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

Masahiro Yamada
2019-08-27T09:04:09Z

On Tue, Aug 27, 2019 at 4:50 PM Christoph Hellwig <hch@lst.de> wrote:
>
> 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.

Thanks for the pointer.

> 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 */

Yes, this makes my driver working again
when CONFIG_DMA_CMA=y.

If I apply the following, my driver gets back working
irrespective of CONFIG_DMA_CMA.

diff --git a/drivers/mmc/host/sdhci-cadence.c b/drivers/mmc/host/sdhci-cadence.c
index 163d1cf4367e..504459395c39 100644
--- a/drivers/mmc/host/sdhci-cadence.c
+++ b/drivers/mmc/host/sdhci-cadence.c
@@ -237,6 +237,7 @@ static const struct sdhci_ops sdhci_cdns_ops = {

static const struct sdhci_pltfm_data sdhci_cdns_pltfm_data = {
.ops = &sdhci_cdns_ops,
+ .quirks2 = SDHCI_QUIRK2_BROKEN_64_BIT_DMA,
};

static int sdhci_cdns_set_tune_val(struct sdhci_host *host, unsigned int val)

--
Best Regards
Masahiro Yamada