Patch "tty: serial: 8250_omap: do not use RX DMA if pause is not supported" has been added to the 4.2-stable tree

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

tty: serial: 8250_omap: do not use RX DMA if pause is not supported

to the 4.2-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-8250_omap-do-not-use-rx-dma-if-pause-is-not-supported.patch

and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Sebastian Andrzej Siewior <[email protected]>
Date: Fri, 14 Aug 2015 17:52:07 +0200
Subject: tty: serial: 8250_omap: do not use RX DMA if pause is not supported

From: Sebastian Andrzej Siewior <[email protected]>

commit 830acf9e3044d4644f91b4418ef35a2094089946 upstream.

The 8250-omap driver requires the DMA-engine driver to support the pause command in order to properly turn off programmed RX transfer before the driver stars manually reading from the FIFO.
The lacking support of the requirement has been discovered recently. In order to stay safe here we disable RX-DMA completly on probe. The rx_dma_broken assignment on probe could be removed once we working pause function in omap-dma.

---
 drivers/tty/serial/8250/8250_omap.c |   14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

@@ -100,6 +100,7 @@ struct omap8250_priv {
 	struct work_struct qos_work;
 	struct uart_8250_dma omap8250_dma;
 	spinlock_t rx_dma_lock;
+	bool rx_dma_broken;
 };
 
 static u32 uart_read(struct uart_8250_port *up, u32 reg)

@@ -754,6 +755,7 @@ static void omap_8250_rx_dma_flush(struc
 	struct omap8250_priv	*priv = p->port.private_data;
 	struct uart_8250_dma	*dma = p->dma;
 	unsigned long		flags;
+	int ret;
 
 	spin_lock_irqsave(&priv->rx_dma_lock, flags);
 

@@ -762,7 +764,9 @@ static void omap_8250_rx_dma_flush(struc
 		return;
 	}
 
-	dmaengine_pause(dma->rxchan);
+	ret = dmaengine_pause(dma->rxchan);
+	if (WARN_ON_ONCE(ret))
+		priv->rx_dma_broken = true;
 
 	spin_unlock_irqrestore(&priv->rx_dma_lock, flags);
 

@@ -806,6 +810,9 @@ static int omap_8250_rx_dma(struct uart_
 		break;
 	}
 
+	if (priv->rx_dma_broken)
+		return -EINVAL;
+
 	spin_lock_irqsave(&priv->rx_dma_lock, flags);
 
 	if (dma->rx_running)

@@ -1180,6 +1187,11 @@ static int omap8250_probe(struct platfor
 
 			if (of_machine_is_compatible("ti,am33xx"))
 				priv->habit |= OMAP_DMA_TX_KICK;
+			/*
+			 * pause is currently not supported atleast on omap-sdma
+			 * and edma on most earlier kernels.
+			 */
+			priv->rx_dma_broken = true;
 		}
 	}
 #endif

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/tty-serial-8250_omap-do-not-use-rx-dma-if-pause-is-not-supported.patch