[PATCH v2 0/2] XEN SWIOTLB for ARM dma operations extension

[PATCH v2 0/2] XEN SWIOTLB for ARM dma operations extension

[Andrii Anisov]

From: Andrii Anisov <andrii_anisov@epam.com>

Some drivers need additional dma ops to be provided by xen swiotlb. Because
common operations implementation came from x86 world and does not suite ARM
needs we have to provide needed XEN SWIOTLB for ARM callbacks.

dma_mmap patch is a port of an antique and lost patch discussed here:
http://marc.info/?l=xen-devel&m=139695901430667&w=4

Changes in V2:
 - patches are rebased and checked for compilation for x86, arm, arm64 with
   the current LK master HEAD 83346fbc07d267de777e2597552f785174ad0373

Andrii Anisov (1):
  swiotlb-xen: implement xen_swiotlb_get_sgtable callback

Stefano Stabellini (1):
  swiotlb-xen: implement xen_swiotlb_dma_mmap callback

 arch/arm/xen/mm.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

-- 
2.7.4


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[PATCH v2 1/2] swiotlb-xen: implement xen_swiotlb_dma_mmap callback

[Andrii Anisov]

From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

This function creates userspace mapping for the DMA-coherent memory.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn@globallogic.com>
Signed-off-by: Andrii Anisov <andrii_anisov@epam.com>
---
 arch/arm/xen/mm.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index bd62d94..ff812a2 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -163,6 +163,19 @@ bool xen_arch_need_swiotlb(struct device *dev,
 		!is_device_dma_coherent(dev));
 }
 
+/*
+ * Create userspace mapping for the DMA-coherent memory.
+ */
+static int xen_swiotlb_dma_mmap(struct device *dev, struct vm_area_struct *vma,
+			 void *cpu_addr, dma_addr_t dma_addr, size_t size,
+			 unsigned long attrs)
+{
+	if (__generic_dma_ops(dev)->mmap)
+		return __generic_dma_ops(dev)->mmap(dev, vma, cpu_addr, dma_addr, size, attrs);
+
+	return dma_common_mmap(dev, vma, cpu_addr, dma_addr, size);
+}
+
 int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
 				 unsigned int address_bits,
 				 dma_addr_t *dma_handle)
@@ -198,6 +211,7 @@ static struct dma_map_ops xen_swiotlb_dma_ops = {
 	.unmap_page = xen_swiotlb_unmap_page,
 	.dma_supported = xen_swiotlb_dma_supported,
 	.set_dma_mask = xen_swiotlb_set_dma_mask,
+	.mmap = xen_swiotlb_dma_mmap,
 };
 
 int __init xen_mm_init(void)
-- 
2.7.4


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[PATCH v2 2/2] swiotlb-xen: implement xen_swiotlb_get_sgtable callback

[Andrii Anisov]

From: Andrii Anisov <andrii_anisov@epam.com>

Signed-off-by: Andrii Anisov <andrii_anisov@epam.com>
---
 arch/arm/xen/mm.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index ff812a2..dc83a35 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -176,6 +176,16 @@ static int xen_swiotlb_dma_mmap(struct device *dev, struct vm_area_struct *vma,
 	return dma_common_mmap(dev, vma, cpu_addr, dma_addr, size);
 }
 
+static int xen_swiotlb_get_sgtable(struct device *dev, struct sg_table *sgt,
+				 void *cpu_addr, dma_addr_t handle, size_t size,
+				 unsigned long attrs)
+{
+	if (__generic_dma_ops(dev)->get_sgtable)
+		return __generic_dma_ops(dev)->get_sgtable(dev, sgt, cpu_addr, handle,
+								 size, attrs);
+	return dma_common_get_sgtable(dev, sgt, cpu_addr, handle, size);
+}
+
 int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
 				 unsigned int address_bits,
 				 dma_addr_t *dma_handle)
@@ -212,6 +222,7 @@ static struct dma_map_ops xen_swiotlb_dma_ops = {
 	.dma_supported = xen_swiotlb_dma_supported,
 	.set_dma_mask = xen_swiotlb_set_dma_mask,
 	.mmap = xen_swiotlb_dma_mmap,
+	.get_sgtable = xen_swiotlb_get_sgtable,
 };
 
 int __init xen_mm_init(void)
-- 
2.7.4


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Re: [PATCH v2 1/2] swiotlb-xen: implement xen_swiotlb_dma_mmap callback

