Hi Wolfram,
On Thu, Sep 13, 2018 at 4:53 PM Wolfram Sang
<[email protected]> 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 <[email protected]>
> ---
>
> 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 -- [email protected]
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
