On Mon, Jan 23, 2012 at 10:06:57AM +0100, Marek Szyprowski wrote: > Hello, > > On Friday, January 20, 2012 5:29 PM Laurent Pinchart wrote: > > > On Friday 20 January 2012 17:20:22 Tomasz Stanislawski wrote: > > > >> IMO, One way to do this is adding field 'struct device *dev' to struct > > > >> vb2_queue. This field should be filled by a driver prior to calling > > > >> vb2_queue_init. > > > > > > > > I haven't looked into the details, but that sounds good to me. Do we have > > > > use cases where a queue is allocated before knowing which physical > > > > device it will be used for ? > > > > > > I don't think so. In case of S5P drivers, vb2_queue_init is called while > > > opening /dev/videoX. > > > > > > BTW. This struct device may help vb2 to produce logs with more > > > descriptive client annotation. > > > > > > What happens if such a device is NULL. It would happen for vmalloc > > > allocator used by VIVI? > > > > Good question. Should dma-buf accept NULL devices ? Or should vivi pass its > > V4L2 device to vb2 ? > > I assume you suggested using struct video_device->dev entry in such case. > It will not work. DMA-mapping API requires some parameters to be set for the > client device, like for example dma mask. struct video_device contains only an > artificial struct device entry, which has no relation to any physical device > and cannot be used for calling DMA-mapping functions. > > Performing dma_map_* operations with such artificial struct device doesn't make > any sense. It also slows down things significantly due to cache flushing > (forced by dma-mapping) which should be avoided if the buffer is accessed only > with CPU (like it is done by vb2-vmalloc style drivers). > > IMHO this case perfectly shows the design mistake that have been made. The > current version simply tries to do too much. Nope, the current dma_buf does too little. Atm it's simple not useable for drivers that need cpu access, at least not if you're willing to resort to ugly an non-portable tricks like prime. We've discussed this quite a bit and decided that solving cpu access and coherency with n other devices involved is too much v1. It looks like we need to add that extension rather sooner than later. -Daniel -- Daniel Vetter Mail: daniel@xxxxxxxx Mobile: +41 (0)79 365 57 48 -- 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
