Re: [PATCH 2/2] dma-buf: add helpers for attacher dma-parms
From: Tomasz Stanislawski <hidden>
Date: 2012-08-06 10:29:41
Also in:
dri-devel, linux-arm-kernel, linux-media, lkml
Hi Rob, On 07/19/2012 06:23 PM, Rob Clark wrote:
quoted hunk ↗ jump to hunk
From: Rob Clark <redacted> Add some helpers to iterate through all attachers and get the most restrictive segment size/count/boundary. Signed-off-by: Rob Clark <redacted> --- 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.
quoted hunk ↗ jump to hunk
+ 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
quoted hunk ↗ jump to hunk
+ 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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