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* fix a layering violation in videobuf2 and improve dma_map_resource
@ 2019-01-11 18:17 ` Christoph Hellwig
  2019-01-11 18:17   ` [PATCH 1/3] dma-mapping: remove the default map_resource implementation Christoph Hellwig
                     ` (3 more replies)
  0 siblings, 4 replies; 16+ messages in thread
From: Christoph Hellwig @ 2019-01-11 18:17 UTC (permalink / raw)
  To: Pawel Osciak, Marek Szyprowski, Kyungmin Park, Niklas Söderlund
  Cc: Russell King, linux-kernel, iommu, Mauro Carvalho Chehab,
	linuxppc-dev, linux-arm-kernel, linux-media

Hi all,

this series fixes a rather gross layering violation in videobuf2, which
pokes into arm DMA mapping internals to get a DMA address for memory that
does not have a page structure, and to do so fixes up the dma_map_resource
implementation to be practically useful.

^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH 1/3] dma-mapping: remove the default map_resource implementation
  2019-01-11 18:17 ` fix a layering violation in videobuf2 and improve dma_map_resource Christoph Hellwig
@ 2019-01-11 18:17   ` Christoph Hellwig
  2019-01-14 13:12     ` Robin Murphy
  2019-01-11 18:17   ` [PATCH 2/3] dma-mapping: don't BUG when calling dma_map_resource on RAM Christoph Hellwig
                     ` (2 subsequent siblings)
  3 siblings, 1 reply; 16+ messages in thread
From: Christoph Hellwig @ 2019-01-11 18:17 UTC (permalink / raw)
  To: Pawel Osciak, Marek Szyprowski, Kyungmin Park, Niklas Söderlund
  Cc: Russell King, linux-kernel, iommu, Mauro Carvalho Chehab,
	linuxppc-dev, linux-arm-kernel, linux-media

Just returning the physical address when not map_resource method is
present is highly dangerous as it doesn't take any offset in the
direct mapping into account and does the completely wrong thing for
IOMMUs.  Instead provide a proper implementation in the direct mapping
code, and also wire it up for arm and powerpc.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 arch/arm/mm/dma-mapping.c         |  2 ++
 arch/powerpc/kernel/dma-swiotlb.c |  1 +
 arch/powerpc/kernel/dma.c         |  1 +
 include/linux/dma-mapping.h       | 12 +++++++-----
 kernel/dma/direct.c               | 14 ++++++++++++++
 5 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index f1e2922e447c..3c8534904209 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -188,6 +188,7 @@ const struct dma_map_ops arm_dma_ops = {
 	.unmap_page		= arm_dma_unmap_page,
 	.map_sg			= arm_dma_map_sg,
 	.unmap_sg		= arm_dma_unmap_sg,
+	.map_resource		= dma_direct_map_resource,
 	.sync_single_for_cpu	= arm_dma_sync_single_for_cpu,
 	.sync_single_for_device	= arm_dma_sync_single_for_device,
 	.sync_sg_for_cpu	= arm_dma_sync_sg_for_cpu,
@@ -211,6 +212,7 @@ const struct dma_map_ops arm_coherent_dma_ops = {
 	.get_sgtable		= arm_dma_get_sgtable,
 	.map_page		= arm_coherent_dma_map_page,
 	.map_sg			= arm_dma_map_sg,
+	.map_resource		= dma_direct_map_resource,
 	.dma_supported		= arm_dma_supported,
 };
 EXPORT_SYMBOL(arm_coherent_dma_ops);
diff --git a/arch/powerpc/kernel/dma-swiotlb.c b/arch/powerpc/kernel/dma-swiotlb.c
index 7d5fc9751622..fbb2506a414e 100644
--- a/arch/powerpc/kernel/dma-swiotlb.c
+++ b/arch/powerpc/kernel/dma-swiotlb.c
@@ -55,6 +55,7 @@ const struct dma_map_ops powerpc_swiotlb_dma_ops = {
 	.dma_supported = swiotlb_dma_supported,
 	.map_page = dma_direct_map_page,
 	.unmap_page = dma_direct_unmap_page,
+	.map_resource = dma_direct_map_resource,
 	.sync_single_for_cpu = dma_direct_sync_single_for_cpu,
 	.sync_single_for_device = dma_direct_sync_single_for_device,
 	.sync_sg_for_cpu = dma_direct_sync_sg_for_cpu,
diff --git a/arch/powerpc/kernel/dma.c b/arch/powerpc/kernel/dma.c
index b1903ebb2e9c..258b9e8ebb99 100644
--- a/arch/powerpc/kernel/dma.c
+++ b/arch/powerpc/kernel/dma.c
@@ -273,6 +273,7 @@ const struct dma_map_ops dma_nommu_ops = {
 	.dma_supported			= dma_nommu_dma_supported,
 	.map_page			= dma_nommu_map_page,
 	.unmap_page			= dma_nommu_unmap_page,
+	.map_resource			= dma_direct_map_resource,
 	.get_required_mask		= dma_nommu_get_required_mask,
 #ifdef CONFIG_NOT_COHERENT_CACHE
 	.sync_single_for_cpu 		= dma_nommu_sync_single,
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index cef2127e1d70..d3087829a6df 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -208,6 +208,8 @@ dma_addr_t dma_direct_map_page(struct device *dev, struct page *page,
 		unsigned long attrs);
 int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
 		enum dma_data_direction dir, unsigned long attrs);
+dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,
+		size_t size, enum dma_data_direction dir, unsigned long attrs);
 
 #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
     defined(CONFIG_SWIOTLB)
@@ -346,19 +348,19 @@ static inline dma_addr_t dma_map_resource(struct device *dev,
 					  unsigned long attrs)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
-	dma_addr_t addr;
+	dma_addr_t addr = DMA_MAPPING_ERROR;
 
 	BUG_ON(!valid_dma_direction(dir));
 
 	/* Don't allow RAM to be mapped */
 	BUG_ON(pfn_valid(PHYS_PFN(phys_addr)));
 
