On Tue, Mar 25, 2014 at 7:40 PM, David Herrmann <dh.herrmann@xxxxxxxxx> wrote: > Hi > > On Tue, Mar 25, 2014 at 9:01 AM, Daniel Vetter <daniel@xxxxxxxx> wrote: >> Besides the issue at hand though I think drivers need to make sure >> that the device they use for attaching does outlive the dma-buf. Which >> for real hotpluggin probably means that drivers need to drop all >> attachment on unplug (the dma mapping is useless anyway) and just keep >> all their imported gem objects alive with just a reference to the >> dma-buf object itself. > > Drivers should never touch other drivers or even look at them. There > is no reason i915 is responsible of keeping udl alive. That gets > really messy and may introduce circular dependencies. > > I'd like to see exported dma-bufs reference their drm-device owner. > This way, the drm-device stays around until the dma-buf is removed. To > avoid lazy device destruction, a driver can (during unplug) simply > detach all dma-bufs if, and only if, they first made the dma-buf > somehow stand-alone. > > For example: udl can just move the allocated pages into the dma-buf, > mark it as dead and detach it. The udl-device can get destructed and > whenever i915 releases the dma-buf, the udl-dma-buf ops see it's dead > and just deref it / release dma-buf resources. But this is all not > needed if the exported dma-bufs just reference "drm_device", which is > imho the easiest fix. I sent a patch to fix the udl case to just keep a reference on the usb_interface device it seems to work, we probably do need to do this in theory for pci devices as well in a hotplug/sysfs plug situation I suppose, Dave. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
