dmaengine: rcar-dmac: Reject zero-length slave DMA requests

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>

diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index 67df54ac329400b72d2aab9685f23876524af2fd..9c41a4e425759fcca6235e80c4ff42bf9fcb6c4b 100644 (file)
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -1165,7 +1165,7 @@ 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);