-	addr = phys_addr;
-	if (ops && ops->map_resource)
+	if (dma_is_direct(ops))
+		addr = dma_direct_map_resource(dev, phys_addr, size, dir, attrs);
+	else if (ops->map_resource)
 		addr = ops->map_resource(dev, phys_addr, size, dir, attrs);
 
 	debug_dma_map_resource(dev, phys_addr, size, dir, addr);
-
 	return addr;
 }
 
@@ -369,7 +371,7 @@ static inline void dma_unmap_resource(struct device *dev, dma_addr_t addr,
 	const struct dma_map_ops *ops = get_dma_ops(dev);
 
 	BUG_ON(!valid_dma_direction(dir));
-	if (ops && ops->unmap_resource)
+	if (!dma_is_direct(ops) && ops->unmap_resource)
 		ops->unmap_resource(dev, addr, size, dir, attrs);
 	debug_dma_unmap_resource(dev, addr, size, dir);
 }
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 355d16acee6d..8e0359b04957 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -356,6 +356,20 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
 }
 EXPORT_SYMBOL(dma_direct_map_sg);
 
+dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,
+		size_t size, enum dma_data_direction dir, unsigned long attrs)
+{
+	dma_addr_t dma_addr = phys_to_dma(dev, paddr);
+
+	if (unlikely(!dma_direct_possible(dev, dma_addr, size))) {
+		report_addr(dev, dma_addr, size);
+		return DMA_MAPPING_ERROR;
+	}
+
+	return dma_addr;
+}
+EXPORT_SYMBOL(dma_direct_map_resource);
+
 /*
  * 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
-- 
2.20.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH 2/3] dma-mapping: don't BUG when calling dma_map_resource on RAM
  2019-01-11 18:17 ` fix a layering violation in videobuf2 and improve dma_map_resource Christoph Hellwig
  2019-01-11 18:17   ` [PATCH 1/3] dma-mapping: remove the default map_resource implementation Christoph Hellwig
@ 2019-01-11 18:17   ` Christoph Hellwig
  2019-01-14 14:16     ` Robin Murphy
  2019-01-11 18:17   ` [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource Christoph Hellwig
  2019-01-14 11:43   ` fix a layering violation in videobuf2 and improve dma_map_resource Marek Szyprowski
  3 siblings, 1 reply; 16+ messages in thread
From: Christoph Hellwig @ 2019-01-11 18:17 UTC (permalink / raw)
  To: Pawel Osciak, Marek Szyprowski, Kyungmin Park, Niklas Söderlund
  Cc: Russell King, linux-kernel, iommu, Mauro Carvalho Chehab,
	linuxppc-dev, linux-arm-kernel, linux-media

Use WARN_ON_ONCE to print a stack trace and return a proper error
code instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/dma-mapping.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index d3087829a6df..91add0751aa5 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -353,7 +353,8 @@ static inline dma_addr_t dma_map_resource(struct device *dev,
 	BUG_ON(!valid_dma_direction(dir));
 
 	/* Don't allow RAM to be mapped */
-	BUG_ON(pfn_valid(PHYS_PFN(phys_addr)));
+	if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr))))
+		return DMA_MAPPING_ERROR;
 
 	if (dma_is_direct(ops))
 		addr = dma_direct_map_resource(dev, phys_addr, size, dir, attrs);
-- 
2.20.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource
  2019-01-11 18:17 ` fix a layering violation in videobuf2 and improve dma_map_resource Christoph Hellwig
  2019-01-11 18:17   ` [PATCH 1/3] dma-mapping: remove the default map_resource implementation Christoph Hellwig
  2019-01-11 18:17   ` [PATCH 2/3] dma-mapping: don't BUG when calling dma_map_resource on RAM Christoph Hellwig
@ 2019-01-11 18:17   ` Christoph Hellwig
  2019-01-11 19:54     ` Mauro Carvalho Chehab
  2019-01-14 12:42     ` Marek Szyprowski
  2019-01-14 11:43   ` fix a layering violation in videobuf2 and improve dma_map_resource Marek Szyprowski
  3 siblings, 2 replies; 16+ messages in thread
From: Christoph Hellwig @ 2019-01-11 18:17 UTC (permalink / raw)
  To: Pawel Osciak, Marek Szyprowski, Kyungmin Park, Niklas Söderlund
  Cc: Russell King, linux-kernel, iommu, Mauro Carvalho Chehab,
	linuxppc-dev, linux-arm-kernel, linux-media

vb2_dc_get_userptr pokes into arm direct mapping details to get the
resemblance of a dma address for a a physical address that does is
not backed by a page struct.  Not only is this not portable to other
architectures with dma direct mapping offsets, but also not to uses
of IOMMUs of any kind.  Switch to the proper dma_map_resource /
dma_unmap_resource interface instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 .../common/videobuf2/videobuf2-dma-contig.c   | 41 ++++---------------
 1 file changed, 9 insertions(+), 32 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
index aff0ab7bf83d..82389aead6ed 100644
--- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
+++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
@@ -439,42 +439,14 @@ static void vb2_dc_put_userptr(void *buf_priv)
 				set_page_dirty_lock(pages[i]);
 		sg_free_table(sgt);
 		kfree(sgt);
+	} else {
+		dma_unmap_resource(buf->dev, buf->dma_addr, buf->size,
+				   buf->dma_dir, 0);
 	}
 	vb2_destroy_framevec(buf->vec);
 	kfree(buf);
 }
 
