[PATCH 0/2] dma-parms and helpers for dma-buf

[PATCH 0/2] dma-parms and helpers for dma-buf

[Rob Clark]

From: Rob Clark <rob@ti.com>

Re-sending first patch, with a wider audience.  Apparently I didn't
spam enough inboxes the first time.

And, at Daniel Vetter's suggestion, adding some helper functions in
dma-buf to get the most restrictive parameters of all the attached
devices.

Rob Clark (2):
  device: add dma_params->max_segment_count
  dma-buf: add helpers for attacher dma-parms

 drivers/base/dma-buf.c      |   63 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/device.h      |    1 +
 include/linux/dma-buf.h     |   19 +++++++++++++
 include/linux/dma-mapping.h |   16 +++++++++++
 4 files changed, 99 insertions(+)

-- 
1.7.9.5

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[PATCH 1/2] device: add dma_params->max_segment_count

[Rob Clark]

From: Rob Clark <rob@ti.com>

For devices which have constraints about maximum number of segments
in an sglist.  For example, a device which could only deal with
contiguous buffers would set max_segment_count to 1.

The initial motivation is for devices sharing buffers via dma-buf,
to allow the buffer exporter to know the constraints of other
devices which have attached to the buffer.  The dma_mask and fields
in 'struct device_dma_parameters' tell the exporter everything else
that is needed, except whether the importer has constraints about
maximum number of segments.

Signed-off-by: Rob Clark <rob@ti.com>
---
 include/linux/device.h      |    1 +
 include/linux/dma-mapping.h |   16 ++++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/linux/device.h b/include/linux/device.h
index 161d962..3813735 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -568,6 +568,7 @@ struct device_dma_parameters {
 	 * sg limitations.
 	 */
 	unsigned int max_segment_size;
+	unsigned int max_segment_count;    /* zero for unlimited */
 	unsigned long segment_boundary_mask;
 };
 
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index dfc099e..f380f79 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -111,6 +111,22 @@ static inline unsigned int dma_set_max_seg_size(struct device *dev,
 		return -EIO;
 }
 
+static inline unsigned int dma_get_max_seg_count(struct device *dev)
+{
+	return dev->dma_parms ? dev->dma_parms->max_segment_count : 0;
+}
+
+static inline int dma_set_max_seg_count(struct device *dev,
+						unsigned int count)
+{
+	if (dev->dma_parms) {
+		dev->dma_parms->max_segment_count = count;
+		return 0;
+	} else
+		return -EIO;
+}
+
+
 static inline unsigned long dma_get_seg_boundary(struct device *dev)
 {
 	return dev->dma_parms ?
-- 
1.7.9.5

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RE: [PATCH 1/2] device: add dma_params->max_segment_count

[Marek Szyprowski]

Hello,

On Thursday, July 19, 2012 6:24 PM Rob Clark wrote:

> From: Rob Clark <rob@ti.com>
> 
> For devices which have constraints about maximum number of segments
> in an sglist.  For example, a device which could only deal with
> contiguous buffers would set max_segment_count to 1.
> 
> The initial motivation is for devices sharing buffers via dma-buf,
> to allow the buffer exporter to know the constraints of other
> devices which have attached to the buffer.  The dma_mask and fields
> in 'struct device_dma_parameters' tell the exporter everything else
> that is needed, except whether the importer has constraints about
> maximum number of segments.
> 
> Signed-off-by: Rob Clark <rob@ti.com>

Yea, it is a really good idea to add this to struct device_dma_parameters.
We only need to initialize it to '1' in platform startup code for all 
devices relevant to buffer sharing.

