serial: samsung: Add missing checks for dma_map_single failure

This patch adds missing checks for dma_map_single() failure and proper error
reporting. Although this issue was harmless on ARM architecture, it is always
good to use the DMA mapping API in a proper way. This patch fixes the following
DMA API debug warning:

WARNING: CPU: 1 PID: 3785 at lib/dma-debug.c:1171 check_unmap+0x8a0/0xf28
dma-pl330 121a0000.pdma: DMA-API: device driver failed to check map error[device address=0x000000006e0f9000] [size=4096 bytes] [mapped as single]
Modules linked in:
CPU: 1 PID: 3785 Comm: (agetty) Tainted: G        W       4.11.0-rc1-00137-g07ca963-dirty #59
Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[<c011aaa4>] (unwind_backtrace) from [<c01127c0>] (show_stack+0x20/0x24)
[<c01127c0>] (show_stack) from [<c06ba5d8>] (dump_stack+0x84/0xa0)
[<c06ba5d8>] (dump_stack) from [<c0139528>] (__warn+0x14c/0x180)
[<c0139528>] (__warn) from [<c01395a4>] (warn_slowpath_fmt+0x48/0x50)
[<c01395a4>] (warn_slowpath_fmt) from [<c072a114>] (check_unmap+0x8a0/0xf28)
[<c072a114>] (check_unmap) from [<c072a834>] (debug_dma_unmap_page+0x98/0xc8)
[<c072a834>] (debug_dma_unmap_page) from [<c0803874>] (s3c24xx_serial_shutdown+0x314/0x52c)
[<c0803874>] (s3c24xx_serial_shutdown) from [<c07f5124>] (uart_port_shutdown+0x54/0x88)
[<c07f5124>] (uart_port_shutdown) from [<c07f522c>] (uart_shutdown+0xd4/0x110)
[<c07f522c>] (uart_shutdown) from [<c07f6a8c>] (uart_hangup+0x9c/0x208)
[<c07f6a8c>] (uart_hangup) from [<c07c426c>] (__tty_hangup+0x49c/0x634)
[<c07c426c>] (__tty_hangup) from [<c07c78ac>] (tty_ioctl+0xc88/0x16e4)
[<c07c78ac>] (tty_ioctl) from [<c03b5f2c>] (do_vfs_ioctl+0xc4/0xd10)
[<c03b5f2c>] (do_vfs_ioctl) from [<c03b6bf4>] (SyS_ioctl+0x7c/0x8c)
[<c03b6bf4>] (SyS_ioctl) from [<c010b4a0>] (ret_fast_syscall+0x0/0x3c)

Reported-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Fixes: 62c37ee ("serial: samsung: add dma reqest/release functions")
CC: stable@vger.kernel.org # v4.10+
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Reviewed-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/samsung.c

@@ -859,7 +859,7 @@ static void s3c24xx_serial_break_ctl(struct uart_port *port, int break_state)
 static int s3c24xx_serial_request_dma(struct s3c24xx_uart_port *p)
 {
 	struct s3c24xx_uart_dma	*dma = p->dma;
-	unsigned long flags;
+	int ret;
 
 	/* Default slave configuration parameters */
 	dma->rx_conf.direction		= DMA_DEV_TO_MEM;
@@ -884,8 +884,8 @@ static int s3c24xx_serial_request_dma(struct s3c24xx_uart_port *p)
 
 	dma->tx_chan = dma_request_chan(p->port.dev, "tx");
 	if (IS_ERR(dma->tx_chan)) {
-		dma_release_channel(dma->rx_chan);
-		return PTR_ERR(dma->tx_chan);
+		ret = PTR_ERR(dma->tx_chan);
+		goto err_release_rx;
 	}
 
 	dmaengine_slave_config(dma->tx_chan, &dma->tx_conf);
@@ -894,15 +894,17 @@ static int s3c24xx_serial_request_dma(struct s3c24xx_uart_port *p)
 	dma->rx_size = PAGE_SIZE;
 
 	dma->rx_buf = kmalloc(dma->rx_size, GFP_KERNEL);
-
 	if (!dma->rx_buf) {
-		dma_release_channel(dma->rx_chan);
-		dma_release_channel(dma->tx_chan);
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto err_release_tx;
 	}
 
 	dma->rx_addr = dma_map_single(p->port.dev, dma->rx_buf,
 				dma->rx_size, DMA_FROM_DEVICE);
+	if (dma_mapping_error(p->port.dev, dma->rx_addr)) {
+		ret = -EIO;
+		goto err_free_rx;
+	}
 
 	spin_lock_irqsave(&p->port.lock, flags);
 
@@ -911,8 +913,23 @@ static int s3c24xx_serial_request_dma(struct s3c24xx_uart_port *p)
 				UART_XMIT_SIZE, DMA_TO_DEVICE);
 
 	spin_unlock_irqrestore(&p->port.lock, flags);
+	if (dma_mapping_error(p->port.dev, dma->tx_addr)) {
+		ret = -EIO;
+		goto err_unmap_rx;
+	}
 
 	return 0;
+
+err_unmap_rx:
+	dma_unmap_single(p->port.dev, dma->rx_addr, dma->rx_size,
+			 DMA_FROM_DEVICE);
+err_free_rx:
+	kfree(dma->rx_buf);
+err_release_tx:
+	dma_release_channel(dma->tx_chan);
+err_release_rx:
+	dma_release_channel(dma->rx_chan);
+	return ret;
 }
 
 static void s3c24xx_serial_release_dma(struct s3c24xx_uart_port *p)