[PATCH 3.14 40/44] serial: imx: Fix DMA handling for IDLE condition aborts

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Philipp Zabel <p.zabel@pengutronix.de>

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@gmx.net>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/tty/serial/imx.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -907,6 +907,14 @@ 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) {


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