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

> ---
>  include/linux/device.h      |    1 +
>  include/linux/dma-mapping.h |   16 ++++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 161d962..3813735 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -568,6 +568,7 @@ struct device_dma_parameters {
>  	 * sg limitations.
>  	 */
>  	unsigned int max_segment_size;
> +	unsigned int max_segment_count;    /* zero for unlimited */
>  	unsigned long segment_boundary_mask;
>  };
> 
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index dfc099e..f380f79 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -111,6 +111,22 @@ static inline unsigned int dma_set_max_seg_size(struct device *dev,
>  		return -EIO;
>  }
> 
> +static inline unsigned int dma_get_max_seg_count(struct device *dev)
> +{
> +	return dev->dma_parms ? dev->dma_parms->max_segment_count : 0;
> +}
> +
> +static inline int dma_set_max_seg_count(struct device *dev,
> +						unsigned int count)
> +{
> +	if (dev->dma_parms) {
> +		dev->dma_parms->max_segment_count = count;
> +		return 0;
> +	} else
> +		return -EIO;
> +}
> +
> +
>  static inline unsigned long dma_get_seg_boundary(struct device *dev)
>  {
>  	return dev->dma_parms ?
> --
> 1.7.9.5

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center



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[PATCH 2/2] dma-buf: add helpers for attacher dma-parms

[Rob Clark]

From: Rob Clark <rob@ti.com>

Add some helpers to iterate through all attachers and get the most
restrictive segment size/count/boundary.

Signed-off-by: Rob Clark <rob@ti.com>
---
 drivers/base/dma-buf.c  |   63 +++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/dma-buf.h |   19 ++++++++++++++
 2 files changed, 82 insertions(+)

diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
index 24e88fe..757ee20 100644
--- a/drivers/base/dma-buf.c
+++ b/drivers/base/dma-buf.c
@@ -192,6 +192,69 @@ void dma_buf_put(struct dma_buf *dmabuf)
 EXPORT_SYMBOL_GPL(dma_buf_put);
 
 /**
+ * dma_buf_max_seg_size - helper for exporters to get the minimum of
+ * all attached device's max segment size
+ */
+unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf)
+{
+	struct dma_buf_attachment *attach;
+	unsigned int max = (unsigned int)-1;
+
+	if (WARN_ON(!dmabuf))
+		return 0;
+
+	mutex_lock(&dmabuf->lock);
+	list_for_each_entry(attach, &dmabuf->attachments, node)
+		max = min(max, dma_get_max_seg_size(attach->dev));
+	mutex_unlock(&dmabuf->lock);
+
+	return max;
+}
+EXPORT_SYMBOL_GPL(dma_buf_max_seg_size);
+
+/**
+ * dma_buf_max_seg_count - helper for exporters to get the minimum of
+ * all attached device's max segment count
+ */
+unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf)
+{
+	struct dma_buf_attachment *attach;
+	unsigned int max = (unsigned int)-1;
+
+	if (WARN_ON(!dmabuf))
+		return 0;
+
+	mutex_lock(&dmabuf->lock);
+	list_for_each_entry(attach, &dmabuf->attachments, node)
+		max = min(max, dma_get_max_seg_count(attach->dev));
+	mutex_unlock(&dmabuf->lock);
+
+	return max;
+}
+EXPORT_SYMBOL_GPL(dma_buf_max_seg_count);
+
+/**
+ * dma_buf_get_seg_boundary - helper for exporters to get the most
+ * restrictive segment alignment of all the attached devices
+ */
+unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf)
+{
+	struct dma_buf_attachment *attach;
+	unsigned int mask = (unsigned int)-1;
+
+	if (WARN_ON(!dmabuf))
+		return 0;
+
+	mutex_lock(&dmabuf->lock);
+	list_for_each_entry(attach, &dmabuf->attachments, node)
+		mask &= dma_get_seg_boundary(attach->dev);
+	mutex_unlock(&dmabuf->lock);
+
+	return mask;
+}
+EXPORT_SYMBOL_GPL(dma_buf_get_seg_boundary);
+
+/**
  * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
  * calls attach() of dma_buf_ops to allow device-specific attach functionality
  * @dmabuf:	[in]	buffer to attach device to.
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index eb48f38..9533b9b 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -167,6 +167,10 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags);
 struct dma_buf *dma_buf_get(int fd);
 void dma_buf_put(struct dma_buf *dmabuf);
 
+unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf);
+unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf);
+unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf);
+
 struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
 					enum dma_data_direction);
 void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
@@ -220,6 +224,21 @@ static inline void dma_buf_put(struct dma_buf *dmabuf)
 	return;
 }
 
