* [PATCH] arc: Implement arch-specific dma_map_ops.mmap
@ 2016-11-02 12:19 Alexey Brodkin
2016-11-02 17:08 ` Catalin Marinas
0 siblings, 1 reply; 2+ messages in thread
From: Alexey Brodkin @ 2016-11-02 12:19 UTC (permalink / raw)
To: linux-snps-arc
Cc: linux-kernel, linux-arch, Vineet Gupta, Alexey Brodkin,
Catalin Marinas, Marek Szyprowski, stable
We used to use generic implementation of dma_map_ops.mmap which is
dma_common_mmap() but that only worked for simpler cached mappings when
vaddr = paddr.
If a driver requests uncached DMA buffer kernel maps it to virtual
address so that MMU gets involved and page uncached status takes into
account. In that case usage of dma_common_mmap() lead to mapping of
vaddr to vaddr for user-space which is obviously wrong. For more detals
please refer to verbose explanation here [1].
So here we implement our own version of mmap() which always deals
with dma_addr and maps underlying memory to user-space properly
(note that DMA buffer mapped to user-space is always uncached
because there's no way to properly manage cache from user-space).
[1] https://lkml.org/lkml/2016/10/26/973
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: stable@vger.kernel.org
---
arch/arc/mm/dma.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/arch/arc/mm/dma.c b/arch/arc/mm/dma.c
index 20afc65e22dc..034ec6a8a764 100644
--- a/arch/arc/mm/dma.c
+++ b/arch/arc/mm/dma.c
@@ -105,6 +105,31 @@ static void arc_dma_free(struct device *dev, size_t size, void *vaddr,
__free_pages(page, get_order(size));
}
+static int arc_dma_mmap(struct device *dev, struct vm_area_struct *vma,
+ void *cpu_addr, dma_addr_t dma_addr, size_t size,
+ unsigned long attrs)
+{
+ unsigned long user_count = vma_pages(vma);
+ unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
+ unsigned long pfn = __phys_to_pfn(dma_addr);
+ unsigned long off = vma->vm_pgoff;
+ int ret = -ENXIO;
+
+ vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+
+ if (dma_mmap_from_coherent(dev, vma, cpu_addr, size, &ret))
+ return ret;
+
+ if (off < count && user_count <= (count - off)) {
+ ret = remap_pfn_range(vma, vma->vm_start,
+ pfn + off,
+ user_count << PAGE_SHIFT,
+ vma->vm_page_prot);
+ }
+
+ return ret;
+}
+
/*
* streaming DMA Mapping API...
* CPU accesses page via normal paddr, thus needs to explicitly made
@@ -193,6 +218,7 @@ static int arc_dma_supported(struct device *dev, u64 dma_mask)
struct dma_map_ops arc_dma_ops = {
.alloc = arc_dma_alloc,
.free = arc_dma_free,
+ .mmap = arc_dma_mmap,
.map_page = arc_dma_map_page,
.map_sg = arc_dma_map_sg,
.sync_single_for_device = arc_dma_sync_single_for_device,
--
2.7.4
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] arc: Implement arch-specific dma_map_ops.mmap
2016-11-02 12:19 [PATCH] arc: Implement arch-specific dma_map_ops.mmap Alexey Brodkin
@ 2016-11-02 17:08 ` Catalin Marinas
0 siblings, 0 replies; 2+ messages in thread
From: Catalin Marinas @ 2016-11-02 17:08 UTC (permalink / raw)
To: Alexey Brodkin
Cc: linux-snps-arc, linux-kernel, linux-arch, Vineet Gupta,
Marek Szyprowski, stable
On Wed, Nov 02, 2016 at 03:19:43PM +0300, Alexey Brodkin wrote:
> diff --git a/arch/arc/mm/dma.c b/arch/arc/mm/dma.c
> index 20afc65e22dc..034ec6a8a764 100644
> --- a/arch/arc/mm/dma.c
> +++ b/arch/arc/mm/dma.c
> @@ -105,6 +105,31 @@ static void arc_dma_free(struct device *dev, size_t size, void *vaddr,
> __free_pages(page, get_order(size));
> }
>
> +static int arc_dma_mmap(struct device *dev, struct vm_area_struct *vma,
> + void *cpu_addr, dma_addr_t dma_addr, size_t size,
> + unsigned long attrs)
> +{
> + unsigned long user_count = vma_pages(vma);
> + unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> + unsigned long pfn = __phys_to_pfn(dma_addr);
I don't think that's correct in all situations. Better as (for arc):
unsigned long pfn = __phys_to_pfn(plat_dma_to_phys(dma_addr));
Other than that:
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
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