* [RFCv2 0/2] dma-parms, constraints and helpers for dma-buf
@ 2015-01-21 4:16 Sumit Semwal
2015-01-21 4:16 ` [RFCv2 1/2] device: add dma_params->max_segment_count Sumit Semwal
2015-01-21 4:16 ` [RFCv2 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms Sumit Semwal
0 siblings, 2 replies; 7+ messages in thread
From: Sumit Semwal @ 2015-01-21 4:16 UTC (permalink / raw)
To: linux-kernel, linux-media, dri-devel, linaro-mm-sig,
linux-arm-kernel, linux-mm
Cc: linaro-kernel, robdclark, daniel, m.szyprowski, t.stanislaws,
Sumit Semwal
Hello Everyone,
Based on review comments received, I've split my earlier patchset on
'dma-buf constraints-enabled allocation' [1] into 2 sets:
- first one is this one, to use dma_parms and related parameters from
struct device to share constraints, and then to use these constraints in
dma-buf to help find the least common constraint set that could then be
used by exporters to decide on allocation.
This is a partial re-write of what Rob Clark proposed some while ago [2];
I've tried to take care of review comments on his patchset, but any errors
and omissions are, ofcourse, mine.
- Second part, one which I'm working on, and will post soon, aims at adding
allocator-helpers in dma-buf framework which could use this constraint
information to help choose the right allocator from a list.
While I work on the second part, I thought of sending the RFC for this one,
to get feedback on whether this mechanism seems ok to everyone.
[1] https://lkml.org/lkml/2014/10/10/340
[2] https://lkml.org/lkml/2012/7/19/285
Rob Clark (1):
device: add dma_params->max_segment_count
Sumit Semwal (1):
dma-buf: add helpers for sharing attacher constraints with dma-parms
drivers/dma-buf/dma-buf.c | 134 +++++++++++++++++++++++++++++++++++++++++++-
include/linux/device.h | 1 +
include/linux/dma-buf.h | 22 ++++++++
include/linux/dma-mapping.h | 19 +++++++
4 files changed, 175 insertions(+), 1 deletion(-)
--
1.9.1
^ permalink raw reply [flat|nested] 7+ messages in thread
* [RFCv2 1/2] device: add dma_params->max_segment_count
2015-01-21 4:16 [RFCv2 0/2] dma-parms, constraints and helpers for dma-buf Sumit Semwal
@ 2015-01-21 4:16 ` Sumit Semwal
2015-01-21 18:56 ` Robin Murphy
2015-01-21 4:16 ` [RFCv2 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms Sumit Semwal
1 sibling, 1 reply; 7+ messages in thread
From: Sumit Semwal @ 2015-01-21 4:16 UTC (permalink / raw)
To: linux-kernel, linux-media, dri-devel, linaro-mm-sig,
linux-arm-kernel, linux-mm
Cc: linaro-kernel, robdclark, daniel, m.szyprowski, t.stanislaws,
Sumit Semwal
From: Rob Clark <robdclark@gmail.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 <robdclark@gmail.com>
[sumits: Minor updates wrt comments on the first version]
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
---
include/linux/device.h | 1 +
include/linux/dma-mapping.h | 19 +++++++++++++++++++
2 files changed, 20 insertions(+)
diff --git a/include/linux/device.h b/include/linux/device.h
index fb50673..a32f9b6 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -647,6 +647,7 @@ struct device_dma_parameters {
* sg limitations.
*/
unsigned int max_segment_size;
+ unsigned int max_segment_count; /* INT_MAX for unlimited */
unsigned long segment_boundary_mask;
};
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index c3007cb..38e2835 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -154,6 +154,25 @@ static inline unsigned int dma_set_max_seg_size(struct device *dev,
return -EIO;
}
+#define DMA_SEGMENTS_MAX_SEG_COUNT ((unsigned int) INT_MAX)
+
+static inline unsigned int dma_get_max_seg_count(struct device *dev)
+{
+ return dev->dma_parms ?
