[PATCH v5 6/8] drm/panfrost: Support synchronization jobs

[Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>]

Sometimes, all the user wants to do is add a synchronization point.
Userspace can already do that by submitting a NULL job, but this implies
submitting something to the GPU when we could simply skip the job and
signal the done fence directly.

v5:
* New patch

Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/panfrost/panfrost_drv.c | 9 +++++++--
 drivers/gpu/drm/panfrost/panfrost_job.c | 6 ++++++
 include/uapi/drm/panfrost_drm.h         | 7 +++++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
index 30dc158d56e6..89a0c484310c 100644
--- a/drivers/gpu/drm/panfrost/panfrost_drv.c
+++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
@@ -542,7 +542,9 @@ static const struct panfrost_submit_ioctl_version_info submit_versions[] = {
 	[1] = { 48, 8, 16 },
 };
 
-#define PANFROST_JD_ALLOWED_REQS PANFROST_JD_REQ_FS
+#define PANFROST_JD_ALLOWED_REQS \
+	(PANFROST_JD_REQ_FS | \
+	 PANFROST_JD_REQ_DEP_ONLY)
 
 static int
 panfrost_submit_job(struct drm_device *dev, struct drm_file *file_priv,
@@ -559,7 +561,10 @@ panfrost_submit_job(struct drm_device *dev, struct drm_file *file_priv,
 	if (args->requirements & ~PANFROST_JD_ALLOWED_REQS)
 		return -EINVAL;
 
-	if (!args->head)
+	/* If this is a dependency-only job, the job chain head should be NULL,
+	 * otherwise it should be non-NULL.
+	 */
+	if ((args->head != 0) != !(args->requirements & PANFROST_JD_REQ_DEP_ONLY))
 		return -EINVAL;
 
 	bo_stride = submit_versions[version].bo_ref_stride;
diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
index 0367cee8f6df..6d8706d4a096 100644
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -192,6 +192,12 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
 	u64 jc_head = job->jc;
 	int ret;
 
+	if (job->requirements & PANFROST_JD_REQ_DEP_ONLY) {
+		/* Nothing to execute, signal the fence directly. */
+		dma_fence_signal_locked(job->done_fence);
+		return;
+	}
+
 	panfrost_devfreq_record_busy(&pfdev->pfdevfreq);
 
 	ret = pm_runtime_get_sync(pfdev->dev);
diff --git a/include/uapi/drm/panfrost_drm.h b/include/uapi/drm/panfrost_drm.h
index 5e3f8a344f41..b9df066970f6 100644
--- a/include/uapi/drm/panfrost_drm.h
+++ b/include/uapi/drm/panfrost_drm.h
@@ -46,6 +46,13 @@ extern "C" {
 #define DRM_IOCTL_PANFROST_PERFCNT_DUMP		DRM_IOW(DRM_COMMAND_BASE + DRM_PANFROST_PERFCNT_DUMP, struct drm_panfrost_perfcnt_dump)
 
 #define PANFROST_JD_REQ_FS (1 << 0)
+
+/*
+ * Dependency only job. The job chain head should be set to 0 when this flag
+ * is set.
+ */
+#define PANFROST_JD_REQ_DEP_ONLY (1 << 1)
+
 /**
  * struct drm_panfrost_submit - ioctl argument for submitting commands to the 3D
  * engine.
-- 
2.31.1