gpu: nvgpu: clarify fence api assumptions

Adjust documentation and validity checks in the fence functions for
simplicity.

Now that the cde code is using user fences cleanly, the
do-nothing-on-null action can cause unintended behaviour in new code
using nvgpu_fence_get and nvgpu_fence_put. It does not make sense to
call these with a null fence, so delete the checks.

Extend the documentation in nvgpu_fence_extract_user() for the os fence
lifetime to give a reason for the dup call.

Make nvgpu_fence_from_semaphore() and nvgpu_fence_from_syncpt() return
void. These fill a previously allocated object; the only failure would
have been a null object, but that never happens and is not acceptable
behaviour for callers so delete these null checks and fix types.

Jira NVGPU-5248

Change-Id: I9f82365d50ab5600374c8f7dd513691eac14a2f1
Signed-off-by: Konsta Hölttä <kholtta@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2359624
Reviewed-by: svc-mobile-coverity <svc-mobile-coverity@nvidia.com>
Reviewed-by: svc-mobile-misra <svc-mobile-misra@nvidia.com>
Reviewed-by: svc-mobile-cert <svc-mobile-cert@nvidia.com>
Reviewed-by: Alex Waterman <alexw@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
GVS: Gerrit_Virtual_Submit
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/common/fence/fence.c

@@ -63,16 +63,12 @@ static void nvgpu_fence_free(struct nvgpu_ref *ref)
 
 void nvgpu_fence_put(struct nvgpu_fence_type *f)
 {
-	if (f != NULL) {
 	nvgpu_ref_put(&f->ref, nvgpu_fence_free);
-	}
 }
 
 struct nvgpu_fence_type *nvgpu_fence_get(struct nvgpu_fence_type *f)
 {
-	if (f != NULL) {
 	nvgpu_ref_get(&f->ref);
-	}
 	return f;
 }
 
@@ -89,8 +85,11 @@ struct nvgpu_user_fence nvgpu_fence_extract_user(struct nvgpu_fence_type *f)
 	};
 
 	/*
-	 * Keep our ref to the os fence for now so that the user fence can be
+	 * The os fence member has to live so it can be signaled when the job
-	 * extracted multiple times (for cde).
+	 * completes. The returned user fence may live longer than that before
+	 * being safely attached to an fd if the job completes before a
+	 * submission ioctl finishes, or if it's stored for cde job state
+	 * tracking.
 	 */
 	if (nvgpu_os_fence_is_initialized(&f->os_fence)) {
 		f->os_fence.ops->dup(&f->os_fence);
@@ -188,9 +187,6 @@ void nvgpu_fence_init(struct nvgpu_fence_type *f,
 		const struct nvgpu_fence_ops *ops,
 		struct nvgpu_os_fence os_fence)
 {
-	if (f == NULL) {
-		return;
-	}
 	f->ops = ops;
 	f->syncpt_id = NVGPU_INVALID_SYNCPT_ID;
 #ifdef CONFIG_NVGPU_SW_SEMAPHORE
@@ -225,24 +221,16 @@ static const struct nvgpu_fence_ops nvgpu_semaphore_fence_ops = {
 };
 
 /* This function takes ownership of the semaphore as well as the os_fence */
-int nvgpu_fence_from_semaphore(
+void nvgpu_fence_from_semaphore(
-		struct nvgpu_fence_type *fence_out,
+		struct nvgpu_fence_type *f,
 		struct nvgpu_semaphore *semaphore,
 		struct nvgpu_cond *semaphore_wq,
 		struct nvgpu_os_fence os_fence)
 {
-	struct nvgpu_fence_type *f = fence_out;
-
 	nvgpu_fence_init(f, &nvgpu_semaphore_fence_ops, os_fence);
-	if (f == NULL) {
-		return -EINVAL;
-	}
-
 
 	f->semaphore = semaphore;
 	f->semaphore_wq = semaphore_wq;
-
-	return 0;
 }
 
 #endif
@@ -286,30 +274,15 @@ static const struct nvgpu_fence_ops nvgpu_fence_syncpt_ops = {
 };
 
