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Commit 442d5d17 authored by Razvan Stefanescu's avatar Razvan Stefanescu Committed by Greg Kroah-Hartman
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tty/serial: atmel: RS485 HD w/DMA: enable RX after TX is stopped 



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: b389f173 ("tty/serial: atmel: RS485 half duplex w/DMA: enable
RX after TX is done")
Signed-off-by: default avatarRazvan Stefanescu <razvan.stefanescu@microchip.com>
Acked-by: default avatarRichard Genoud <richard.genoud@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent b6b4bcb4

drivers/tty/serial/atmel_serial.c

+21 −3
Original line number Diff line number Diff line
@@ -163,6 +163,8 @@ struct atmel_uart_port { 
	unsigned int		pending_status;

	spinlock_t		lock_suspended;



	bool			hd_start_rx;	/* can start RX during half-duplex operation */



#ifdef CONFIG_PM

	struct {

		u32		cr;
@@ -805,8 +807,13 @@ 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);
@@ -1252,9 +1259,20 @@ 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);

	}

}