linux-kernel - [ 028/167] [PATCH] pch_uart: Fix dma channel unallocated issue

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Message-Id: <20120509055033.426055874@decadent.org.uk>
Date:	Wed, 09 May 2012 06:50:57 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Tomoya MORINAGA <tomoya.rohm@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [ 028/167] [PATCH] pch_uart: Fix dma channel unallocated issue

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

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

From: Tomoya MORINAGA <tomoya.rohm@...il.com>

commit af6d17cdc8c89aeb3101f0d27cd32fc0592b40b2 upstream.

This driver anticipates pch_uart_verify_port() is not called
during installation.
However, actually pch_uart_verify_port() is called during
installation.
As a result, memory access violation occurs like below.

0. initial value: use_dma=0
1. starup()
    - dma channel is not allocated because use_dma=0
2. pch_uart_verify_port()
    - Set use_dma=1
3. UART processing acts DMA mode because use_dma=1
     - memory access violation occurs!

This patch fixes the issue.

Solution:
Whenever pch_uart_verify_port() is called and then
dma channel is not allocated, the channel should be allocated.

Signed-off-by: Tomoya MORINAGA <tomoya.rohm@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/tty/serial/pch_uart.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
index bbbec4a..c2816f4 100644
--- a/drivers/tty/serial/pch_uart.c
+++ b/drivers/tty/serial/pch_uart.c
@@ -1447,9 +1447,11 @@ static int pch_uart_verify_port(struct uart_port *port,
 			__func__);
 		return -EOPNOTSUPP;
 #endif
-		priv->use_dma = 1;
 		priv->use_dma_flag = 1;
 		dev_info(priv->port.dev, "PCH UART : Use DMA Mode\n");
+		if (!priv->use_dma)
+			pch_request_dma(port);
+		priv->use_dma = 1;
 	}
 
 	return 0;
-- 
1.7.10



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