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Subject[PATCH v2 30/31] stk-webcam: don't use stack for DMA
Date
From: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

The USB control messages require DMA to work. We cannot pass
a stack-allocated buffer, as it is not warranted that the
stack would be into a DMA enabled area.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
---
drivers/media/usb/stkwebcam/stk-webcam.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/media/usb/stkwebcam/stk-webcam.c b/drivers/media/usb/stkwebcam/stk-webcam.c
index db200c9d796d..22a9aae16291 100644
--- a/drivers/media/usb/stkwebcam/stk-webcam.c
+++ b/drivers/media/usb/stkwebcam/stk-webcam.c
@@ -147,20 +147,26 @@ int stk_camera_write_reg(struct stk_camera *dev, u16 index, u8 value)
int stk_camera_read_reg(struct stk_camera *dev, u16 index, int *value)
{
struct usb_device *udev = dev->udev;
+ unsigned char *buf;
int ret;

+ buf = kmalloc(sizeof(u8), GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
ret = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
0x00,
USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
0x00,
index,
- (u8 *) value,
+ buf,
sizeof(u8),
500);
- if (ret < 0)
- return ret;
- else
- return 0;
+ if (ret >= 0)
+ memcpy(value, buf, sizeof(u8));
+
+ kfree(buf);
+ return ret;
}

static int stk_start_stream(struct stk_camera *dev)
--
2.7.4

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