Patch "tty/serial: atmel_serial: BUG: stop DMA from transmitting in stop_tx" has been added to the 4.4-stable tree

[<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 the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tty-serial-atmel_serial-bug-stop-dma-from-transmitting-in-stop_tx.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>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

From: Richard Genoud <richard.genoud@gmail.com>

commit 89d8232411a85b9a6b12fd5da4d07d8a138a8e0c upstream.

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)

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(+)

--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -470,6 +470,14 @@ static void atmel_stop_tx(struct uart_po
 		/* 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);
 
@@ -502,6 +510,9 @@ static void atmel_start_tx(struct uart_p
 
 	/* 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);
 }
 
 /*


Patches currently in stable-queue which might be from richard.genoud@gmail.com are

queue-4.4/tty-serial-atmel_serial-bug-stop-dma-from-transmitting-in-stop_tx.patch