[19/53] pch_uart: Fix DMA resource leak issue

Greg KH
2011-11-23T00:40:48Z

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

commit 90f04c2926cfb5bf74533b0a7766bc896f6a0c0e upstream.

Changing UART mode PIO->DMA->PIO->DMA like below, pch_uart driver can't get
DMA channel resource.

setserial /dev/ttyPCH0 ^low_latency
setserial /dev/ttyPCH0 low_latency

CAUSE:
Changing mode using setserial command, ".startup" function which gets DMA
channel is called before ".verify_port" function which sets
dma-flag(use_dma/use_dma_flag) as 1.

PIO->DMA
.startup: Since dma-flag is 0, DMA channel is not requested.
.verify_port: dma-flag is set as 1.
.shutdown: N/A

DMA->PIO
.startup: Since dma-flag is 1, DMA channel is requested.
.verify_port: dma-flag is set as 0.
.shutdown: Since dma-flag is 0, DMA channel is not released.

This means DMA channel resource leak occurs.
Next time, this driver can't get DMA channel resource forever.

MODIFICATION:
Currently, when release DMA channel resource, this driver checks dma-flag.
However, this specification occurs the above issue.
This driver must check whether dma_request_channel is executed or not.
The values are saved in private data variable "chan_tx/chan_tx".
These variables mean if the value is NULL, DMA channel is not requested,
if not NULL, DMA channel is requested.

This patch fixes the issue.

Signed-off-by: Tomoya MORINAGA <tomoya.rohm@gmail.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/tty/serial/pch_uart.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/tty/serial/pch_uart.c
+++ b/drivers/tty/serial/pch_uart.c
@@ -625,6 +625,7 @@ static void pch_request_dma(struct uart_
dev_err(priv->port.dev, "%s:dma_request_channel FAILS(Rx)\n",
__func__);
dma_release_channel(priv->chan_tx);
+ priv->chan_tx = NULL;
return;
}

@@ -1212,8 +1213,7 @@ static void pch_uart_shutdown(struct uar
dev_err(priv->port.dev,
"pch_uart_hal_set_fifo Failed(ret=%d)\n", ret);

- if (priv->use_dma_flag)
- pch_free_dma(port);
+ pch_free_dma(port);

free_irq(priv->port.irq, priv);
}