+static inline unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf)
+{
+	return 0;
+}
+
+static inline unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf)
+{
+	return 0;
+}
+
+static inline unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf)
+{
+	return 0;
+}
+
 static inline struct sg_table *dma_buf_map_attachment(
 	struct dma_buf_attachment *attach, enum dma_data_direction write)
 {
-- 
1.7.9.5

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Re: [PATCH 2/2] dma-buf: add helpers for attacher dma-parms

[Rob Clark]

Fyi, Daniel Vetter had suggested on IRC that it would be cleaner to
have a single helper fxn that most-restrictive union of all attached
device's dma_parms.  Really this should include dma_mask and
coherent_dma_mask, I think.  But that touches a lot of other places in
the code.  If no one objects to the cleanup of moving
dma_mask/coherent_dma_mask into dma_parms, I'll do this first.

So anyways, don't consider this patch yet for inclusion, I'll make an
updated one based on dma_parms..

BR,
-R

On Thu, Jul 19, 2012 at 11:23 AM, Rob Clark <rob.clark@linaro.org> wrote:
> From: Rob Clark <rob@ti.com>
>
> Add some helpers to iterate through all attachers and get the most
> restrictive segment size/count/boundary.
>
> Signed-off-by: Rob Clark <rob@ti.com>
> ---
>  drivers/base/dma-buf.c  |   63 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/dma-buf.h |   19 ++++++++++++++
>  2 files changed, 82 insertions(+)
>
> diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
> index 24e88fe..757ee20 100644
> --- a/drivers/base/dma-buf.c
> +++ b/drivers/base/dma-buf.c
> @@ -192,6 +192,69 @@ void dma_buf_put(struct dma_buf *dmabuf)
>  EXPORT_SYMBOL_GPL(dma_buf_put);
>
>  /**
> + * dma_buf_max_seg_size - helper for exporters to get the minimum of
> + * all attached device's max segment size
> + */
> +unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf)
> +{
> +       struct dma_buf_attachment *attach;
> +       unsigned int max = (unsigned int)-1;
> +
> +       if (WARN_ON(!dmabuf))
> +               return 0;
> +
> +       mutex_lock(&dmabuf->lock);
> +       list_for_each_entry(attach, &dmabuf->attachments, node)
> +               max = min(max, dma_get_max_seg_size(attach->dev));
> +       mutex_unlock(&dmabuf->lock);
> +
> +       return max;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_max_seg_size);
> +
> +/**
> + * dma_buf_max_seg_count - helper for exporters to get the minimum of
> + * all attached device's max segment count
> + */
> +unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf)
> +{
> +       struct dma_buf_attachment *attach;
> +       unsigned int max = (unsigned int)-1;
> +
> +       if (WARN_ON(!dmabuf))
> +               return 0;
> +
> +       mutex_lock(&dmabuf->lock);
> +       list_for_each_entry(attach, &dmabuf->attachments, node)
> +               max = min(max, dma_get_max_seg_count(attach->dev));
> +       mutex_unlock(&dmabuf->lock);
> +
> +       return max;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_max_seg_count);
> +
> +/**
> + * dma_buf_get_seg_boundary - helper for exporters to get the most
> + * restrictive segment alignment of all the attached devices
> + */
> +unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf)
> +{
> +       struct dma_buf_attachment *attach;
> +       unsigned int mask = (unsigned int)-1;
> +
> +       if (WARN_ON(!dmabuf))
> +               return 0;
> +
> +       mutex_lock(&dmabuf->lock);
> +       list_for_each_entry(attach, &dmabuf->attachments, node)
> +               mask &= dma_get_seg_boundary(attach->dev);
> +       mutex_unlock(&dmabuf->lock);
> +
> +       return mask;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_get_seg_boundary);
> +
> +/**
>   * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
>   * calls attach() of dma_buf_ops to allow device-specific attach functionality
>   * @dmabuf:    [in]    buffer to attach device to.
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index eb48f38..9533b9b 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -167,6 +167,10 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags);
>  struct dma_buf *dma_buf_get(int fd);
>  void dma_buf_put(struct dma_buf *dmabuf);
>
> +unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf);
> +unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf);
> +unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf);
> +
>  struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
>                                         enum dma_data_direction);
>  void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
> @@ -220,6 +224,21 @@ static inline void dma_buf_put(struct dma_buf *dmabuf)
>         return;
>  }
>
> +static inline unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf)
> +{
> +       return 0;
> +}
> +
> +static inline unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf)
> +{
> +       return 0;
> +}
> +
> +static inline unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf)
> +{
> +       return 0;
> +}
> +
>  static inline struct sg_table *dma_buf_map_attachment(
>         struct dma_buf_attachment *attach, enum dma_data_direction write)
>  {
> --
> 1.7.9.5
>

