Op 28-09-12 14:42, Maarten Lankhorst schreef: > A fence can be attached to a buffer which is being filled or consumed > by hw, to allow userspace to pass the buffer without waiting to another > device. For example, userspace can call page_flip ioctl to display the > next frame of graphics after kicking the GPU but while the GPU is still > rendering. The display device sharing the buffer with the GPU would > attach a callback to get notified when the GPU's rendering-complete IRQ > fires, to update the scan-out address of the display, without having to > wake up userspace. > > A fence is transient, one-shot deal. It is allocated and attached > to one or more dma-buf's. When the one that attached it is done, with > the pending operation, it can signal the fence: > + fence_signal() > > To have a rough approximation whether a fence is fired, call: > + fence_is_signaled() > > The dma-buf-mgr handles tracking, and waiting on, the fences associated > with a dma-buf. > > The one pending on the fence can add an async callback: > + fence_add_callback() > > The callback can optionally be cancelled with: > + fence_remove_callback() > > To wait synchronously, optionally with a timeout: > + fence_wait() > + fence_wait_timeout() > ... Implementing this makes the locking feel weird, instead of abusing fence->event_queue.lock I think it would make sense to remove this part entirely, and have a simply linked list plus a pointer to a spinlock. enable_signaling should be called with this spinlock held. This way, the enable_signaling callback would be easier to implement and doesn't have to double check for races as much in there. Also __fence_signal should be exported which would be the same as fence_signal, but without taking the spinlock as separate step, so it can be called with the spinlock held. How do you feel about these proposed changes? ~Maarten -- 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