-/*
- * For some kind of reserved memory there might be no struct page available,
- * so all that can be done to support such 'pages' is to try to convert
- * pfn to dma address or at the last resort just assume that
- * dma address == physical address (like it has been assumed in earlier version
- * of videobuf2-dma-contig
- */
-
-#ifdef __arch_pfn_to_dma
-static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
-{
-	return (dma_addr_t)__arch_pfn_to_dma(dev, pfn);
-}
-#elif defined(__pfn_to_bus)
-static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
-{
-	return (dma_addr_t)__pfn_to_bus(pfn);
-}
-#elif defined(__pfn_to_phys)
-static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
-{
-	return (dma_addr_t)__pfn_to_phys(pfn);
-}
-#else
-static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
-{
-	/* really, we cannot do anything better at this point */
-	return (dma_addr_t)(pfn) << PAGE_SHIFT;
-}
-#endif
-
 static void *vb2_dc_get_userptr(struct device *dev, unsigned long vaddr,
 	unsigned long size, enum dma_data_direction dma_dir)
 {
@@ -528,7 +500,12 @@ static void *vb2_dc_get_userptr(struct device *dev, unsigned long vaddr,
 		for (i = 1; i < n_pages; i++)
 			if (nums[i-1] + 1 != nums[i])
 				goto fail_pfnvec;
-		buf->dma_addr = vb2_dc_pfn_to_dma(buf->dev, nums[0]);
+		buf->dma_addr = dma_map_resource(buf->dev,
+				__pfn_to_phys(nums[0]), size, buf->dma_dir, 0);
+		if (dma_mapping_error(buf->dev, buf->dma_addr)) {
+			ret = -ENOMEM;
+			goto fail_pfnvec;
+		}
 		goto out;
 	}
 
-- 
2.20.1


^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource
  2019-01-11 18:17   ` [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource Christoph Hellwig
@ 2019-01-11 19:54     ` Mauro Carvalho Chehab
  2019-01-14 10:31       ` Christoph Hellwig
  2019-01-14 12:42     ` Marek Szyprowski
  1 sibling, 1 reply; 16+ messages in thread
From: Mauro Carvalho Chehab @ 2019-01-11 19:54 UTC (permalink / raw)
  To: Christoph Hellwig
  Cc: Niklas Söderlund, Pawel Osciak, Russell King, iommu,
	linux-kernel, Kyungmin Park, linux-media, linuxppc-dev,
	linux-arm-kernel, Marek Szyprowski

Em Fri, 11 Jan 2019 19:17:31 +0100
Christoph Hellwig <hch@lst.de> escreveu:

> vb2_dc_get_userptr pokes into arm direct mapping details to get the
> resemblance of a dma address for a a physical address that does is
> not backed by a page struct.  Not only is this not portable to other
> architectures with dma direct mapping offsets, but also not to uses
> of IOMMUs of any kind.  Switch to the proper dma_map_resource /
> dma_unmap_resource interface instead.

Makes sense to me. I'm assuming that you'll be pushing it together
with other mm patches, so:

Acked-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  .../common/videobuf2/videobuf2-dma-contig.c   | 41 ++++---------------
>  1 file changed, 9 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> index aff0ab7bf83d..82389aead6ed 100644
> --- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> +++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> @@ -439,42 +439,14 @@ static void vb2_dc_put_userptr(void *buf_priv)
>  				set_page_dirty_lock(pages[i]);
>  		sg_free_table(sgt);
>  		kfree(sgt);
> +	} else {
> +		dma_unmap_resource(buf->dev, buf->dma_addr, buf->size,
> +				   buf->dma_dir, 0);
>  	}
>  	vb2_destroy_framevec(buf->vec);
>  	kfree(buf);
>  }
>  
> -/*
> - * For some kind of reserved memory there might be no struct page available,
> - * so all that can be done to support such 'pages' is to try to convert
> - * pfn to dma address or at the last resort just assume that
> - * dma address == physical address (like it has been assumed in earlier version
> - * of videobuf2-dma-contig
> - */
> -
> -#ifdef __arch_pfn_to_dma
> -static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
> -{
> -	return (dma_addr_t)__arch_pfn_to_dma(dev, pfn);
> -}
> -#elif defined(__pfn_to_bus)
> -static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
> -{
> -	return (dma_addr_t)__pfn_to_bus(pfn);
> -}
> -#elif defined(__pfn_to_phys)
> -static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
> -{
> -	return (dma_addr_t)__pfn_to_phys(pfn);
> -}
> -#else
> -static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
> -{
> -	/* really, we cannot do anything better at this point */
> -	return (dma_addr_t)(pfn) << PAGE_SHIFT;
> -}
> -#endif
> -
>  static void *vb2_dc_get_userptr(struct device *dev, unsigned long vaddr,
>  	unsigned long size, enum dma_data_direction dma_dir)
>  {
> @@ -528,7 +500,12 @@ static void *vb2_dc_get_userptr(struct device *dev, unsigned long vaddr,
>  		for (i = 1; i < n_pages; i++)
>  			if (nums[i-1] + 1 != nums[i])
>  				goto fail_pfnvec;
> -		buf->dma_addr = vb2_dc_pfn_to_dma(buf->dev, nums[0]);
> +		buf->dma_addr = dma_map_resource(buf->dev,
> +				__pfn_to_phys(nums[0]), size, buf->dma_dir, 0);
> +		if (dma_mapping_error(buf->dev, buf->dma_addr)) {
> +			ret = -ENOMEM;
> +			goto fail_pfnvec;
> +		}
>  		goto out;
>  	}
>  



Thanks,
Mauro

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource
  2019-01-11 19:54     ` Mauro Carvalho Chehab
@ 2019-01-14 10:31       ` Christoph Hellwig
  2019-01-14 11:04         ` Mauro Carvalho Chehab
  0 siblings, 1 reply; 16+ messages in thread
From: Christoph Hellwig @ 2019-01-14 10:31 UTC (permalink / raw)
  To: Mauro Carvalho Chehab
  Cc: Niklas Söderlund, Pawel Osciak, Russell King, iommu,
	linux-kernel, Kyungmin Park, linux-media, linuxppc-dev,
	Christoph Hellwig, linux-arm-kernel, Marek Szyprowski

On Fri, Jan 11, 2019 at 05:54:16PM -0200, Mauro Carvalho Chehab wrote:
> Em Fri, 11 Jan 2019 19:17:31 +0100
> Christoph Hellwig <hch@lst.de> escreveu:
> 
> > vb2_dc_get_userptr pokes into arm direct mapping details to get the
> > resemblance of a dma address for a a physical address that does is
> > not backed by a page struct.  Not only is this not portable to other
> > architectures with dma direct mapping offsets, but also not to uses
> > of IOMMUs of any kind.  Switch to the proper dma_map_resource /
> > dma_unmap_resource interface instead.
> 
> Makes sense to me. I'm assuming that you'll be pushing it together
> with other mm patches, so:

Not really mm, but rather DMA mapping, but yes, I'd love to take it
all together.