+ dev->dma_parms->max_segment_count :
+ DMA_SEGMENTS_MAX_SEG_COUNT;
+}
+
+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 ?
--
1.9.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [RFCv2 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms
2015-01-21 4:16 [RFCv2 0/2] dma-parms, constraints and helpers for dma-buf Sumit Semwal
2015-01-21 4:16 ` [RFCv2 1/2] device: add dma_params->max_segment_count Sumit Semwal
@ 2015-01-21 4:16 ` Sumit Semwal
2015-01-21 17:31 ` Russell King - ARM Linux
1 sibling, 1 reply; 7+ messages in thread
From: Sumit Semwal @ 2015-01-21 4:16 UTC (permalink / raw)
To: linux-kernel, linux-media, dri-devel, linaro-mm-sig,
linux-arm-kernel, linux-mm
Cc: linaro-kernel, robdclark, daniel, m.szyprowski, t.stanislaws,
Sumit Semwal
Add some helpers to share the constraints of devices while attaching
to the dmabuf buffer.
At each attach, the constraints are calculated based on the following:
- dma_mask, coherent_dma_mask from struct device,
- max_segment_size, max_segment_count, segment_boundary_mask from
device_dma_parameters.
In case the attaching device's constraints don't match up, attach() fails.
At detach, the constraints are recalculated based on the remaining
attached devices.
Two helpers are added:
- dma_buf_get_constraints - which gives the current constraints as calculated
during each attach on the buffer till the time,
- dma_buf_recalc_constraints - which recalculates the constraints for all
currently attached devices for the 'paranoid' ones amongst us.
The idea of this patch is largely taken from Rob Clark's RFC at
https://lkml.org/lkml/2012/7/19/285, and the comments received on it.
Cc: Rob Clark <robdclark@gmail.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
---
drivers/dma-buf/dma-buf.c | 132 +++++++++++++++++++++++++++++++++++++++++++++-
include/linux/dma-buf.h | 22 ++++++++
2 files changed, 153 insertions(+), 1 deletion(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 5be225c..3781f43 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -264,6 +264,77 @@ static inline int is_dma_buf_file(struct file *file)
return file->f_op == &dma_buf_fops;
}
+static inline void init_constraints(struct dma_buf_constraints *cons)
+{
+ cons->coherent_dma_mask = (u64)-1;
+ cons->dma_mask = (u64)-1;
+ cons->dma_parms.max_segment_count = (unsigned int)-1;
+ cons->dma_parms.max_segment_size = (unsigned int)-1;
+ cons->dma_parms.segment_boundary_mask = (unsigned int)-1;
+}
+
+/*
+ * calc_constraints - calculates if the new attaching device's constraints
+ * match, with the constraints of already attached devices; if yes, returns
+ * the constraints; else return ERR_PTR(-EINVAL)
+ */
+static int calc_constraints(struct device *dev,
+ struct dma_buf_constraints *calc_cons)
+{
+ struct dma_buf_constraints cons = *calc_cons;
+
+ cons.dma_mask &= dma_get_mask(dev);
+ /* TODO: Check if this is the right way for coherent_mask ? */
+ cons.coherent_dma_mask &= dev->coherent_dma_mask;
+
+ cons.dma_parms.max_segment_count =
+ min(cons.dma_parms.max_segment_count,
+ dma_get_max_seg_count(dev));
+ cons.dma_parms.max_segment_size =
+ min(cons.dma_parms.max_segment_size,
+ dma_get_max_seg_size(dev));
+ cons.dma_parms.segment_boundary_mask &=
+ dma_get_seg_boundary(dev);
+
+ if (!cons.dma_parms.max_segment_count ||
+ !cons.dma_parms.max_segment_size ||
+ !cons.dma_parms.segment_boundary_mask ||
+ !cons.dma_mask ||
+ !cons.coherent_dma_mask) {
+ pr_err("Dev: %s's constraints don't match\n", dev_name(dev));
+ return -EINVAL;
+ }
+
+ *calc_cons = cons;
+
+ return 0;
+}
+
+/*
+ * recalc_constraints - recalculates constraints for all attached devices;
+ * useful for detach() recalculation, and for dma_buf_recalc_constraints()
+ * helper.
