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>

1 files changed, 108 insertions, 0 deletions

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index cd40ca22911f..25e8c4165936 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/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);