XDMA crashes on zero-length sg entries

[Martin Tůma <tumic@xxxxxxxxxx>]

Hi,
The Xilinx XDMA driver crashes when the scatterlist provided to
xdma_prep_device_sg() contains an empty entry, i.e. sg_dma_len()
returns zero. As I do get such sgl from v4l2 I suppose that this
is a valid scenario and not a bug in our parent mgb4 driver. Also
the documentation for sg_dma_len() suggests that there may be
zero-length entries.

The following trivial patch fixes the crash:

diff --git a/drivers/dma/xilinx/xdma.c b/drivers/dma/xilinx/xdma.c
index 462109c61653..cd5fcd911c50 100644
--- a/drivers/dma/xilinx/xdma.c
+++ b/drivers/dma/xilinx/xdma.c
@@ -487,6 +487,8 @@ xdma_prep_device_sg(struct dma_chan *chan, struct 
scatterlist *sgl,
        for_each_sg(sgl, sg, sg_len, i) {
                addr = sg_dma_address(sg);
                rest = sg_dma_len(sg);
+               if (!rest)
+                       break;

                do {
                        len = min_t(u32, rest, XDMA_DESC_BLEN_MAX);

M.