On Thu, Sep 27, 2018 at 3:38 PM Christoph Hellwig <h...@lst.de> wrote:
>
> This way an architecture with less than 4G of RAM can support dma_mask
> smaller than 32-bit without a ZONE_DMA. Apparently that is a common
> case on powerpc.
>
> Signed-off-by: Christoph Hellwig <h...@lst.de>
> Reviewed-by: Robin Murphy <robin.mur...@arm.com>
> ---
> kernel/dma/direct.c | 28 ++++++++++++++++------------
> 1 file changed, 16 insertions(+), 12 deletions(-)
>
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 60c433b880e0..170bd322a94a 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -284,21 +284,25 @@ int dma_direct_map_sg(struct device *dev, struct
> scatterlist *sgl, int nents,
> return nents;
> }
>
> +/*
> + * Because 32-bit DMA masks are so common we expect every architecture to be
> + * able to satisfy them - either by not supporting more physical memory, or
> by
> + * providing a ZONE_DMA32. If neither is the case, the architecture needs to
> + * use an IOMMU instead of the direct mapping.
> + */
> int dma_direct_supported(struct device *dev, u64 mask)
> {
> -#ifdef CONFIG_ZONE_DMA
> - if (mask < phys_to_dma(dev, DMA_BIT_MASK(ARCH_ZONE_DMA_BITS)))
> - return 0;
> -#else
> - /*
> - * Because 32-bit DMA masks are so common we expect every architecture
> - * to be able to satisfy them - either by not supporting more physical
> - * memory, or by providing a ZONE_DMA32. If neither is the case, the
> - * architecture needs to use an IOMMU instead of the direct mapping.
> - */
> - if (mask < phys_to_dma(dev, DMA_BIT_MASK(32)))
> + u64 min_mask;
> +
> + if (IS_ENABLED(CONFIG_ZONE_DMA))
> + min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS);
> + else
> + min_mask = DMA_BIT_MASK(32);
> +
> + min_mask = min_t(u64, min_mask, (max_pfn - 1) << PAGE_SHIFT);
> +
> + if (mask >= phys_to_dma(dev, min_mask))
> return 0;
> -#endif
> return 1;
> }
So I believe I have run into the same issue that Guenter reported. On
an x86_64 system w/ Intel IOMMU. I wasn't able to complete boot and
all probe attempts for various devices were failing with -EIO errors.
I believe the last mask check should be "if (mask < phys_to_dma(dev,
min_mask))" not a ">=" check.
- Alex
