dma-buf/sync_file: Add SET_DEADLINE ioctl

The initial purpose is for igt tests, but this would also be useful for
compositors that wait until close to vblank deadline to make decisions
about which frame to show.

The igt tests can be found at:

https://gitlab.freedesktop.org/robclark/igt-gpu-tools/-/commits/fence-deadline

v2: Clarify the timebase, add link to igt tests
v3: Use u64 value in ns to express deadline.
v4: More doc

Signed-off-by: Rob Clark <robdclark@chromium.org>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230823215458.203366-3-robdclark@gmail.com

Author: robclark

drivers/dma-buf/dma-fence.c

@@ -934,7 +934,8 @@ EXPORT_SYMBOL(dma_fence_wait_any_timeout);
  *   the GPU's devfreq to reduce frequency, when in fact the opposite is what is
  *   needed.
  *
- * To this end, deadline hint(s) can be set on a &dma_fence via &dma_fence_set_deadline.
+ * To this end, deadline hint(s) can be set on a &dma_fence via &dma_fence_set_deadline
+ * (or indirectly via userspace facing ioctls like &sync_set_deadline).
  * The deadline hint provides a way for the waiting driver, or userspace, to
  * convey an appropriate sense of urgency to the signaling driver.
  *

drivers/dma-buf/sync_file.c

@@ -347,6 +347,22 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
 	return ret;
 }
 
+static int sync_file_ioctl_set_deadline(struct sync_file *sync_file,
+					unsigned long arg)
+{
+	struct sync_set_deadline ts;
+
+	if (copy_from_user(&ts, (void __user *)arg, sizeof(ts)))
+		return -EFAULT;
+
+	if (ts.pad)
+		return -EINVAL;
+
+	dma_fence_set_deadline(sync_file->fence, ns_to_ktime(ts.deadline_ns));
+
+	return 0;
+}
+
 static long sync_file_ioctl(struct file *file, unsigned int cmd,
 			    unsigned long arg)
 {
@@ -359,6 +375,9 @@ static long sync_file_ioctl(struct file *file, unsigned int cmd,
 	case SYNC_IOC_FILE_INFO:
 		return sync_file_ioctl_fence_info(sync_file, arg);
 
+	case SYNC_IOC_SET_DEADLINE:
+		return sync_file_ioctl_set_deadline(sync_file, arg);
+
 	default:
 		return -ENOTTY;
 	}

include/uapi/linux/sync_file.h

@@ -76,6 +76,27 @@ struct sync_file_info {
 	__u64	sync_fence_info;
 };
 
+/**
+ * struct sync_set_deadline - SYNC_IOC_SET_DEADLINE - set a deadline hint on a fence
+ * @deadline_ns: absolute time of the deadline
+ * @pad:	must be zero
+ *
+ * Allows userspace to set a deadline on a fence, see &dma_fence_set_deadline
+ *
+ * The timebase for the deadline is CLOCK_MONOTONIC (same as vblank).  For
+ * example
+ *
+ *     clock_gettime(CLOCK_MONOTONIC, &t);
+ *     deadline_ns = (t.tv_sec * 1000000000L) + t.tv_nsec + ns_until_deadline
+ */
+struct sync_set_deadline {
+	__u64	deadline_ns;
+	/* Not strictly needed for alignment but gives some possibility
+	 * for future extension:
+	 */
+	__u64	pad;
+};
+
 #define SYNC_IOC_MAGIC		'>'
 
 /*
@@ -87,5 +108,6 @@ struct sync_file_info {
 
 #define SYNC_IOC_MERGE		_IOWR(SYNC_IOC_MAGIC, 3, struct sync_merge_data)
 #define SYNC_IOC_FILE_INFO	_IOWR(SYNC_IOC_MAGIC, 4, struct sync_file_info)
+#define SYNC_IOC_SET_DEADLINE	_IOW(SYNC_IOC_MAGIC, 5, struct sync_set_deadline)
 
 #endif /* _UAPI_LINUX_SYNC_H */