[Stefano Stabellini]

On Mon, 16 Jan 2017, Andrii Anisov wrote:
> From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> 
> This function creates userspace mapping for the DMA-coherent memory.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn@globallogic.com>
> Signed-off-by: Andrii Anisov <andrii_anisov@epam.com>
> ---
>  arch/arm/xen/mm.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
> index bd62d94..ff812a2 100644
> --- a/arch/arm/xen/mm.c
> +++ b/arch/arm/xen/mm.c
> @@ -163,6 +163,19 @@ bool xen_arch_need_swiotlb(struct device *dev,
>  		!is_device_dma_coherent(dev));
>  }
>  
> +/*
> + * Create userspace mapping for the DMA-coherent memory.
> + */
> +static int xen_swiotlb_dma_mmap(struct device *dev, struct vm_area_struct *vma,
> +			 void *cpu_addr, dma_addr_t dma_addr, size_t size,
> +			 unsigned long attrs)
> +{
> +	if (__generic_dma_ops(dev)->mmap)
> +		return __generic_dma_ops(dev)->mmap(dev, vma, cpu_addr, dma_addr, size, attrs);
> +
> +	return dma_common_mmap(dev, vma, cpu_addr, dma_addr, size);
> +}
> +
>  int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
>  				 unsigned int address_bits,
>  				 dma_addr_t *dma_handle)
> @@ -198,6 +211,7 @@ static struct dma_map_ops xen_swiotlb_dma_ops = {
>  	.unmap_page = xen_swiotlb_unmap_page,
>  	.dma_supported = xen_swiotlb_dma_supported,
>  	.set_dma_mask = xen_swiotlb_set_dma_mask,
> +	.mmap = xen_swiotlb_dma_mmap,
>  };
>  
>  int __init xen_mm_init(void)

The patch should work fine and looks OK. It is better written like this,
compared to the previous versions that reimplemented dma_common_mmap. I
like the fact that we are reusing the arm specific generic mmap
functions via __generic_dma_ops.

For consistency, I would prefer to have xen_swiotlb_dma_mmap in
drivers/xen/swiotlb-xen.c, even if it needs to be #ifdef'ed CONFIG_ARM
(at least the __generic_dma_ops calls need to be #ifdef'ed).

Konrad, what do you think?

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Re: [PATCH v2 1/2] swiotlb-xen: implement xen_swiotlb_dma_mmap callback

[Stefano Stabellini]

On Mon, 16 Jan 2017, Stefano Stabellini wrote:
> On Mon, 16 Jan 2017, Andrii Anisov wrote:
> > From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > 
> > This function creates userspace mapping for the DMA-coherent memory.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn@globallogic.com>
> > Signed-off-by: Andrii Anisov <andrii_anisov@epam.com>
> > ---
> >  arch/arm/xen/mm.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
> > index bd62d94..ff812a2 100644
> > --- a/arch/arm/xen/mm.c
> > +++ b/arch/arm/xen/mm.c
> > @@ -163,6 +163,19 @@ bool xen_arch_need_swiotlb(struct device *dev,
> >  		!is_device_dma_coherent(dev));
> >  }
> >  
> > +/*
> > + * Create userspace mapping for the DMA-coherent memory.
> > + */
> > +static int xen_swiotlb_dma_mmap(struct device *dev, struct vm_area_struct *vma,
> > +			 void *cpu_addr, dma_addr_t dma_addr, size_t size,
> > +			 unsigned long attrs)
> > +{

Only one suggestion more. For this to work correctly, we are assuming
that no foreging pages are involved here, which is a very reasonable
assumption given that mmap should be called on memory returned by
dma_alloc_coherent.  Please add an in-code comment here so that we'll
remember.


