Hi Laurent, On 08/15/2012 10:04 PM, Laurent Pinchart wrote: > Hi Tomasz, > > Thanks for the patch. > > On Tuesday 14 August 2012 17:34:51 Tomasz Stanislawski wrote: >> This patch adds taking reference to the device for MMAP buffers. >> >> Such buffers, may be exported using DMABUF mechanism. If the driver that >> created a queue is unloaded then the queue is released, the device might be >> released too. However, buffers cannot be released if they are referenced by >> DMABUF descriptor(s). The device pointer kept in a buffer must be valid for >> the whole buffer's lifetime. Therefore MMAP buffers should take a reference >> to the device to avoid risk of dangling pointers. > > That patch looks good, but that approach won't scale if we ever need a more > complex context that can't be copied. We can ignore that for now, but if we > decide to support "orphan" vb2 buffers, that's an issue we need to be aware of > as it might come back to bite us in the future. > Good news is that vb2-dma-contig knows the structure of the context. Therefore it will always be able to implement a proper 'copy constructor'. One could always add reference counting for contexts but I consider it little over-engineering. > I assume that this patch requires your dmabuf owner patch to fix the orphan > buffer case properly. > The 'dmabuf owner' patch is not required for this patchset. It will only protect 'videobuf2-dma-contig' module from being unloaded while its dmabuf is in use. Regards, Tomasz Stanislawski -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
