[media] em28xx: move caching of pointer to vmalloc memory in videobuf to struct em28xx_buffer

In the current code em28xx_urb_data_copy() caches the pointer to the vmalloc
memory in videobuf locally.
The alternative would be to call videobuf_to_vmalloc() for each processed USB
data packet (isoc USB transfers => 64 times per URB) in the em28xx_copy_*()
functions.
With the next commits, the data processing code will be split into functions
for serveral reasons:
- em28xx_urb_data_copy() is generally way to long, making it less readable
- there is code duplication between VBI and video data processing
- support for em25xx data processing (uses a different header and frame
  end signaling mechanism) will be added
This would require extensive usage of pointer-pointers, which usually makes the
code less readable and prone to bugs.
The better solution is to cache the pointer in struct em28xx_buffer.
This also improves consistency, because we already track the buffer fill count there.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/media/usb/em28xx/em28xx.h b/drivers/media/usb/em28xx/em28xx.h
index 7507aa6..062841e 100644
--- a/drivers/media/usb/em28xx/em28xx.h
+++ b/drivers/media/usb/em28xx/em28xx.h
@@ -258,6 +258,9 @@ struct em28xx_buffer {
 	unsigned int pos;
 	/* NOTE; in interlaced mode, this value is reset to zero at
 	 * the start of each new field (not frame !)		   */
+
+	/* pointer to vmalloc memory address in vb */
+	char *vb_buf;
 };
 
 struct em28xx_dmaqueue {