Hi Summit, Sorry for the late review. I know that this code is now in mainline, but I still have a couple of comments. I'll send patches if you agree with them. On Monday 26 December 2011 10:23:15 Sumit Semwal wrote: > This is the first step in defining a dma buffer sharing mechanism. > > A new buffer object dma_buf is added, with operations and API to allow easy > sharing of this buffer object across devices. > > The framework allows: > - creation of a buffer object, its association with a file pointer, and > associated allocator-defined operations on that buffer. This operation > is called the 'export' operation. > - different devices to 'attach' themselves to this exported buffer object, > to facilitate backing storage negotiation, using dma_buf_attach() API. - > the exported buffer object to be shared with the other entity by asking > for its 'file-descriptor (fd)', and sharing the fd across. > - a received fd to get the buffer object back, where it can be accessed > using the associated exporter-defined operations. > - the exporter and user to share the scatterlist associated with this > buffer object using map_dma_buf and unmap_dma_buf operations. > > Atleast one 'attach()' call is required to be made prior to calling the > map_dma_buf() operation. > > Couple of building blocks in map_dma_buf() are added to ease introduction > of sync'ing across exporter and users, and late allocation by the exporter. > > For this first version, this framework will work with certain conditions: > - *ONLY* exporter will be allowed to mmap to userspace (outside of this > framework - mmap is not a buffer object operation), > - currently, *ONLY* users that do not need CPU access to the buffer are > allowed. > > More details are there in the documentation patch. > > This is based on design suggestions from many people at the > mini-summits[1], most notably from Arnd Bergmann <arnd@xxxxxxxx>, Rob > Clark <rob@xxxxxx> and Daniel Vetter <daniel@xxxxxxxx>. > > The implementation is inspired from proof-of-concept patch-set from > Tomasz Stanislawski <t.stanislaws@xxxxxxxxxxx>, who demonstrated buffer > sharing between two v4l2 devices. [2] > > [1]: https://wiki.linaro.org/OfficeofCTO/MemoryManagement > [2]: http://lwn.net/Articles/454389 > > Signed-off-by: Sumit Semwal <sumit.semwal@xxxxxxxxxx> > Signed-off-by: Sumit Semwal <sumit.semwal@xxxxxx> > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > Reviewed-by: Dave Airlie <airlied@xxxxxxxxxx> > Reviewed-and-Tested-by: Rob Clark <rob.clark@xxxxxxxxxx> > --- > drivers/base/Kconfig | 10 ++ > drivers/base/Makefile | 1 + > drivers/base/dma-buf.c | 291 > +++++++++++++++++++++++++++++++++++++++++++++++ include/linux/dma-buf.h | > 176 ++++++++++++++++++++++++++++ > 4 files changed, 478 insertions(+), 0 deletions(-) > create mode 100644 drivers/base/dma-buf.c > create mode 100644 include/linux/dma-buf.h > [snip] > diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c > new file mode 100644 > index 0000000..e38ad24 > --- /dev/null > +++ b/drivers/base/dma-buf.c > @@ -0,0 +1,291 @@ [snip] > +/** > + * dma_buf_export - Creates a new dma_buf, and associates an anon file > + * with this buffer, so it can be exported. > + * Also connect the allocator specific data and ops to the buffer. > + * > + * @priv: [in] Attach private data of allocator to this buffer > + * @ops: [in] Attach allocator-defined dma buf ops to the new buffer. > + * @size: [in] Size of the buffer > + * @flags: [in] mode flags for the file. > + * > + * Returns, on success, a newly created dma_buf object, which wraps the > + * supplied private data and operations for dma_buf_ops. On either missing > + * ops, or error in allocating struct dma_buf, will return negative error. > + * > + */ > +struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops, > + size_t size, int flags) > +{ > + struct dma_buf *dmabuf; > + struct file *file; > + > + if (WARN_ON(!priv || !ops > + || !ops->map_dma_buf > + || !ops->unmap_dma_buf > + || !ops->release)) { > + return ERR_PTR(-EINVAL); > + } > + > + dmabuf = kzalloc(sizeof(struct dma_buf), GFP_KERNEL); > + if (dmabuf == NULL) > + return ERR_PTR(-ENOMEM); > + > + dmabuf->priv = priv; > + dmabuf->ops = ops; dmabuf->ops will never but NULL, but (see below) > + dmabuf->size = size; > + > + file = anon_inode_getfile("dmabuf", &dma_buf_fops, dmabuf, flags); > + > + dmabuf->file = file; > + > + mutex_init(&dmabuf->lock); > + INIT_LIST_HEAD(&dmabuf->attachments); > + > + return dmabuf; > +} > +EXPORT_SYMBOL_GPL(dma_buf_export); [snip] > +/** > + * 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. > + * @dev: [in] device to be attached. > + * > + * Returns struct dma_buf_attachment * for this attachment; may return > negative + * error codes. > + * > + */ > +struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, > + struct device *dev) > +{ > + struct dma_buf_attachment *attach; > + int ret; > + > + if (WARN_ON(!dmabuf || !dev || !dmabuf->ops)) you still check dmabuf->ops here, as well as in several places below. Shouldn't these checks be removed ? > + return ERR_PTR(-EINVAL); > + > + attach = kzalloc(sizeof(struct dma_buf_attachment), GFP_KERNEL); > + if (attach == NULL) > + goto err_alloc; What about returning ERR_PTR(-ENOMEM) directly here ? > + > + mutex_lock(&dmabuf->lock); > + > + attach->dev = dev; > + attach->dmabuf = dmabuf; These two lines can be moved before mutex_lock(). > + if (dmabuf->ops->attach) { > + ret = dmabuf->ops->attach(dmabuf, dev, attach); > + if (ret) > + goto err_attach; > + } > + list_add(&attach->node, &dmabuf->attachments); > + > + mutex_unlock(&dmabuf->lock); > + return attach; > + > +err_alloc: > + return ERR_PTR(-ENOMEM); > +err_attach: > + kfree(attach); > + mutex_unlock(&dmabuf->lock); > + return ERR_PTR(ret); > +} > +EXPORT_SYMBOL_GPL(dma_buf_attach); -- Regards, Laurent Pinchart -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . 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