patch "tty/serial: atmel_serial: BUG: stop DMA from transmitting in stop_tx" added to tty-linus

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    tty/serial: atmel_serial: BUG: stop DMA from transmitting in stop_tx

to my tty git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-linus branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.

If you have any questions about this process, please let me know.


>From 89d8232411a85b9a6b12fd5da4d07d8a138a8e0c Mon Sep 17 00:00:00 2001
From: Richard Genoud <richard.genoud@gmail.com>
Date: Tue, 13 Dec 2016 17:27:56 +0100
Subject: tty/serial: atmel_serial: BUG: stop DMA from transmitting in stop_tx

If we don't disable the transmitter in atmel_stop_tx, the DMA buffer
continues to send data until it is emptied.
This cause problems with the flow control (CTS is asserted and data are
still sent).

So, disabling the transmitter in atmel_stop_tx is a sane thing to do.

Tested on at91sam9g35-cm(DMA)
Tested for regressions on sama5d2-xplained(Fifo) and at91sam9g20ek(PDC)

Cc: <stable@vger.kernel.org> (beware, this won't apply before 4.3)
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/serial/atmel_serial.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 168b10cad47b..f9d42de5ab2d 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -481,6 +481,14 @@ static void atmel_stop_tx(struct uart_port *port)
 		/* disable PDC transmit */
 		atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS);
 	}
+
+	/*
+	 * Disable the transmitter.
+	 * This is mandatory when DMA is used, otherwise the DMA buffer
+	 * is fully transmitted.
+	 */
+	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXDIS);
+
 	/* Disable interrupts */
 	atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask);
 
@@ -513,6 +521,9 @@ static void atmel_start_tx(struct uart_port *port)
 
 	/* Enable interrupts */
 	atmel_uart_writel(port, ATMEL_US_IER, atmel_port->tx_done_mask);
+
+	/* re-enable the transmitter */
+	atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN);
 }
 
 /*
-- 
2.11.0