On Mon, Jan 09, 2012 at 03:20:48PM +0900, InKi Dae wrote: > I has test dmabuf based drm gem module for exynos and I found one problem. > you can refer to this test repository: > http://git.infradead.org/users/kmpark/linux-samsung/shortlog/refs/heads/exynos-drm-dmabuf > > at this repository, I added some exception codes for resource release > in addition to Dave's patch sets. > > let's suppose we use dmabuf based vb2 and drm gem with physically > continuous memory(no IOMMU) and we try to share allocated buffer > between them(v4l2 and drm driver). > > 1. request memory allocation through drm gem interface. > 2. request DRM_SET_PRIME ioctl with the gem handle to get a fd to the > gem object. > - internally, private gem based dmabuf moudle calls drm_buf_export() > to register allocated gem object to fd. > 3. request qbuf with the fd(got from 2) and DMABUF type to set the > buffer to v4l2 based device. > - internally, vb2 plug in module gets a buffer to the fd and then > calls dmabuf->ops->map_dmabuf() callback to get the sg table > containing physical memory info to the gem object. and then the > physical memory info would be copied to vb2_xx_buf object. > for DMABUF feature for v4l2 and videobuf2 framework, you can refer to > this repository: > git://github.com/robclark/kernel-omap4.git drmplane-dmabuf > > after that, if v4l2 driver want to release vb2_xx_buf object with > allocated memory region by user request, how should we do?. refcount > to vb2_xx_buf is dependent on videobuf2 framework. so when vb2_xx_buf > object is released videobuf2 framework don't know who is using the > physical memory region. so this physical memory region is released and > when drm driver tries to access the region or to release it also, a > problem would be induced. > > for this problem, I added get_shared_cnt() callback to dma-buf.h but > I'm not sure that this is good way. maybe there may be better way. > if there is any missing point, please let me know. The dma_buf object needs to hold a reference on the underlying (necessarily reference-counted) buffer object when the exporter creates the dma_buf handle. This reference should then get dropped in the exporters dma_buf->ops->release() function, which is only getting called when the last reference to the dma_buf disappears. If this doesn't work like that currently, we have a bug, and exporting the reference count or something similar can't fix that. Yours, Daniel PS: Please cut down the original mail when replying, otherwise it's pretty hard to find your response ;-) -- Daniel Vetter Mail: daniel@xxxxxxxx Mobile: +41 (0)79 365 57 48 -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>