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    Subject[PATCH 4.14 08/53] dmaengine: rcar-dmac: Reject zero-length slave DMA requests
    Date
    [ Upstream commit 78efb76ab4dfb8f74f290ae743f34162cd627f19 ]

    While the .device_prep_slave_sg() callback rejects empty scatterlists,
    it still accepts single-entry scatterlists with a zero-length segment.
    These may happen if a driver calls dmaengine_prep_slave_single() with a
    zero len parameter. The corresponding DMA request will never complete,
    leading to messages like:

    rcar-dmac e7300000.dma-controller: Channel Address Error happen

    and DMA timeouts.

    Although requesting a zero-length DMA request is a driver bug, rejecting
    it early eases debugging. Note that the .device_prep_dma_memcpy()
    callback already rejects requests to copy zero bytes.

    Reported-by: Eugeniu Rosca <erosca@de.adit-jv.com>
    Analyzed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
    Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
    Signed-off-by: Vinod Koul <vkoul@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/dma/sh/rcar-dmac.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
    index 77b126525daca..19c7433e83097 100644
    --- a/drivers/dma/sh/rcar-dmac.c
    +++ b/drivers/dma/sh/rcar-dmac.c
    @@ -1129,7 +1129,7 @@ rcar_dmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
    struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);

    /* Someone calling slave DMA on a generic channel? */
    - if (rchan->mid_rid < 0 || !sg_len) {
    + if (rchan->mid_rid < 0 || !sg_len || !sg_dma_len(sgl)) {
    dev_warn(chan->device->dev,
    "%s: bad parameter: len=%d, id=%d\n",
    __func__, sg_len, rchan->mid_rid);
    --
    2.20.1


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