linux-kernel - [PATCH v2][RESEND] pch_uart: Fix dma channel unallocated issue

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Date:	Thu, 12 Apr 2012 10:47:50 +0900
From:	Tomoya MORINAGA <tomoya.rohm@...il.com>
To:	Alan Cox <alan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	qi.wang@...el.com, yong.y.wang@...el.com, joel.clark@...el.com,
	kok.howg.ewe@...el.com, Tomoya MORINAGA <tomoya.rohm@...il.com>
Subject: [PATCH v2][RESEND] pch_uart: Fix dma channel unallocated issue

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>
---
v2:  Re-create this patch for 3.4-rc2.
(RESEND) 1st v2 was sent to stable@...r.kernel.org. So, resend this patch
         with correct destination address.
---
 drivers/tty/serial/pch_uart.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
index 08b9962..80a32cf 100644
--- a/drivers/tty/serial/pch_uart.c
+++ b/drivers/tty/serial/pch_uart.c
@@ -1440,9 +1440,11 @@ 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;
-- 
1.7.7.6

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