+ * Returns recalculated constraints in recalc_cons, or error in the unlikely
+ * case when constraints of attached devices might have changed.
+ */
+static int recalc_constraints(struct dma_buf *dmabuf,
+ struct dma_buf_constraints *recalc_cons)
+{
+ struct dma_buf_constraints calc_cons;
+ struct dma_buf_attachment *attach;
+ int ret = 0;
+
+ init_constraints(&calc_cons);
+
+ list_for_each_entry(attach, &dmabuf->attachments, node) {
+ ret = calc_constraints(attach->dev, &calc_cons);
+ if (ret)
+ return ret;
+ }
+ *recalc_cons = calc_cons;
+ return 0;
+}
+
/**
* dma_buf_export_named - Creates a new dma_buf, and associates an anon file
* with this buffer, so it can be exported.
@@ -313,6 +384,9 @@ struct dma_buf *dma_buf_export_named(void *priv, const struct dma_buf_ops *ops,
dmabuf->ops = ops;
dmabuf->size = size;
dmabuf->exp_name = exp_name;
+
+ init_constraints(&dmabuf->constraints);
+
init_waitqueue_head(&dmabuf->poll);
dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll;
dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0;
@@ -422,7 +496,7 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
struct device *dev)
{
struct dma_buf_attachment *attach;
- int ret;
+ int ret = 0;
if (WARN_ON(!dmabuf || !dev))
return ERR_PTR(-EINVAL);
@@ -436,6 +510,9 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
mutex_lock(&dmabuf->lock);
+ if (calc_constraints(dev, &dmabuf->constraints))
+ goto err_constraints;
+
if (dmabuf->ops->attach) {
ret = dmabuf->ops->attach(dmabuf, dev, attach);
if (ret)
@@ -448,6 +525,7 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
err_attach:
kfree(attach);
+err_constraints:
mutex_unlock(&dmabuf->lock);
return ERR_PTR(ret);
}
@@ -470,6 +548,8 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
if (dmabuf->ops->detach)
dmabuf->ops->detach(dmabuf, attach);
+ recalc_constraints(dmabuf, &dmabuf->constraints);
+
mutex_unlock(&dmabuf->lock);
kfree(attach);
}
@@ -770,6 +850,56 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
}
EXPORT_SYMBOL_GPL(dma_buf_vunmap);
+/**
+ * dma_buf_get_constraints - get the *current* constraints of the dmabuf,
+ * as calculated during each attach(); returns error on invalid inputs
+ *
+ * @dmabuf: [in] buffer to get constraints of
+ * @constraints: [out] current constraints are returned in this
+ */
+int dma_buf_get_constraints(struct dma_buf *dmabuf,
+ struct dma_buf_constraints *constraints)
+{
+ if (WARN_ON(!dmabuf || !constraints))
+ return -EINVAL;
+
+ mutex_lock(&dmabuf->lock);
+ *constraints = dmabuf->constraints;
+ mutex_unlock(&dmabuf->lock);
+ return 0;
+}
+EXPORT_SYMBOL_GPL(dma_buf_get_constraints);
+
+/**
+ * dma_buf_recalc_constraints - *recalculate* the constraints for the buffer
+ * afresh, from the list of currently attached devices; this could be useful
+ * cross-check the current constraints, for exporters that might want to be
+ * 'paranoid' about the device constraints.