 /* This function takes the ownership of the os_fence */
-int nvgpu_fence_from_syncpt(
+void nvgpu_fence_from_syncpt(
-		struct nvgpu_fence_type *fence_out,
+		struct nvgpu_fence_type *f,
 		struct nvgpu_nvhost_dev *nvhost_dev,
 		u32 id, u32 value, struct nvgpu_os_fence os_fence)
 {
-	struct nvgpu_fence_type *f = fence_out;
-
 	nvgpu_fence_init(f, &nvgpu_fence_syncpt_ops, os_fence);
-	if (!f) {
-		return -EINVAL;
-	}
 
 	f->nvhost_dev = nvhost_dev;
 	f->syncpt_id = id;
 	f->syncpt_value = value;
-
-	return 0;
-}
-#else
-int nvgpu_fence_from_syncpt(
-		struct nvgpu_fence_type *fence_out,
-		struct nvgpu_nvhost_dev *nvhost_dev,
-		u32 id, u32 value, struct nvgpu_os_fence os_fence)
-{
-	return -EINVAL;
 }
 #endif

drivers/gpu/nvgpu/common/sync/channel_sync_semaphore.c

@@ -213,19 +213,10 @@ static int channel_sync_semaphore_incr_common(
 		}
 	}
 
-	err = nvgpu_fence_from_semaphore(fence, semaphore, &c->semaphore_wq,
+	nvgpu_fence_from_semaphore(fence, semaphore, &c->semaphore_wq, os_fence);
-			os_fence);
-
-	if (err != 0) {
-		goto clean_up_os_fence;
-	}
 
 	return 0;
 
-clean_up_os_fence:
-	if (nvgpu_os_fence_is_initialized(&os_fence)) {
-		os_fence.ops->drop_ref(&os_fence);
-	}
 clean_up_cmdbuf:
 	nvgpu_priv_cmdbuf_rollback(c->priv_cmd_q, *incr_cmd);
 clean_up_sema:

drivers/gpu/nvgpu/common/sync/channel_sync_syncpt.c

@@ -216,15 +216,7 @@ static int channel_sync_syncpt_incr_common(struct nvgpu_channel_sync *s,
 		}
 	}
 
-	err = nvgpu_fence_from_syncpt(fence, sp->nvhost,
+	nvgpu_fence_from_syncpt(fence, sp->nvhost, sp->id, thresh, os_fence);
-	 sp->id, thresh, os_fence);
-
-	if (err != 0) {
-		if (nvgpu_os_fence_is_initialized(&os_fence) != 0) {
-			os_fence.ops->drop_ref(&os_fence);
-		}
-		goto clean_up_priv_cmd;
-	}
 
 	return 0;
 

drivers/gpu/nvgpu/include/nvgpu/fence.h

@@ -67,15 +67,15 @@ struct nvgpu_fence_ops {
 
 #ifdef CONFIG_NVGPU_SW_SEMAPHORE
 /* Fences can be created from semaphores or syncpoint (id, value) pairs */
-int nvgpu_fence_from_semaphore(
+void nvgpu_fence_from_semaphore(
-		struct nvgpu_fence_type *fence_out,
+		struct nvgpu_fence_type *f,
 		struct nvgpu_semaphore *semaphore,
 		struct nvgpu_cond *semaphore_wq,
 		struct nvgpu_os_fence os_fence);
 #endif
 
-int nvgpu_fence_from_syncpt(
+void nvgpu_fence_from_syncpt(
-		struct nvgpu_fence_type *fence_out,
+		struct nvgpu_fence_type *f,
 		struct nvgpu_nvhost_dev *nvhost_dev,
 		u32 id, u32 value,
 		struct nvgpu_os_fence os_fence);