> > +	if (__generic_dma_ops(dev)->mmap)
> > +		return __generic_dma_ops(dev)->mmap(dev, vma, cpu_addr, dma_addr, size, attrs);
> > +
> > +	return dma_common_mmap(dev, vma, cpu_addr, dma_addr, size);
> > +}
> > +
> >  int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
> >  				 unsigned int address_bits,
> >  				 dma_addr_t *dma_handle)
> > @@ -198,6 +211,7 @@ static struct dma_map_ops xen_swiotlb_dma_ops = {
> >  	.unmap_page = xen_swiotlb_unmap_page,
> >  	.dma_supported = xen_swiotlb_dma_supported,
> >  	.set_dma_mask = xen_swiotlb_set_dma_mask,
> > +	.mmap = xen_swiotlb_dma_mmap,
> >  };
> >  
> >  int __init xen_mm_init(void)
> 
> The patch should work fine and looks OK. It is better written like this,
> compared to the previous versions that reimplemented dma_common_mmap. I
> like the fact that we are reusing the arm specific generic mmap
> functions via __generic_dma_ops.
> 
> For consistency, I would prefer to have xen_swiotlb_dma_mmap in
> drivers/xen/swiotlb-xen.c, even if it needs to be #ifdef'ed CONFIG_ARM
> (at least the __generic_dma_ops calls need to be #ifdef'ed).
> 
> Konrad, what do you think?
> 

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Re: [PATCH v2 1/2] swiotlb-xen: implement xen_swiotlb_dma_mmap callback

[Andrii Anisov]

[-- Attachment #1.1: Type: text/plain, Size: 4526 bytes --]


Dear Stefano,


> Only one suggestion more. For this to work correctly, we are assuming
> that no foreging pages are involved here, which is a very reasonable
> assumption given that mmap should be called on memory returned by
> dma_alloc_coherent.

I also kept in mind this problem, that's why the first version was RFC.

> Please add an in-code comment here so that we'll remember.

Do you think comment would be enough so far?
Maybe fallback to common ops would be better in order to keep current (even broken) functionality for now? Or BUG_ON as you suggested for get_sgtable callback?


ANDRII ANISOV

Lead Systems Engineer



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________________________________
From: Stefano Stabellini <sstabellini@kernel.org>
Sent: Tuesday, January 17, 2017 12:56:12 AM
To: Stefano Stabellini
Cc: Andrii Anisov; xen-devel@lists.xenproject.org; Andrii Anisov; julien.grall@arm.com; konrad.wilk@oracle.com; Stefano Stabellini; Oleksandr Dmytryshyn
Subject: Re: [PATCH v2 1/2] swiotlb-xen: implement xen_swiotlb_dma_mmap callback

On Mon, 16 Jan 2017, Stefano Stabellini wrote:
> On Mon, 16 Jan 2017, Andrii Anisov wrote:
> > From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> >
> > This function creates userspace mapping for the DMA-coherent memory.
> >
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > Signed-off-by: Oleksandr Dmytryshyn <oleksandr.dmytryshyn@globallogic.com>
> > Signed-off-by: Andrii Anisov <andrii_anisov@epam.com>
> > ---
> >  arch/arm/xen/mm.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> >
> > diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
> > index bd62d94..ff812a2 100644
> > --- a/arch/arm/xen/mm.c
> > +++ b/arch/arm/xen/mm.c
> > @@ -163,6 +163,19 @@ bool xen_arch_need_swiotlb(struct device *dev,
> >              !is_device_dma_coherent(dev));
> >  }
> >
> > +/*
> > + * Create userspace mapping for the DMA-coherent memory.
> > + */
> > +static int xen_swiotlb_dma_mmap(struct device *dev, struct vm_area_struct *vma,
> > +                    void *cpu_addr, dma_addr_t dma_addr, size_t size,
> > +                    unsigned long attrs)
> > +{

Only one suggestion more. For this to work correctly, we are assuming
that no foreging pages are involved here, which is a very reasonable
assumption given that mmap should be called on memory returned by
dma_alloc_coherent.  Please add an in-code comment here so that we'll
remember.


