From: robin.murphy@arm•com (Robin Murphy)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] ARM64: dma-mapping: fix IOMMU-based dma_mmap_atts() implementation
Date: Tue, 16 Feb 2016 15:02:21 +0000 [thread overview]
Message-ID: <56C339FD.6040907@arm.com> (raw)
In-Reply-To: <1455632065-14620-1-git-send-email-m.szyprowski@samsung.com>
Hi Marek,
On 16/02/16 14:14, Marek Szyprowski wrote:
> IOMMU-based DMA-mapping implementation doesn't support
> dma_declare_coherent() based regions, so there is no point to call
> dma_mmap_from_coherent() from __iommu_mmap_atts(). This patch removes
> useless code.
I'm not sure that's the case - AFAICS a device could still have its own
local memory despite being behind an IOMMU relative to the rest of the
system. If it uses dma_declare_coherent() for that, the .alloc and .free
callbacks here might be bypassed by dma_{alloc,free}_attrs()
short-circuiting into dma_{alloc,release}_from_coherent(), but in the
case of dma_mmap_attrs() it hits the .mmap callback first and only falls
back to the from_coherent check in dma_common_mmap() if that isn't
implemented.
Maybe the right thing to do would be to move this check (with its
associated guards) out from dma_common_mmap() up to dma_mmap_attrs() to
be consistent with alloc/free; so that it doesn't need to be
reimplemented all over arch/{arm,arm64,mips} at all?
Robin.
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung•com>
> ---
> arch/arm64/mm/dma-mapping.c | 5 -----
> 1 file changed, 5 deletions(-)
>
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index 331c4ca..573b1e6 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -636,14 +636,9 @@ static int __iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
> struct dma_attrs *attrs)
> {
> struct vm_struct *area;
> - int ret;
>
> vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot,
> is_device_dma_coherent(dev));
> -
> - if (dma_mmap_from_coherent(dev, vma, cpu_addr, size, &ret))
> - return ret;
> -
> area = find_vm_area(cpu_addr);
> if (WARN_ON(!area || !area->pages))
> return -ENXIO;
>
next prev parent reply other threads:[~2016-02-16 15:02 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-16 14:14 [PATCH] ARM64: dma-mapping: fix IOMMU-based dma_mmap_atts() implementation Marek Szyprowski
2016-02-16 15:02 ` Robin Murphy [this message]
2016-02-17 8:55 ` Marek Szyprowski
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