+ *
+ * returns error on invalid inputs
+ *
+ * @dmabuf: [in] buffer to get constraints of
+ * @constraints: [out] recalculated constraints are returned in this
+ */
+int dma_buf_recalc_constraints(struct dma_buf *dmabuf,
+ struct dma_buf_constraints *constraints)
+{
+ struct dma_buf_constraints calc_cons;
+ int ret = 0;
+
+ if (WARN_ON(!dmabuf || !constraints))
+ return -EINVAL;
+
+ mutex_lock(&dmabuf->lock);
+ ret = recalc_constraints(dmabuf, &calc_cons);
+ if (!ret)
+ *constraints = calc_cons;
+
+ mutex_unlock(&dmabuf->lock);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(dma_buf_recalc_constraints);
+
#ifdef CONFIG_DEBUG_FS
static int dma_buf_describe(struct seq_file *s)
{
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 694e1fe..e1f7cbe 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -34,10 +34,28 @@
#include <linux/wait.h>
struct device;
+struct device_dma_parameters;
struct dma_buf;
struct dma_buf_attachment;
/**
+ * struct dma_buf_constraints - holds constraints for the dma-buf
+ * @dma_mask: dma_mask if the device is dma'able
+ * @coherent_dma_mask: like dma_mask, but for alloc_coherent mappings
+ * @dma_parms: collated dma_parms from all devices.
+ *
+ * This structure holds the constraints of the dma_buf, dependent on the
+ * currently attached devices. Semantics for each of the members are the same
+ * as defined in device.h
+ */
+struct dma_buf_constraints {
+ u64 dma_mask;
+ u64 coherent_dma_mask;
+ struct device_dma_parameters dma_parms;
+};
+
+
+/**
* struct dma_buf_ops - operations possible on struct dma_buf
* @attach: [optional] allows different devices to 'attach' themselves to the
* given buffer. It might return -EBUSY to signal that backing storage
@@ -130,6 +148,7 @@ struct dma_buf {
void *vmap_ptr;
const char *exp_name;
struct list_head list_node;
+ struct dma_buf_constraints constraints;
void *priv;
struct reservation_object *resv;
@@ -211,4 +230,7 @@ void *dma_buf_vmap(struct dma_buf *);
void dma_buf_vunmap(struct dma_buf *, void *vaddr);
int dma_buf_debugfs_create_file(const char *name,
int (*write)(struct seq_file *));
+
+int dma_buf_get_constraints(struct dma_buf *, struct dma_buf_constraints *);
+int dma_buf_recalc_constraints(struct dma_buf *, struct dma_buf_constraints *);
#endif /* __DMA_BUF_H__ */
--
1.9.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [RFCv2 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms
2015-01-21 4:16 ` [RFCv2 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms Sumit Semwal
@ 2015-01-21 17:31 ` Russell King - ARM Linux
2015-01-27 7:04 ` Sumit Semwal
0 siblings, 1 reply; 7+ messages in thread
From: Russell King - ARM Linux @ 2015-01-21 17:31 UTC (permalink / raw)
To: Sumit Semwal
Cc: linux-kernel, linux-media, dri-devel, linaro-mm-sig,
linux-arm-kernel, linux-mm, t.stanislaws, linaro-kernel,
robdclark, daniel, m.szyprowski
On Wed, Jan 21, 2015 at 09:46:47AM +0530, Sumit Semwal wrote:
> +static int calc_constraints(struct device *dev,
> + struct dma_buf_constraints *calc_cons)
> +{
> + struct dma_buf_constraints cons = *calc_cons;
> +
> + cons.dma_mask &= dma_get_mask(dev);
I don't think this makes much sense when you consider that the DMA
infrastructure supports buses with offsets. The DMA mask is th
upper limit of the _bus_ specific address, it is not a mask per-se.
What this means is that &= is not the right operation. Moreover,
simply comparing masks which could be from devices on unrelated
buses doesn't make sense either.
However, that said, I don't have an answer for what you want to
achieve here.
