Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1514594 > unrolled thread

[PATCH v2] arc: Implement arch-specific dma_map_ops.mmap

Back to article view | Back to linux.kernel

Contents

  [PATCH v2] arc: Implement arch-specific dma_map_ops.mmap Alexey Brodkin <Alexey.Brodkin@synopsys.com> - 2016-11-03 16:10 +0100
    Re: [PATCH v2] arc: Implement arch-specific dma_map_ops.mmap Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2016-11-03 18:10 +0100
      RE: [PATCH v2] arc: Implement arch-specific dma_map_ops.mmap Alexey Brodkin <Alexey.Brodkin@synopsys.com> - 2016-11-04 06:40 +0100

#1514594 — [PATCH v2] arc: Implement arch-specific dma_map_ops.mmap

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>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: <stable@vger.kernel.org>
---

Changes v1 -> v2:
 * Added plat_dma_to_phys wrapper around dma_addr

 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..9288851d43a0 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(plat_dma_to_phys(dev, 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

[toc] | [next] | [standalone]

#1514705

On 11/03/2016 08:06 AM, Alexey Brodkin wrote:
> 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>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> Cc: Vineet Gupta <vgupta@synopsys.com>
> Cc: <stable@vger.kernel.org>

I've added a stable 4.5+, since ARC didn't use dma ops until 4.5-rc1.
Pushed to for-curr !

Thx,
-Vineet

> ---
> 
> Changes v1 -> v2:
>  * Added plat_dma_to_phys wrapper around dma_addr
> 
>  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..9288851d43a0 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(plat_dma_to_phys(dev, 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,
> 

[toc] | [prev] | [next] | [standalone]

#1515017

Hi Vineet,

> -----Original Message-----
> From: Vineet Gupta [mailto:vgupta@synopsys.com]
> Sent: Thursday, November 03, 2016 8:04 PM
> To: Alexey Brodkin <Alexey.Brodkin@synopsys.com>; linux-snps-arc@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org; linux-arch@vger.kernel.org; Vineet Gupta <Vineet.Gupta1@synopsys.com>; Marek Szyprowski
> <m.szyprowski@samsung.com>; stable@vger.kernel.org
> Subject: Re: [PATCH v2] arc: Implement arch-specific dma_map_ops.mmap
> 
> On 11/03/2016 08:06 AM, Alexey Brodkin wrote:
> > 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>
> > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> > Cc: Vineet Gupta <vgupta@synopsys.com>
> > Cc: <stable@vger.kernel.org>
> 
> I've added a stable 4.5+, since ARC didn't use dma ops until 4.5-rc1.

Again I was hitting a strange problem when sending patch via "git send-email" to
address "<stable@vger.kernel.org> # 3.3.x". Mail server complains on wrong email.
Thus I settled to just mention stable@vger.kernel.org.

Anyways, thanks for doing that!

-Alexey

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web