Thanks!

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource
  2019-01-14 10:31       ` Christoph Hellwig
@ 2019-01-14 11:04         ` Mauro Carvalho Chehab
  2019-01-14 11:12           ` Christoph Hellwig
  0 siblings, 1 reply; 16+ messages in thread
From: Mauro Carvalho Chehab @ 2019-01-14 11:04 UTC (permalink / raw)
  To: Christoph Hellwig
  Cc: Niklas Söderlund, Pawel Osciak, Russell King, iommu,
	linux-kernel, Kyungmin Park, linux-media, linuxppc-dev,
	linux-arm-kernel, Marek Szyprowski

Em Mon, 14 Jan 2019 11:31:39 +0100
Christoph Hellwig <hch@lst.de> escreveu:

> On Fri, Jan 11, 2019 at 05:54:16PM -0200, Mauro Carvalho Chehab wrote:
> > Em Fri, 11 Jan 2019 19:17:31 +0100
> > Christoph Hellwig <hch@lst.de> escreveu:
> >   
> > > vb2_dc_get_userptr pokes into arm direct mapping details to get the
> > > resemblance of a dma address for a a physical address that does is
> > > not backed by a page struct.  Not only is this not portable to other
> > > architectures with dma direct mapping offsets, but also not to uses
> > > of IOMMUs of any kind.  Switch to the proper dma_map_resource /
> > > dma_unmap_resource interface instead.  
> > 
> > Makes sense to me. I'm assuming that you'll be pushing it together
> > with other mm patches, so:  
> 
> Not really mm, but rather DMA mapping, but yes, I'd love to take it
> all together.

Ah, OK! Anyway, feel free to place it altogether. 

It would be good if you could later send us a stable branch where
you merged, in order to allow us to run some tests with the new
DMA mapping patchset and be sure that it won't cause regressions
to videobuf2.

Thank you!

Mauro

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource
  2019-01-14 11:04         ` Mauro Carvalho Chehab
@ 2019-01-14 11:12           ` Christoph Hellwig
  0 siblings, 0 replies; 16+ messages in thread
From: Christoph Hellwig @ 2019-01-14 11:12 UTC (permalink / raw)
  To: Mauro Carvalho Chehab
  Cc: Niklas Söderlund, Pawel Osciak, Russell King, iommu,
	linux-kernel, Kyungmin Park, linux-media, linuxppc-dev,
	Christoph Hellwig, linux-arm-kernel, Marek Szyprowski

On Mon, Jan 14, 2019 at 09:04:56AM -0200, Mauro Carvalho Chehab wrote:
> It would be good if you could later send us a stable branch where
> you merged, in order to allow us to run some tests with the new
> DMA mapping patchset and be sure that it won't cause regressions
> to videobuf2.

I can do that, but the series as sent should be testable, results
welcome!

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: fix a layering violation in videobuf2 and improve dma_map_resource
  2019-01-11 18:17 ` fix a layering violation in videobuf2 and improve dma_map_resource Christoph Hellwig
                     ` (2 preceding siblings ...)
  2019-01-11 18:17   ` [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource Christoph Hellwig
@ 2019-01-14 11:43   ` Marek Szyprowski
  3 siblings, 0 replies; 16+ messages in thread
From: Marek Szyprowski @ 2019-01-14 11:43 UTC (permalink / raw)
  To: Christoph Hellwig, Pawel Osciak, Kyungmin Park, Niklas Söderlund
  Cc: Russell King, linux-kernel, iommu, Mauro Carvalho Chehab,
	linuxppc-dev, linux-arm-kernel, linux-media

Hi Christoph,

On 2019-01-11 19:17, Christoph Hellwig wrote:
> Hi all,
>
> this series fixes a rather gross layering violation in videobuf2, which
> pokes into arm DMA mapping internals to get a DMA address for memory that
> does not have a page structure, and to do so fixes up the dma_map_resource
> implementation to be practically useful.

Thanks for rewriting this 'temporary code'! It predates
dma_map_resource() and that time this was the only way to get it working
somehow. Good that now it is possible to implement in it a clean way
without any unwritten assumptions about the DMA mapping internals. Feel
free to add my:

Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland


^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource
  2019-01-11 18:17   ` [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource Christoph Hellwig
  2019-01-11 19:54     ` Mauro Carvalho Chehab
@ 2019-01-14 12:42     ` Marek Szyprowski
  2019-01-17 17:21       ` Christoph Hellwig
  1 sibling, 1 reply; 16+ messages in thread
From: Marek Szyprowski @ 2019-01-14 12:42 UTC (permalink / raw)
  To: Christoph Hellwig, Pawel Osciak, Kyungmin Park, Niklas Söderlund
  Cc: Russell King, linux-kernel, iommu, Mauro Carvalho Chehab,
	linuxppc-dev, linux-arm-kernel, linux-media

Hi Christoph,

On 2019-01-11 19:17, Christoph Hellwig wrote:
> vb2_dc_get_userptr pokes into arm direct mapping details to get the
> resemblance of a dma address for a a physical address that does is
> not backed by a page struct.  Not only is this not portable to other
> architectures with dma direct mapping offsets, but also not to uses
> of IOMMUs of any kind.  Switch to the proper dma_map_resource /
> dma_unmap_resource interface instead.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

There are checks for IOMMU presence in other places in vb2-dma-contig,
so it was used only when no IOMMU is available, but I agree that the
hacky code should be replaced by a generic code if possible.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

V4L2 pipeline works fine on older Exynos-based boards with CMA and IOMMU
disabled.

