dma-buf: add poll support, v3

Thanks to Fengguang Wu for spotting a missing static cast.

v2:
- Kill unused variable need_shared.
v3:
- Clarify the BUG() in dma_buf_release some more. (Rob Clark)
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/dma-buf/dma-buf.c

@@ -30,6 +30,7 @@
 #include <linux/export.h>
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
+#include <linux/poll.h>
 #include <linux/reservation.h>
 
 static inline int is_dma_buf_file(struct file *);
@@ -52,6 +53,16 @@ static int dma_buf_release(struct inode *inode, struct file *file)
 
 	BUG_ON(dmabuf->vmapping_counter);
 
+	/*
+	 * Any fences that a dma-buf poll can wait on should be signaled
+	 * before releasing dma-buf. This is the responsibility of each
+	 * driver that uses the reservation objects.
+	 *
+	 * If you hit this BUG() it means someone dropped their ref to the
+	 * dma-buf while still having pending operation to the buffer.
+	 */
+	BUG_ON(dmabuf->cb_shared.active || dmabuf->cb_excl.active);
+
 	dmabuf->ops->release(dmabuf);
 
 	mutex_lock(&db_list.lock);
@@ -108,10 +119,103 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
 	return base + offset;
 }
 
+static void dma_buf_poll_cb(struct fence *fence, struct fence_cb *cb)
+{
+	struct dma_buf_poll_cb_t *dcb = (struct dma_buf_poll_cb_t *)cb;
+	unsigned long flags;
+
+	spin_lock_irqsave(&dcb->poll->lock, flags);
+	wake_up_locked_poll(dcb->poll, dcb->active);
+	dcb->active = 0;
+	spin_unlock_irqrestore(&dcb->poll->lock, flags);
+}
+
+static unsigned int dma_buf_poll(struct file *file, poll_table *poll)
+{
+	struct dma_buf *dmabuf;
+	struct reservation_object *resv;
+	unsigned long events;
+
+	dmabuf = file->private_data;
+	if (!dmabuf || !dmabuf->resv)
+		return POLLERR;
+
+	resv = dmabuf->resv;
+
+	poll_wait(file, &dmabuf->poll, poll);
+
+	events = poll_requested_events(poll) & (POLLIN | POLLOUT);
+	if (!events)
+		return 0;
+
+	ww_mutex_lock(&resv->lock, NULL);
+
+	if (resv->fence_excl && (!(events & POLLOUT) ||
+				 resv->fence_shared_count == 0)) {
+		struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_excl;
+		unsigned long pevents = POLLIN;
+
+		if (resv->fence_shared_count == 0)
+			pevents |= POLLOUT;
+
+		spin_lock_irq(&dmabuf->poll.lock);
+		if (dcb->active) {
+			dcb->active |= pevents;
+			events &= ~pevents;
+		} else
+			dcb->active = pevents;
+		spin_unlock_irq(&dmabuf->poll.lock);
+
+		if (events & pevents) {
+			if (!fence_add_callback(resv->fence_excl,
+						&dcb->cb, dma_buf_poll_cb))
+				events &= ~pevents;
+			else
+				/*
+				 * No callback queued, wake up any additional
+				 * waiters.
+				 */
+				dma_buf_poll_cb(NULL, &dcb->cb);
+		}
+	}
+
+	if ((events & POLLOUT) && resv->fence_shared_count > 0) {
+		struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_shared;
+		int i;
+
+		/* Only queue a new callback if no event has fired yet */
+		spin_lock_irq(&dmabuf->poll.lock);
+		if (dcb->active)
+			events &= ~POLLOUT;
+		else
+			dcb->active = POLLOUT;
+		spin_unlock_irq(&dmabuf->poll.lock);
+
+		if (!(events & POLLOUT))
+			goto out;
+
+		for (i = 0; i < resv->fence_shared_count; ++i)
+			if (!fence_add_callback(resv->fence_shared[i],
+						&dcb->cb, dma_buf_poll_cb)) {
+				events &= ~POLLOUT;
+				break;
+			}
+
+		/* No callback queued, wake up any additional waiters. */
+		if (i == resv->fence_shared_count)
+			dma_buf_poll_cb(NULL, &dcb->cb);
+	}
+
+out:
+	ww_mutex_unlock(&resv->lock);
+	return events;
+}
+
 static const struct file_operations dma_buf_fops = {
 	.release	= dma_buf_release,
 	.mmap		= dma_buf_mmap_internal,
 	.llseek		= dma_buf_llseek,
+	.poll		= dma_buf_poll,
 };
 
 /*
@@ -171,6 +275,10 @@ struct dma_buf *dma_buf_export_named(void *priv, const struct dma_buf_ops *ops,
 	dmabuf->ops = ops;
 	dmabuf->size = size;
 	dmabuf->exp_name = exp_name;
+	init_waitqueue_head(&dmabuf->poll);
+	dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll;
+	dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0;
+
 	if (!resv) {
 		resv = (struct reservation_object *)&dmabuf[1];
 		reservation_object_init(resv);

include/linux/dma-buf.h

@@ -30,6 +30,8 @@
 #include <linux/list.h>
 #include <linux/dma-mapping.h>
 #include <linux/fs.h>
+#include <linux/fence.h>
+#include <linux/wait.h>
 
 struct device;
 struct dma_buf;
@@ -130,6 +132,16 @@ struct dma_buf {
 	struct list_head list_node;
 	void *priv;
 	struct reservation_object *resv;
+
+	/* poll support */
+	wait_queue_head_t poll;
+
+	struct dma_buf_poll_cb_t {
+		struct fence_cb cb;
+		wait_queue_head_t *poll;
+
+		unsigned long active;
+	} cb_excl, cb_shared;
 };
 
 /**