Hi Wolfram, On Thu, Sep 13, 2018 at 4:53 PM Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx> wrote: > Fix warning when running with CONFIG_DMA_API_DEBUG_SG=y by allocating a > device_dma_parameters structure and filling in the max segment size. > > Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx> > --- > > According to this discussion [1], this is the intended way of setting > dma_parms. I am not 100% sure about the value, though. I took the maximum value > of the DMA Transfer Count Registers which is 16M. I'd think the real maximum > needs to be multiplied with the data length which is varying, though? Geert, > what do you think? > > [1] https://www.spinics.net/lists/iommu/msg29861.html > > drivers/dma/sh/rcar-dmac.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c > index 48ee35e2bce6..bb3631f6c41c 100644 > --- a/drivers/dma/sh/rcar-dmac.c > +++ b/drivers/dma/sh/rcar-dmac.c > @@ -198,6 +198,7 @@ struct rcar_dmac { > struct dma_device engine; > struct device *dev; > void __iomem *iomem; > + struct device_dma_parameters parms; > > unsigned int n_channels; > struct rcar_dmac_chan *channels; > @@ -1792,6 +1793,8 @@ static int rcar_dmac_probe(struct platform_device *pdev) > > dmac->dev = &pdev->dev; > platform_set_drvdata(pdev, dmac); > + dmac->dev->dma_parms = &dmac->parms; > + dma_set_max_seg_size(dmac->dev, 0x01000000); That is one too much, cfr. drivers/dma/sh/rcar-dmac.c:#define RCAR_DMATCR_MASK 0x00ffffff And commit d716d9b702bb759d ("dmaengine: rcar-dmac: fix max_chunk_size for R-Car Gen3"), which did: - max_chunk_size = (RCAR_DMATCR_MASK + 1) << desc->xfer_shift; + max_chunk_size = RCAR_DMATCR_MASK << desc->xfer_shift; And yes, this depends on the data length, which is not known at probe time. Of course, dma_set_max_seg_size(dmac->dev, RCAR_DMATCR_MASK) should be safe, albeit (slightly) suboptimal. But I doubt anyone is really doing such large transfers (up to (16 Mi - 1) * 64 bytes!). > dma_set_mask_and_coherent(dmac->dev, DMA_BIT_MASK(40)); > > ret = rcar_dmac_parse_of(&pdev->dev, dmac); Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