> ---
>  .../common/videobuf2/videobuf2-dma-contig.c   | 41 ++++---------------
>  1 file changed, 9 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> index aff0ab7bf83d..82389aead6ed 100644
> --- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> +++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> @@ -439,42 +439,14 @@ static void vb2_dc_put_userptr(void *buf_priv)
>  				set_page_dirty_lock(pages[i]);
>  		sg_free_table(sgt);
>  		kfree(sgt);
> +	} else {
> +		dma_unmap_resource(buf->dev, buf->dma_addr, buf->size,
> +				   buf->dma_dir, 0);
>  	}
>  	vb2_destroy_framevec(buf->vec);
>  	kfree(buf);
>  }
>  
> -/*
> - * For some kind of reserved memory there might be no struct page available,
> - * so all that can be done to support such 'pages' is to try to convert
> - * pfn to dma address or at the last resort just assume that
> - * dma address == physical address (like it has been assumed in earlier version
> - * of videobuf2-dma-contig
> - */
> -
> -#ifdef __arch_pfn_to_dma
> -static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
> -{
> -	return (dma_addr_t)__arch_pfn_to_dma(dev, pfn);
> -}
> -#elif defined(__pfn_to_bus)
> -static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
> -{
> -	return (dma_addr_t)__pfn_to_bus(pfn);
> -}
> -#elif defined(__pfn_to_phys)
> -static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
> -{
> -	return (dma_addr_t)__pfn_to_phys(pfn);
> -}
> -#else
> -static inline dma_addr_t vb2_dc_pfn_to_dma(struct device *dev, unsigned long pfn)
> -{
> -	/* really, we cannot do anything better at this point */
> -	return (dma_addr_t)(pfn) << PAGE_SHIFT;
> -}
> -#endif
> -
>  static void *vb2_dc_get_userptr(struct device *dev, unsigned long vaddr,
>  	unsigned long size, enum dma_data_direction dma_dir)
>  {
> @@ -528,7 +500,12 @@ static void *vb2_dc_get_userptr(struct device *dev, unsigned long vaddr,
>  		for (i = 1; i < n_pages; i++)
>  			if (nums[i-1] + 1 != nums[i])
>  				goto fail_pfnvec;
> -		buf->dma_addr = vb2_dc_pfn_to_dma(buf->dev, nums[0]);
> +		buf->dma_addr = dma_map_resource(buf->dev,
> +				__pfn_to_phys(nums[0]), size, buf->dma_dir, 0);
> +		if (dma_mapping_error(buf->dev, buf->dma_addr)) {
> +			ret = -ENOMEM;
> +			goto fail_pfnvec;
> +		}
>  		goto out;
>  	}
>  

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland


^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH 1/3] dma-mapping: remove the default map_resource implementation
  2019-01-11 18:17   ` [PATCH 1/3] dma-mapping: remove the default map_resource implementation Christoph Hellwig
@ 2019-01-14 13:12     ` Robin Murphy
  2019-01-14 17:08       ` Christoph Hellwig
  0 siblings, 1 reply; 16+ messages in thread
From: Robin Murphy @ 2019-01-14 13:12 UTC (permalink / raw)
  To: Christoph Hellwig, Pawel Osciak, Marek Szyprowski, Kyungmin Park,
	Niklas Söderlund
  Cc: Russell King, linux-kernel, iommu, Mauro Carvalho Chehab,
	linuxppc-dev, linux-arm-kernel, linux-media

On 11/01/2019 18:17, Christoph Hellwig wrote:
> Just returning the physical address when not map_resource method is
> present is highly dangerous as it doesn't take any offset in the
> direct mapping into account and does the completely wrong thing for
> IOMMUs.  Instead provide a proper implementation in the direct mapping
> code, and also wire it up for arm and powerpc.

Ignoring the offset was kind of intentional there, because at the time I 
was primarily thinking about it in terms of the Keystone 2 platform 
where the peripherals are all in the same place (0-2GB) in both the bus 
and CPU physical address maps, and only the view of RAM differs between 
the two (2-4GB vs. 32-34GB). However, on something like BCM283x, the 
peripherals region is also offset from its bus address in the CPU view, 
but at a *different* offset relative to that of RAM.

Fortunately, I'm not aware of any platform which has a DMA engine behind 
an IOMMU (and thus *needs* to use dma_map_resource() to avoid said IOMMU 
blocking the slave device register reads/writes) and also has any 
nonzero offsets, and AFAIK the IOMMU-less platforms above aren't using 
dma_map_resource() at all, so this change shouldn't actually break 
anything, but I guess we have a bit of a problem making it truly generic 
and robust :(

Is this perhaps another shove in the direction of overhauling 
dma_pfn_offset into an arbitrary "DMA ranges" lookup table?