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Re: [PATCH 2/2] dma-buf: add helpers for attacher dma-parms

[Semwal, Sumit]

On Fri, Jul 20, 2012 at 10:09 PM, Rob Clark <rob.clark@linaro.org> wrote:
> Fyi, Daniel Vetter had suggested on IRC that it would be cleaner to
> have a single helper fxn that most-restrictive union of all attached
> device's dma_parms.  Really this should include dma_mask and
> coherent_dma_mask, I think.  But that touches a lot of other places in
> the code.  If no one objects to the cleanup of moving
> dma_mask/coherent_dma_mask into dma_parms, I'll do this first.
>
> So anyways, don't consider this patch yet for inclusion, I'll make an
> updated one based on dma_parms..
Hi Rob,
Any news on this patch-set?
>
> BR,
> -R
BR,
~Sumit.
>
> On Thu, Jul 19, 2012 at 11:23 AM, Rob Clark <rob.clark@linaro.org> wrote:
>> From: Rob Clark <rob@ti.com>
>>
>> Add some helpers to iterate through all attachers and get the most
>> restrictive segment size/count/boundary.
>>
>> Signed-off-by: Rob Clark <rob@ti.com>
>> ---
>>  drivers/base/dma-buf.c  |   63 +++++++++++++++++++++++++++++++++++++++++++++++
>>  include/linux/dma-buf.h |   19 ++++++++++++++
>>  2 files changed, 82 insertions(+)
>>
>> diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
>> index 24e88fe..757ee20 100644
>> --- a/drivers/base/dma-buf.c
>> +++ b/drivers/base/dma-buf.c
>> @@ -192,6 +192,69 @@ void dma_buf_put(struct dma_buf *dmabuf)
>>  EXPORT_SYMBOL_GPL(dma_buf_put);
>>
>>  /**
>> + * dma_buf_max_seg_size - helper for exporters to get the minimum of
>> + * all attached device's max segment size
>> + */
>> +unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf)
>> +{
>> +       struct dma_buf_attachment *attach;
>> +       unsigned int max = (unsigned int)-1;
>> +
>> +       if (WARN_ON(!dmabuf))
>> +               return 0;
>> +
>> +       mutex_lock(&dmabuf->lock);
>> +       list_for_each_entry(attach, &dmabuf->attachments, node)
>> +               max = min(max, dma_get_max_seg_size(attach->dev));
>> +       mutex_unlock(&dmabuf->lock);
>> +
>> +       return max;
>> +}
>> +EXPORT_SYMBOL_GPL(dma_buf_max_seg_size);
>> +
>> +/**
>> + * dma_buf_max_seg_count - helper for exporters to get the minimum of
>> + * all attached device's max segment count
>> + */
>> +unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf)
>> +{
>> +       struct dma_buf_attachment *attach;
>> +       unsigned int max = (unsigned int)-1;
>> +
>> +       if (WARN_ON(!dmabuf))
>> +               return 0;
>> +
>> +       mutex_lock(&dmabuf->lock);
>> +       list_for_each_entry(attach, &dmabuf->attachments, node)
>> +               max = min(max, dma_get_max_seg_count(attach->dev));
>> +       mutex_unlock(&dmabuf->lock);
>> +
>> +       return max;
>> +}
>> +EXPORT_SYMBOL_GPL(dma_buf_max_seg_count);
>> +
>> +/**
>> + * dma_buf_get_seg_boundary - helper for exporters to get the most
>> + * restrictive segment alignment of all the attached devices
>> + */
>> +unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf)
>> +{
>> +       struct dma_buf_attachment *attach;
>> +       unsigned int mask = (unsigned int)-1;
>> +
>> +       if (WARN_ON(!dmabuf))
>> +               return 0;
>> +
>> +       mutex_lock(&dmabuf->lock);
>> +       list_for_each_entry(attach, &dmabuf->attachments, node)
>> +               mask &= dma_get_seg_boundary(attach->dev);
>> +       mutex_unlock(&dmabuf->lock);
>> +
>> +       return mask;
>> +}
>> +EXPORT_SYMBOL_GPL(dma_buf_get_seg_boundary);
>> +
>> +/**
>>   * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
>>   * calls attach() of dma_buf_ops to allow device-specific attach functionality
>>   * @dmabuf:    [in]    buffer to attach device to.
>> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
>> index eb48f38..9533b9b 100644
>> --- a/include/linux/dma-buf.h
>> +++ b/include/linux/dma-buf.h
>> @@ -167,6 +167,10 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags);
>>  struct dma_buf *dma_buf_get(int fd);
>>  void dma_buf_put(struct dma_buf *dmabuf);
>>
>> +unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf);
>> +unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf);
>> +unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf);
>> +
>>  struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
>>                                         enum dma_data_direction);
>>  void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
>> @@ -220,6 +224,21 @@ static inline void dma_buf_put(struct dma_buf *dmabuf)
>>         return;
>>  }
>>
>> +static inline unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf)
>> +{
>> +       return 0;
>> +}
>> +
>> +static inline unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf)
>> +{
>> +       return 0;
>> +}
>> +
>> +static inline unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf)
>> +{
>> +       return 0;
>> +}
>> +
>>  static inline struct sg_table *dma_buf_map_attachment(
>>         struct dma_buf_attachment *attach, enum dma_data_direction write)
>>  {
>> --
>> 1.7.9.5
>>

