From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mailout2.w1.samsung.com ([210.118.77.12]:20970 "EHLO mailout2.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756112Ab2AYRCq (ORCPT ); Wed, 25 Jan 2012 12:02:46 -0500 Date: Wed, 25 Jan 2012 18:02:41 +0100 From: Tomasz Stanislawski Subject: Re: [PATCH 1/3] dma-buf: Introduce dma buffer sharing mechanism In-reply-to: <1324891397-10877-2-git-send-email-sumit.semwal@ti.com> To: Sumit Semwal Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linaro-mm-sig@lists.linaro.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, arnd@arndb.de, airlied@redhat.com, linux@arm.linux.org.uk, jesse.barker@linaro.org, m.szyprowski@samsung.com, rob@ti.com, daniel@ffwll.ch, patches@linaro.org, Sumit Semwal Message-id: <4F2035B1.4020204@samsung.com> MIME-version: 1.0 Content-type: text/plain; charset=ISO-8859-1; format=flowed Content-transfer-encoding: 7BIT References: <1324891397-10877-1-git-send-email-sumit.semwal@ti.com> <1324891397-10877-2-git-send-email-sumit.semwal@ti.com> Sender: linux-media-owner@vger.kernel.org List-ID: Hi Sumit, On 12/26/2011 10:23 AM, 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. > [snip] > +/** > + * struct dma_buf_attachment - holds device-buffer attachment data > + * @dmabuf: buffer for this attachment. > + * @dev: device attached to the buffer. > + * @node: list of dma_buf_attachment. > + * @priv: exporter specific attachment data. > + * > + * This structure holds the attachment information between the dma_buf buffer > + * and its user device(s). The list contains one attachment struct per device > + * attached to the buffer. > + */ > +struct dma_buf_attachment { > + struct dma_buf *dmabuf; > + struct device *dev; > + struct list_head node; > + void *priv; > +}; > + > +#ifdef CONFIG_DMA_SHARED_BUFFER > +struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, > + struct device *dev); > +void dma_buf_detach(struct dma_buf *dmabuf, > + struct dma_buf_attachment *dmabuf_attach); > +struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops, > + size_t size, int flags); > +int dma_buf_fd(struct dma_buf *dmabuf); > +struct dma_buf *dma_buf_get(int fd); > +void dma_buf_put(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 *); I think that you should add enum dma_data_direction as an argument unmap function. It was mentioned that the dma_buf_attachment should keep cached and mapped sg_table for performance reasons. The field dma_buf_attachment::priv seams to be a natural place to keep this sg_table. To map a buffer the exporter calls dma_map_sg. It needs dma direction as an argument. The problem is that dma_unmap_sg also needs this argument but dma direction is not available neither in dma_buf_unmap_attachment nor in unmap callback. Therefore the exporter is forced to embed returned sg_table into a bigger structure where dma direction is remembered. Refer to function vb2_dc_dmabuf_ops_map at link below as an example: http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/43793/focus=43797 Regards, Tomasz Stanislawski