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   arch/arm/mm/dma-mapping.c         |  2 ++
>   arch/powerpc/kernel/dma-swiotlb.c |  1 +
>   arch/powerpc/kernel/dma.c         |  1 +
>   include/linux/dma-mapping.h       | 12 +++++++-----
>   kernel/dma/direct.c               | 14 ++++++++++++++
>   5 files changed, 25 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index f1e2922e447c..3c8534904209 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -188,6 +188,7 @@ const struct dma_map_ops arm_dma_ops = {
>   	.unmap_page		= arm_dma_unmap_page,
>   	.map_sg			= arm_dma_map_sg,
>   	.unmap_sg		= arm_dma_unmap_sg,
> +	.map_resource		= dma_direct_map_resource,
>   	.sync_single_for_cpu	= arm_dma_sync_single_for_cpu,
>   	.sync_single_for_device	= arm_dma_sync_single_for_device,
>   	.sync_sg_for_cpu	= arm_dma_sync_sg_for_cpu,
> @@ -211,6 +212,7 @@ const struct dma_map_ops arm_coherent_dma_ops = {
>   	.get_sgtable		= arm_dma_get_sgtable,
>   	.map_page		= arm_coherent_dma_map_page,
>   	.map_sg			= arm_dma_map_sg,
> +	.map_resource		= dma_direct_map_resource,
>   	.dma_supported		= arm_dma_supported,
>   };
>   EXPORT_SYMBOL(arm_coherent_dma_ops);
> diff --git a/arch/powerpc/kernel/dma-swiotlb.c b/arch/powerpc/kernel/dma-swiotlb.c
> index 7d5fc9751622..fbb2506a414e 100644
> --- a/arch/powerpc/kernel/dma-swiotlb.c
> +++ b/arch/powerpc/kernel/dma-swiotlb.c
> @@ -55,6 +55,7 @@ const struct dma_map_ops powerpc_swiotlb_dma_ops = {
>   	.dma_supported = swiotlb_dma_supported,
>   	.map_page = dma_direct_map_page,
>   	.unmap_page = dma_direct_unmap_page,
> +	.map_resource = dma_direct_map_resource,
>   	.sync_single_for_cpu = dma_direct_sync_single_for_cpu,
>   	.sync_single_for_device = dma_direct_sync_single_for_device,
>   	.sync_sg_for_cpu = dma_direct_sync_sg_for_cpu,
> diff --git a/arch/powerpc/kernel/dma.c b/arch/powerpc/kernel/dma.c
> index b1903ebb2e9c..258b9e8ebb99 100644
> --- a/arch/powerpc/kernel/dma.c
> +++ b/arch/powerpc/kernel/dma.c
> @@ -273,6 +273,7 @@ const struct dma_map_ops dma_nommu_ops = {
>   	.dma_supported			= dma_nommu_dma_supported,
>   	.map_page			= dma_nommu_map_page,
>   	.unmap_page			= dma_nommu_unmap_page,
> +	.map_resource			= dma_direct_map_resource,
>   	.get_required_mask		= dma_nommu_get_required_mask,
>   #ifdef CONFIG_NOT_COHERENT_CACHE
>   	.sync_single_for_cpu 		= dma_nommu_sync_single,
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index cef2127e1d70..d3087829a6df 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -208,6 +208,8 @@ dma_addr_t dma_direct_map_page(struct device *dev, struct page *page,
>   		unsigned long attrs);
>   int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
>   		enum dma_data_direction dir, unsigned long attrs);
> +dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,
> +		size_t size, enum dma_data_direction dir, unsigned long attrs);
>   
>   #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
>       defined(CONFIG_SWIOTLB)
> @@ -346,19 +348,19 @@ static inline dma_addr_t dma_map_resource(struct device *dev,
>   					  unsigned long attrs)
>   {
>   	const struct dma_map_ops *ops = get_dma_ops(dev);
> -	dma_addr_t addr;
> +	dma_addr_t addr = DMA_MAPPING_ERROR;
>   
>   	BUG_ON(!valid_dma_direction(dir));
>   
>   	/* Don't allow RAM to be mapped */
>   	BUG_ON(pfn_valid(PHYS_PFN(phys_addr)));
>   
> -	addr = phys_addr;
> -	if (ops && ops->map_resource)
> +	if (dma_is_direct(ops))
> +		addr = dma_direct_map_resource(dev, phys_addr, size, dir, attrs);
> +	else if (ops->map_resource)
>   		addr = ops->map_resource(dev, phys_addr, size, dir, attrs);

Might it be reasonable to do:

	if (!dma_is_direct(ops) && ops->map_resource)
		addr = ops->map_resource(...);
	else
		addr = dma_direct_map_resource(...);

and avoid having to explicitly wire up the dma_direct callback elsewhere?

Robin.

>   
>   	debug_dma_map_resource(dev, phys_addr, size, dir, addr);
> -
>   	return addr;
>   }
>   
> @@ -369,7 +371,7 @@ static inline void dma_unmap_resource(struct device *dev, dma_addr_t addr,
>   	const struct dma_map_ops *ops = get_dma_ops(dev);
>   
>   	BUG_ON(!valid_dma_direction(dir));
> -	if (ops && ops->unmap_resource)
> +	if (!dma_is_direct(ops) && ops->unmap_resource)
>   		ops->unmap_resource(dev, addr, size, dir, attrs);
>   	debug_dma_unmap_resource(dev, addr, size, dir);
>   }
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 355d16acee6d..8e0359b04957 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -356,6 +356,20 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
>   }
>   EXPORT_SYMBOL(dma_direct_map_sg);
>   
> +dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,
> +		size_t size, enum dma_data_direction dir, unsigned long attrs)
> +{
> +	dma_addr_t dma_addr = phys_to_dma(dev, paddr);
> +
> +	if (unlikely(!dma_direct_possible(dev, dma_addr, size))) {
> +		report_addr(dev, dma_addr, size);
> +		return DMA_MAPPING_ERROR;
> +	}
> +
> +	return dma_addr;
> +}
> +EXPORT_SYMBOL(dma_direct_map_resource);
> +
>   /*
>    * 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
> 

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH 2/3] dma-mapping: don't BUG when calling dma_map_resource on RAM
  2019-01-11 18:17   ` [PATCH 2/3] dma-mapping: don't BUG when calling dma_map_resource on RAM Christoph Hellwig
@ 2019-01-14 14:16     ` Robin Murphy
  0 siblings, 0 replies; 16+ messages in thread
From: Robin Murphy @ 2019-01-14 14:16 UTC (permalink / raw)
  To: Christoph Hellwig, Pawel Osciak, Marek Szyprowski, Kyungmin Park,
	Niklas Söderlund
  Cc: Russell King, linux-kernel, iommu, Mauro Carvalho Chehab,
	linuxppc-dev, linux-arm-kernel, linux-media

On 11/01/2019 18:17, Christoph Hellwig wrote:
> Use WARN_ON_ONCE to print a stack trace and return a proper error
> code instead.

