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SubjectRe: [RFC v2 2/2] base: dma-mapping: Postpone page_to_pfn() on mmap()
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On 14/11/17 17:08, Jacopo Mondi wrote:
> On SH4 architecture, with SPARSEMEM memory model, translating page to
> pfn hangs the CPU. Post-pone translation to pfn after
> dma_mmap_from_dev_coherent() function call as it succeeds and make page
> translation not necessary.
>
> This patch was suggested by Laurent Pinchart and he's working to submit
> a proper fix mainline. Not sending for inclusion at the moment.

Y'know, I think this patch does have some merit by itself - until we
know that cpu_addr *doesn't* represent some device-private memory which
is not guaranteed to be backed by a struct page, calling virt_to_page()
on it is arguably semantically incorrect, even if it might happen to be
benign in most cases.

Robin.

> Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> ---
> drivers/base/dma-mapping.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c
> index e584edd..73d64d3 100644
> --- a/drivers/base/dma-mapping.c
> +++ b/drivers/base/dma-mapping.c
> @@ -227,8 +227,8 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
> #ifndef CONFIG_ARCH_NO_COHERENT_DMA_MMAP
> unsigned long user_count = vma_pages(vma);
> unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> - unsigned long pfn = page_to_pfn(virt_to_page(cpu_addr));
> unsigned long off = vma->vm_pgoff;
> + unsigned long pfn;
>
> vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>
> @@ -236,6 +236,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
> return ret;
>
> if (off < count && user_count <= (count - off)) {
> + pfn = page_to_pfn(virt_to_page(cpu_addr));
> ret = remap_pfn_range(vma, vma->vm_start,
> pfn + off,
> user_count << PAGE_SHIFT,
> --
> 2.7.4
>
> _______________________________________________
> iommu mailing list
> iommu@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>

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