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patch "tty: serial: 8250_omap: do not use RX DMA if pause is not supported" added to tty-next

PATCH [email protected] 1 participant 1 message Aug 17, 2015

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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 my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-next 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 also be merged in the next major kernel release during the merge window.

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

Quoted 1 line

From 830acf9e3044d4644f91b4418ef35a2094089946 Mon Sep 17 00:00:00 2001

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

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.

Cc <[email protected]>
Signed-off-by Sebastian Andrzej Siewior <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 drivers/tty/serial/8250/8250_omap.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)
drivers/tty/serial/8250/8250_omap.c +13 -1
index 0340ee6ba970..826c5c4a2103 100644
@@ -112,6 +112,7 @@ 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)

@@ -761,6 +762,7 @@ static void omap_8250_rx_dma_flush(struct uart_8250_port *p)
 	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);
 

@@ -769,7 +771,9 @@ static void omap_8250_rx_dma_flush(struct uart_8250_port *p)
 		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);
 

@@ -813,6 +817,9 @@ static int omap_8250_rx_dma(struct uart_8250_port *p, unsigned int iir)
 		break;
 	}
 
+	if (priv->rx_dma_broken)
+		return -EINVAL;
+
 	spin_lock_irqsave(&priv->rx_dma_lock, flags);
 
 	if (dma->rx_running)

@@ -1207,6 +1214,11 @@ static int omap8250_probe(struct platform_device *pdev)
 
 			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
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2.5.0