additions and 3 deletions
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24
drivers/tty/serial/atmel_serial.c
View file

@ -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);
@ -816,8 +818,13 @@ 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);
@ -1257,9 +1264,20 @@ 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);
}
}