--
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [RFCv2 1/2] device: add dma_params->max_segment_count
2015-01-21 4:16 ` [RFCv2 1/2] device: add dma_params->max_segment_count Sumit Semwal
@ 2015-01-21 18:56 ` Robin Murphy
2015-01-22 3:46 ` Sumit Semwal
0 siblings, 1 reply; 7+ messages in thread
From: Robin Murphy @ 2015-01-21 18:56 UTC (permalink / raw)
To: Sumit Semwal, linux-kernel, linux-media, dri-devel,
linaro-mm-sig, linux-arm-kernel, linux-mm
Cc: t.stanislaws, linaro-kernel, robdclark, daniel, m.szyprowski
Hi Sumit,
On 21/01/15 04:16, Sumit Semwal wrote:
> From: Rob Clark <robdclark@gmail.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 <robdclark@gmail.com>
> [sumits: Minor updates wrt comments on the first version]
> Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
> ---
> include/linux/device.h | 1 +
> include/linux/dma-mapping.h | 19 +++++++++++++++++++
> 2 files changed, 20 insertions(+)
>
> diff --git a/include/linux/device.h b/include/linux/device.h
> index fb50673..a32f9b6 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -647,6 +647,7 @@ struct device_dma_parameters {
> * sg limitations.
> */
> unsigned int max_segment_size;
> + unsigned int max_segment_count; /* INT_MAX for unlimited */
> unsigned long segment_boundary_mask;
> };
>
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index c3007cb..38e2835 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -154,6 +154,25 @@ static inline unsigned int dma_set_max_seg_size(struct device *dev,
> return -EIO;
> }
>
> +#define DMA_SEGMENTS_MAX_SEG_COUNT ((unsigned int) INT_MAX)
> +
> +static inline unsigned int dma_get_max_seg_count(struct device *dev)
> +{
> + return dev->dma_parms ?
> + dev->dma_parms->max_segment_count :
> + DMA_SEGMENTS_MAX_SEG_COUNT;
> +}
I know this copies the style of the existing code, but unfortunately it
also copies the subtle brokenness. Plenty of drivers seem to set up a
dma_parms struct just for max_segment_size, thus chances are you'll come
across a max_segment_count of 0 sooner or later. How badly is that going
to break things? I posted a fix recently[1] having hit this problem with
segment_boundary_mask in IOMMU code.
> +
> +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
This "else" is just as unnecessary as the other two I've taken out ;)
Robin.
[1]:http://article.gmane.org/gmane.linux.kernel.iommu/8175/
> + return -EIO;
> +}
> +
> static inline unsigned long dma_get_seg_boundary(struct device *dev)
> {
> return dev->dma_parms ?
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [RFCv2 1/2] device: add dma_params->max_segment_count
2015-01-21 18:56 ` Robin Murphy
@ 2015-01-22 3:46 ` Sumit Semwal
0 siblings, 0 replies; 7+ messages in thread
From: Sumit Semwal @ 2015-01-22 3:46 UTC (permalink / raw)
To: Robin Murphy
Cc: linux-kernel, linux-media, dri-devel, linaro-mm-sig,
linux-arm-kernel, linux-mm, t.stanislaws, linaro-kernel,
robdclark, daniel, m.szyprowski
Hi Robin!
On 22 January 2015 at 00:26, Robin Murphy <robin.murphy@arm.com> wrote:
> Hi Sumit,
>
>
> On 21/01/15 04:16, Sumit Semwal wrote:
>>
>> From: Rob Clark <robdclark@gmail.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 <robdclark@gmail.com>
>> [sumits: Minor updates wrt comments on the first version]
>> Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
>> ---
>> include/linux/device.h | 1 +
>> include/linux/dma-mapping.h | 19 +++++++++++++++++++
>> 2 files changed, 20 insertions(+)
>>
>> diff --git a/include/linux/device.h b/include/linux/device.h
>> index fb50673..a32f9b6 100644
>> --- a/include/linux/device.h
>> +++ b/include/linux/device.h
>> @@ -647,6 +647,7 @@ struct device_dma_parameters {
>> * sg limitations.
