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(-)
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 ?
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 ?
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;} elseThis "else" is just as unnecessary as the other two I've taken out ;)
Robin.
return -EIO;+}
- static inline unsigned long dma_get_seg_boundary(struct device *dev) { return dev->dma_parms ?
BR, Sumit.
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__ */
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.
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.
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Robin Murphy -
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Sumit Semwal