I was racking my brain to remember the reasoning behind BUG_ON() being 
the only viable way to prevent errors getting through unhandled, but of 
course that was before we had a standardised DMA_MAPPING_ERROR that 
would work across all implementations.

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   include/linux/dma-mapping.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index d3087829a6df..91add0751aa5 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -353,7 +353,8 @@ static inline dma_addr_t dma_map_resource(struct device *dev,
>   	BUG_ON(!valid_dma_direction(dir));
>   
>   	/* Don't allow RAM to be mapped */

Ugh, I'm pretty sure that that "pfn_valid means RAM" misunderstanding 
originally came from me - it might be nice to have a less-misleading 
comment here, but off-hand I can't think of a succinct way to say "only 
for 'DMA' access to MMIO registers/SRAMs/etc. and not for anything the 
kernel knows as actual system/device memory" to better explain the WARN...

Either way, though,

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> -	BUG_ON(pfn_valid(PHYS_PFN(phys_addr)));
> +	if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr))))
> +		return DMA_MAPPING_ERROR;
>   
>   	if (dma_is_direct(ops))
>   		addr = dma_direct_map_resource(dev, phys_addr, size, dir, attrs);
> 

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH 1/3] dma-mapping: remove the default map_resource implementation
  2019-01-14 13:12     ` Robin Murphy
@ 2019-01-14 17:08       ` Christoph Hellwig
  0 siblings, 0 replies; 16+ messages in thread
From: Christoph Hellwig @ 2019-01-14 17:08 UTC (permalink / raw)
  To: Robin Murphy
  Cc: Niklas Söderlund, linux-media, Pawel Osciak, Russell King,
	iommu, linux-kernel, Kyungmin Park, Mauro Carvalho Chehab,
	linuxppc-dev, Christoph Hellwig, linux-arm-kernel,
	Marek Szyprowski

On Mon, Jan 14, 2019 at 01:12:33PM +0000, Robin Murphy wrote:
> Ignoring the offset was kind of intentional there, because at the time I 
> was primarily thinking about it in terms of the Keystone 2 platform where 
> the peripherals are all in the same place (0-2GB) in both the bus and CPU 
> physical address maps, and only the view of RAM differs between the two 
> (2-4GB vs. 32-34GB). However, on something like BCM283x, the peripherals 
> region is also offset from its bus address in the CPU view, but at a 
> *different* offset relative to that of RAM.

I was more thinking of the PCIe P2P case, where we need to apply a
consistent offset to translate between the CPU and the bus view.

But this isn't really used for PCIe P2P, so I guess keeping the original
sematics might be a better idea.  That being said the videobuf code seems
to rely on these offsets, so we might be between a rock and a hard place.

> Fortunately, I'm not aware of any platform which has a DMA engine behind an 
> IOMMU (and thus *needs* to use dma_map_resource() to avoid said IOMMU 
> blocking the slave device register reads/writes) and also has any nonzero 
> offsets, and AFAIK the IOMMU-less platforms above aren't using 
> dma_map_resource() at all, so this change shouldn't actually break 
> anything, but I guess we have a bit of a problem making it truly generic 
> and robust :(

Note that we don't actually use the code in this patch for ARM/ARM64
platforms with IOMMUs, as both the ARM and the ARM64 iommu code have
their own implementations of ->map_resource that actually program
the iommu (which at least for the PCIe P2P case would be wrong).

> Is this perhaps another shove in the direction of overhauling 
> dma_pfn_offset into an arbitrary "DMA ranges" lookup table?

It is long overdue anyway.

>>   		addr = ops->map_resource(dev, phys_addr, size, dir, attrs);
>
> Might it be reasonable to do:
>
> 	if (!dma_is_direct(ops) && ops->map_resource)
> 		addr = ops->map_resource(...);
> 	else
> 		addr = dma_direct_map_resource(...);
>
> and avoid having to explicitly wire up the dma_direct callback elsewhere?

No, I absolutely _want_ the callback explicitly wired up.  That is the
only way to ensure we actually intentionally support it and don't just
get a default that often won't work.  Same issue for ->mmap and
->get_sgtable.

^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource
  2019-01-14 12:42     ` Marek Szyprowski
@ 2019-01-17 17:21       ` Christoph Hellwig
  2019-01-18  9:41         ` Marek Szyprowski
  0 siblings, 1 reply; 16+ messages in thread
From: Christoph Hellwig @ 2019-01-17 17:21 UTC (permalink / raw)
  To: Marek Szyprowski
  Cc: Niklas Söderlund, Pawel Osciak, Russell King, iommu,
	linux-kernel, Kyungmin Park, Mauro Carvalho Chehab, linuxppc-dev,
	Christoph Hellwig, linux-arm-kernel, linux-media

On Mon, Jan 14, 2019 at 01:42:26PM +0100, Marek Szyprowski wrote:
> Hi Christoph,
> 
> On 2019-01-11 19:17, Christoph Hellwig wrote:
> > vb2_dc_get_userptr pokes into arm direct mapping details to get the
> > resemblance of a dma address for a a physical address that does is
> > not backed by a page struct.  Not only is this not portable to other
> > architectures with dma direct mapping offsets, but also not to uses
> > of IOMMUs of any kind.  Switch to the proper dma_map_resource /
> > dma_unmap_resource interface instead.
> >
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> There are checks for IOMMU presence in other places in vb2-dma-contig,
> so it was used only when no IOMMU is available, but I agree that the
> hacky code should be replaced by a generic code if possible.
> 
> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> 
> V4L2 pipeline works fine on older Exynos-based boards with CMA and IOMMU
> disabled.

Do you know if these rely on the offsets?  E.g. would they still work
with the patch below applied on top.  That would keep the map_resource
semantics as-is as solve the issue pointed out by Robin for now.

