[3.16.y-ckt stable] Patch "serial: imx: Fix DMA handling for IDLE condition aborts" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    serial: imx: Fix DMA handling for IDLE condition aborts

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt14.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 1dc47ba3ed3b2c3c24585a325be1b9e36824d1d1 Mon Sep 17 00:00:00 2001
From: Philipp Zabel <p.zabel at pengutronix.de>
Date: Tue, 19 May 2015 10:54:09 +0200
Subject: serial: imx: Fix DMA handling for IDLE condition aborts

commit 392bceedb107a3dc1d4287e63d7670d08f702feb upstream.

The driver configures the IDLE condition to interrupt the SDMA engine.
Since the SDMA UART ROM script doesn't clear the IDLE bit itself, this
caused repeated 1-byte DMA transfers, regardless of available data in the
RX FIFO. Also, when returning due to the IDLE condition, the UART ROM
script already increased its counter, causing residue to be off by one.

This patch clears the IDLE condition to avoid repeated 1-byte DMA transfers
and decreases count by when the DMA transfer was aborted due to the IDLE
condition, fixing serial transfers using DMA on i.MX6Q.

Reported-by: Peter Seiderer <ps.report at gmx.net>
Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
Tested-by: Fabio Estevam <fabio.estevam at freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/tty/serial/imx.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 044e86d528ae..e30e52e378fe 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -913,6 +913,14 @@ static void dma_rx_callback(void *data)

 	status = dmaengine_tx_status(chan, (dma_cookie_t)0, &state);
 	count = RX_BUF_SIZE - state.residue;
+
+	if (readl(sport->port.membase + USR2) & USR2_IDLE) {
+		/* In condition [3] the SDMA counted up too early */
+		count--;
+
+		writel(USR2_IDLE, sport->port.membase + USR2);
+	}
+
 	dev_dbg(sport->port.dev, "We get %d bytes.\n", count);

 	if (count) {