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Re: [PATCH 2/2] dma-buf: add helpers for attacher dma-parms

[Tomasz Stanislawski]

Hi Rob,

On 07/19/2012 06:23 PM, Rob Clark wrote:
> From: Rob Clark <rob@ti.com>
> 
> Add some helpers to iterate through all attachers and get the most
> restrictive segment size/count/boundary.
> 
> Signed-off-by: Rob Clark <rob@ti.com>
> ---
>  drivers/base/dma-buf.c  |   63 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/dma-buf.h |   19 ++++++++++++++
>  2 files changed, 82 insertions(+)
> 
> diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
> index 24e88fe..757ee20 100644
> --- a/drivers/base/dma-buf.c
> +++ b/drivers/base/dma-buf.c
> @@ -192,6 +192,69 @@ void dma_buf_put(struct dma_buf *dmabuf)
>  EXPORT_SYMBOL_GPL(dma_buf_put);
>  
>  /**
> + * dma_buf_max_seg_size - helper for exporters to get the minimum of
> + * all attached device's max segment size
> + */
> +unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf)
> +{
> +	struct dma_buf_attachment *attach;
> +	unsigned int max = (unsigned int)-1;
> +
> +	if (WARN_ON(!dmabuf))
> +		return 0;

Maybe you should change return type to 'int' and return -EINVAL here?

> +
> +	mutex_lock(&dmabuf->lock);
> +	list_for_each_entry(attach, &dmabuf->attachments, node)
> +		max = min(max, dma_get_max_seg_size(attach->dev));
> +	mutex_unlock(&dmabuf->lock);
> +
> +	return max;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_max_seg_size);
> +
> +/**
> + * dma_buf_max_seg_count - helper for exporters to get the minimum of
> + * all attached device's max segment count
> + */
> +unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf)
> +{
> +	struct dma_buf_attachment *attach;
> +	unsigned int max = (unsigned int)-1;
> +
> +	if (WARN_ON(!dmabuf))
> +		return 0;

maybe return -EINVAL here?

> +
> +	mutex_lock(&dmabuf->lock);
> +	list_for_each_entry(attach, &dmabuf->attachments, node)
> +		max = min(max, dma_get_max_seg_count(attach->dev));

I think that there is a bug here.
Assume that there are two deices on the list, one using unlimited number of
segments (value 0), the second one needs a contiguous buffer (value 1).
The result of the function is 0 = min(0, 2).