> > +   if (__generic_dma_ops(dev)->mmap)
> > +           return __generic_dma_ops(dev)->mmap(dev, vma, cpu_addr, dma_addr, size, attrs);
> > +
> > +   return dma_common_mmap(dev, vma, cpu_addr, dma_addr, size);
> > +}
> > +
> >  int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
> >                               unsigned int address_bits,
> >                               dma_addr_t *dma_handle)
> > @@ -198,6 +211,7 @@ static struct dma_map_ops xen_swiotlb_dma_ops = {
> >      .unmap_page = xen_swiotlb_unmap_page,
> >      .dma_supported = xen_swiotlb_dma_supported,
> >      .set_dma_mask = xen_swiotlb_set_dma_mask,
> > +   .mmap = xen_swiotlb_dma_mmap,
> >  };
> >
> >  int __init xen_mm_init(void)
>
> The patch should work fine and looks OK. It is better written like this,
> compared to the previous versions that reimplemented dma_common_mmap. I
> like the fact that we are reusing the arm specific generic mmap
> functions via __generic_dma_ops.
>
> For consistency, I would prefer to have xen_swiotlb_dma_mmap in
> drivers/xen/swiotlb-xen.c, even if it needs to be #ifdef'ed CONFIG_ARM
> (at least the __generic_dma_ops calls need to be #ifdef'ed).
>
> Konrad, what do you think?
>

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Re: [PATCH v2 1/2] swiotlb-xen: implement xen_swiotlb_dma_mmap callback

[Stefano Stabellini]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1956 bytes --]

On Wed, 18 Jan 2017, Andrii Anisov wrote:
> Dear Stefano,
> 
> 
> > Only one suggestion more. For this to work correctly, we are assuming
> > that no foreging pages are involved here, which is a very reasonable
> > assumption given that mmap should be called on memory returned by
> > dma_alloc_coherent.
> 
> I also kept in mind this problem, that's why the first version was RFC.
> 
> > Please add an in-code comment here so that we'll remember.
> 
> Do you think comment would be enough so far?

A comment is enough in the case of xen_swiotlb_dma_mmap, because we are
sure that the function can only be called with local pages. See the
comment above dma_mmap_attrs:

 * Map a coherent DMA buffer previously allocated by dma_alloc_attrs
 * into user space.  The coherent DMA buffer must not be freed by the
 * driver until the user space mapping has been released.

If the page must comes from dma_alloc_coherent, then we are safe.


I wasn't sure about dma_get_sgtable_attrs, because there is no in-tree
description, but looking at git log:

  commit d2b7428eb0caa7c66e34b6ac869a43915b294123
  Author: Marek Szyprowski <m.szyprowski@samsung.com>
  Date:   Wed Jun 13 10:05:52 2012 +0200
  
      common: dma-mapping: introduce dma_get_sgtable() function
      
      This patch adds dma_get_sgtable() function which is required to let
      drivers to share the buffers allocated by DMA-mapping subsystem. Right

It looks like dma_get_sgtable is also supposed to be called on buffers
returned by dma_alloc_coherent. We should be safe in both cases.


> Maybe fallback to common ops would be better in order to keep current (even broken) functionality for now? Or
> BUG_ON as you suggested for get_sgtable callback?

BUG_ON is good because it is an obvious failure for a case we don't know
how to handle. If it actually works as expected, we could add it to
both functions anyway, surrounded by #ifdef DEBUG_DRIVER not to slow
down the common case.

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[PATCH v2 0/2] XEN SWIOTLB for ARM dma operations extension

[Andrii Anisov]

From: Andrii Anisov <andrii_anisov@epam.com>

Some drivers need additional dma ops to be provided by xen swiotlb. Because
common operations implementation came from x86 world and does not suite ARM
needs we have to provide needed XEN SWIOTLB for ARM callbacks.

dma_mmap patch is a port of an antique and lost patch discussed here:
http://marc.info/?l=xen-devel&m=139695901430667&w=4

Changes in V2:
 - patches are rebased and checked for compilation for x86, arm, arm64 with
   the current LK master HEAD 83346fbc07d267de777e2597552f785174ad0373

Andrii Anisov (1):
  swiotlb-xen: implement xen_swiotlb_get_sgtable callback

Stefano Stabellini (1):
  swiotlb-xen: implement xen_swiotlb_dma_mmap callback

 arch/arm/xen/mm.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

-- 
2.7.4


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