If not I can only think of a flag to bypass the offseting for now, but
that would be pretty ugly.  Or go for the long-term solution of
discovering the relationship between the two devices, as done by the
PCIe P2P code..

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 8e0359b04957..25bd19974223 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -359,7 +359,7 @@ EXPORT_SYMBOL(dma_direct_map_sg);
 dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,
 		size_t size, enum dma_data_direction dir, unsigned long attrs)
 {
-	dma_addr_t dma_addr = phys_to_dma(dev, paddr);
+	dma_addr_t dma_addr = paddr;
 
 	if (unlikely(!dma_direct_possible(dev, dma_addr, size))) {
 		report_addr(dev, dma_addr, size);


^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource
  2019-01-17 17:21       ` Christoph Hellwig
@ 2019-01-18  9:41         ` Marek Szyprowski
  2019-01-31 15:31           ` Christoph Hellwig
  0 siblings, 1 reply; 16+ messages in thread
From: Marek Szyprowski @ 2019-01-18  9:41 UTC (permalink / raw)
  To: Christoph Hellwig
  Cc: Niklas Söderlund, Pawel Osciak, linux-kernel, Kyungmin Park,
	Russell King, iommu, Mauro Carvalho Chehab, linuxppc-dev,
	linux-arm-kernel, linux-media

Hi Christoph,

On 2019-01-17 18:21, Christoph Hellwig wrote:
> On Mon, Jan 14, 2019 at 01:42:26PM +0100, Marek Szyprowski wrote:
>> On 2019-01-11 19:17, Christoph Hellwig wrote:
>>> vb2_dc_get_userptr pokes into arm direct mapping details to get the
>>> resemblance of a dma address for a a physical address that does is
>>> not backed by a page struct.  Not only is this not portable to other
>>> architectures with dma direct mapping offsets, but also not to uses
>>> of IOMMUs of any kind.  Switch to the proper dma_map_resource /
>>> dma_unmap_resource interface instead.
>>>
>>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>> There are checks for IOMMU presence in other places in vb2-dma-contig,
>> so it was used only when no IOMMU is available, but I agree that the
>> hacky code should be replaced by a generic code if possible.
>>
>> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
>>
>> V4L2 pipeline works fine on older Exynos-based boards with CMA and IOMMU
>> disabled.
> Do you know if these rely on the offsets?  E.g. would they still work
> with the patch below applied on top.  That would keep the map_resource
> semantics as-is as solve the issue pointed out by Robin for now.

AFAIK that code was only used for sharing buffers between hardware
modules that are a part of the same SoC, usually implemented as platform
devices. AFAIR this never worked for devices on different buses. So far
I wasn't aware on ANY which would require an offset for the DMA access.

The first version of videobuf2-dc code even incorrectly used paddr
instead of dma_addr as a buffer 'address' returned to the client
drivers, because in case of those SoC this was exactly the same (see
commits 472af2b05bdefcaee7e754e22cbf131110017ad6 and
ba7fcb0c954921534707f08ebc4d8beeb2eb17e7).

> If not I can only think of a flag to bypass the offseting for now, but
> that would be pretty ugly.  Or go for the long-term solution of
> discovering the relationship between the two devices, as done by the
> PCIe P2P code..
>
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 8e0359b04957..25bd19974223 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -359,7 +359,7 @@ EXPORT_SYMBOL(dma_direct_map_sg);
>  dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,
>  		size_t size, enum dma_data_direction dir, unsigned long attrs)
>  {
> -	dma_addr_t dma_addr = phys_to_dma(dev, paddr);
> +	dma_addr_t dma_addr = paddr;
>  
>  	if (unlikely(!dma_direct_possible(dev, dma_addr, size))) {
>  		report_addr(dev, dma_addr, size);
>
>
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland


^ permalink raw reply	[flat|nested] 16+ messages in thread

* Re: [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource
  2019-01-18  9:41         ` Marek Szyprowski
@ 2019-01-31 15:31           ` Christoph Hellwig
  0 siblings, 0 replies; 16+ messages in thread
From: Christoph Hellwig @ 2019-01-31 15:31 UTC (permalink / raw)
  To: Marek Szyprowski
  Cc: Niklas Söderlund, Pawel Osciak, Russell King, iommu,
	linux-kernel, Kyungmin Park, Mauro Carvalho Chehab, linuxppc-dev,
	Christoph Hellwig, linux-arm-kernel, linux-media

Hi Marek,

can chance you could retest the v2 version?

^ permalink raw reply	[flat|nested] 16+ messages in thread

end of thread, back to index

Thread overview: 16+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
     [not found] <CGME20190111181841epcas3p2d7c0bf8f5c11a9863e22ec1b12da6e1b@epcas3p2.samsung.com>
2019-01-11 18:17 ` fix a layering violation in videobuf2 and improve dma_map_resource Christoph Hellwig
2019-01-11 18:17   ` [PATCH 1/3] dma-mapping: remove the default map_resource implementation Christoph Hellwig
2019-01-14 13:12     ` Robin Murphy
2019-01-14 17:08       ` Christoph Hellwig
2019-01-11 18:17   ` [PATCH 2/3] dma-mapping: don't BUG when calling dma_map_resource on RAM Christoph Hellwig
2019-01-14 14:16     ` Robin Murphy
2019-01-11 18:17   ` [PATCH 3/3] videobuf2: replace a layering violation with dma_map_resource Christoph Hellwig
2019-01-11 19:54     ` Mauro Carvalho Chehab
2019-01-14 10:31       ` Christoph Hellwig
2019-01-14 11:04         ` Mauro Carvalho Chehab
2019-01-14 11:12           ` Christoph Hellwig
2019-01-14 12:42     ` Marek Szyprowski
2019-01-17 17:21       ` Christoph Hellwig
2019-01-18  9:41         ` Marek Szyprowski
2019-01-31 15:31           ` Christoph Hellwig
2019-01-14 11:43   ` fix a layering violation in videobuf2 and improve dma_map_resource Marek Szyprowski

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