[PATCH v2 7/9] dma-buf: add poll support, v3

Maarten Lankhorst
2014-07-01T10:57:43Z

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>
---
drivers/dma-buf/dma-buf.c | 108 +++++++++++++++++++++++++++++++++++++++++++++
include/linux/dma-buf.h | 12 +++++
2 files changed, 120 insertions(+)

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);
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index fd7def2e0ae2..694e1fe1c4b4 100644
--- a/include/linux/dma-buf.h
+++ b/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;
};

/**