>> */
>> unsigned int max_segment_size;
>> + unsigned int max_segment_count; /* INT_MAX for unlimited */
>> unsigned long segment_boundary_mask;
>> };
>>
>> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
>> index c3007cb..38e2835 100644
>> --- a/include/linux/dma-mapping.h
>> +++ b/include/linux/dma-mapping.h
>> @@ -154,6 +154,25 @@ static inline unsigned int
>> dma_set_max_seg_size(struct device *dev,
>> return -EIO;
>> }
>>
>> +#define DMA_SEGMENTS_MAX_SEG_COUNT ((unsigned int) INT_MAX)
>> +
>> +static inline unsigned int dma_get_max_seg_count(struct device *dev)
>> +{
>> + return dev->dma_parms ?
>> + dev->dma_parms->max_segment_count :
>> + DMA_SEGMENTS_MAX_SEG_COUNT;
>> +}
>
>
> I know this copies the style of the existing code, but unfortunately it also
> copies the subtle brokenness. Plenty of drivers seem to set up a dma_parms
> struct just for max_segment_size, thus chances are you'll come across a
> max_segment_count of 0 sooner or later. How badly is that going to break
> things? I posted a fix recently[1] having hit this problem with
> segment_boundary_mask in IOMMU code.
>
Thanks very much for reviewing this code; and apologies for missing
your patch that you mentioned here; sure, I will update my patch
accordingly as well.
>> +
>> +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
>
>
> This "else" is just as unnecessary as the other two I've taken out ;)
>
>
> Robin.
>
> [1]:http://article.gmane.org/gmane.linux.kernel.iommu/8175/
>
>
>> + return -EIO;
>> +}
>> +
>> static inline unsigned long dma_get_seg_boundary(struct device *dev)
>> {
>> return dev->dma_parms ?
>>
>
>
BR,
Sumit.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [RFCv2 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms
2015-01-21 17:31 ` Russell King - ARM Linux
@ 2015-01-27 7:04 ` Sumit Semwal
0 siblings, 0 replies; 7+ messages in thread
From: Sumit Semwal @ 2015-01-27 7:04 UTC (permalink / raw)
To: Russell King - ARM Linux
Cc: LKML, linux-media, DRI mailing list, Linaro MM SIG Mailman List,
linux-arm-kernel, linux-mm, Tomasz Stanislawski,
Linaro Kernel Mailman List, Rob Clark, Daniel Vetter,
Marek Szyprowski
Hi Russell!
On 21 January 2015 at 23:01, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Wed, Jan 21, 2015 at 09:46:47AM +0530, Sumit Semwal wrote:
>> +static int calc_constraints(struct device *dev,
>> + struct dma_buf_constraints *calc_cons)
>> +{
>> + struct dma_buf_constraints cons = *calc_cons;
>> +
>> + cons.dma_mask &= dma_get_mask(dev);
>
> I don't think this makes much sense when you consider that the DMA
> infrastructure supports buses with offsets. The DMA mask is th
> upper limit of the _bus_ specific address, it is not a mask per-se.
>
> What this means is that &= is not the right operation. Moreover,
> simply comparing masks which could be from devices on unrelated
> buses doesn't make sense either.
>
> However, that said, I don't have an answer for what you want to
> achieve here.
Thanks for your comments! I suppose in that case, I will leave out the
*dma_masks from this constraints information for now; we can re-visit
it when a specific use case really needs information about the
dma-masks of the attached devices.
I will post an updated patch-set soon.
>
> --
> FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
> according to speedtest.net.
--
Thanks and regards,
Sumit Semwal
Kernel Team Lead - Linaro Mobile Group
Linaro.org │ Open source software for ARM SoCs
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2015-01-27 7:04 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-01-21 4:16 [RFCv2 0/2] dma-parms, constraints and helpers for dma-buf Sumit Semwal
2015-01-21 4:16 ` [RFCv2 1/2] device: add dma_params->max_segment_count Sumit Semwal
2015-01-21 18:56 ` Robin Murphy
2015-01-22 3:46 ` Sumit Semwal
2015-01-21 4:16 ` [RFCv2 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms Sumit Semwal
2015-01-21 17:31 ` Russell King - ARM Linux
2015-01-27 7:04 ` Sumit Semwal
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