The return value 0 indicates that the unlimited number of sg segments is
accepted what is *wrong* because the correct value should be 1.

I recommend to change the semantics for unlimited number of segments
from 'value 0' to:

#define DMA_SEGMENTS_COUNT_UNLIMITED ((unsigned long)INT_MAX)

Using INT_MAX will allow using safe conversions between signed and
unsigned integers.

> +	mutex_unlock(&dmabuf->lock);
> +
> +	return max;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_max_seg_count);
> +
> +/**
> + * dma_buf_get_seg_boundary - helper for exporters to get the most
> + * restrictive segment alignment of all the attached devices
> + */
> +unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf)
> +{
> +	struct dma_buf_attachment *attach;
> +	unsigned int mask = (unsigned int)-1;
> +
> +	if (WARN_ON(!dmabuf))
> +		return 0;
> +
> +	mutex_lock(&dmabuf->lock);
> +	list_for_each_entry(attach, &dmabuf->attachments, node)
> +		mask &= dma_get_seg_boundary(attach->dev);
> +	mutex_unlock(&dmabuf->lock);
> +
> +	return mask;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_get_seg_boundary);
> +
> +/**
>   * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
>   * calls attach() of dma_buf_ops to allow device-specific attach functionality
>   * @dmabuf:	[in]	buffer to attach device to.
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index eb48f38..9533b9b 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -167,6 +167,10 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags);
>  struct dma_buf *dma_buf_get(int fd);
>  void dma_buf_put(struct dma_buf *dmabuf);
>  
> +unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf);
> +unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf);
> +unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf);

Instead of adding an army of new handlers you could provide a single helper:

int dma_buf_get_parameters(struct dma_buf *dmabuf,
	struct device_dma_parameters *params);

This function will fill *params with lowest common DMA requirements for
all devices on attachment list. Return value can be used to diagnose
errors like incorrectly initialized dma_buf pointer
(like no attachments on an attachment list).

Moreover, there will be no need to add a new handler every time
device_dma_parameters is extended.

Regards,
Tomasz Stanislawski

> +
>  struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
>  					enum dma_data_direction);
>  void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
> @@ -220,6 +224,21 @@ static inline void dma_buf_put(struct dma_buf *dmabuf)
>  	return;
>  }
>  
> +static inline unsigned int dma_buf_max_seg_size(struct dma_buf *dmabuf)
> +{
> +	return 0;
> +}
> +
> +static inline unsigned int dma_buf_max_seg_count(struct dma_buf *dmabuf)
> +{
> +	return 0;
> +}
> +
> +static inline unsigned int dma_buf_get_seg_boundary(struct dma_buf *dmabuf)
> +{
> +	return 0;
> +}
> +
>  static inline struct sg_table *dma_buf_map_attachment(
>  	struct dma_buf_attachment *attach, enum dma_data_direction write)
>  {
> 

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Re: [PATCH 2/2] dma-buf: add helpers for attacher dma-parms

[Michal Nazarewicz]

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Tomasz Stanislawski <t.stanislaws@samsung.com> writes:
> I recommend to change the semantics for unlimited number of segments
> from 'value 0' to:
>
> #define DMA_SEGMENTS_COUNT_UNLIMITED ((unsigned long)INT_MAX)
>
> Using INT_MAX will allow using safe conversions between signed and
> unsigned integers.

LONG_MAX seems cleaner regardless.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
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Re: [PATCH 2/2] dma-buf: add helpers for attacher dma-parms

[Tomasz Stanislawski]

On 08/06/2012 01:58 PM, Michal Nazarewicz wrote:
> 
> Tomasz Stanislawski <t.stanislaws@samsung.com> writes:
>> I recommend to change the semantics for unlimited number of segments
>> from 'value 0' to:
>>
>> #define DMA_SEGMENTS_COUNT_UNLIMITED ((unsigned long)INT_MAX)

Sorry. It should be:
#define DMA_SEGMENTS_COUNT_UNLIMITED ((unsigned int)INT_MAX)

>>
>> Using INT_MAX will allow using safe conversions between signed and
>> unsigned integers.
> 
> LONG_MAX seems cleaner regardless.
> 
> 
> 

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