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 <ero...@de.adit-jv.com> Analyzed-by: Yoshihiro Shimoda <yoshihiro.shimoda...@renesas.com> Signed-off-by: Geert Uytterhoeven <geert+rene...@glider.be> --- See "[PATCH 0/2] serial: sh-sci: Fix .flush_buffer() issues" (https://lore.kernel.org/linux-renesas-soc/20190624123540.20629-1-geert+rene...@glider.be/) for the driver fix. 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 67df54ac329400b7..9c41a4e425759fcc 100644 --- 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); -- 2.17.1