Re: [PATCH v2 2/2] dma-contiguous: Use fallback alloc_pages for single pages

Christoph Hellwig
2019-08-27T07:50:29Z

On Tue, Aug 27, 2019 at 04:45:20PM +0900, Masahiro Yamada wrote:
> On Mon, Aug 26, 2019 at 4:33 PM Christoph Hellwig <hch@lst.de> wrote:
> >
> > On Mon, Aug 26, 2019 at 11:05:00AM +0900, Masahiro Yamada wrote:
> > > This is included in v5.3-rc6
> > > so I tested it.
> >
> > So there is no allocation failure, but you get I/O errors later?
>
> Right.
>
> >
> > Does the device use a device-private CMA area?
>
> Not sure.
> My driver is drivers/mmc/host/sdhci-cadence.c
> It reuses routines in drivers/mmc/host/sdhci.c
>
>
>
> > Does it work with Linux
> > 5.2 if CONFIG_DMA_CMA is disabled?
>
> No.
> 5.2 + disable CONFIG_DMA_CMA
> failed in the same way.

So it seems like the device wants CMA memory. I guess the patch
below will fix it, but that isn't the solution. Can you try it
to confirm? In the end it probably assumes a dma mask it doesn't
set that the CMA memory satisfies or something similar.

diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 69cfb4345388..bd2f24aa7f19 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -236,7 +236,7 @@ struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)

if (dev && dev->cma_area)
cma = dev->cma_area;
- else if (count > 1)
+ else
cma = dma_contiguous_default_area;

/* CMA can be used only in the context which permits sleeping */