[RFC PATCH] drm/xe: PM snippet

[Matthew Brost]

Code snippet for [1] as guide as to where to add PM refs.

[1] https://patchwork.freedesktop.org/series/128044/
---
 drivers/gpu/drm/xe/xe_gt.c         |  3 +++
 drivers/gpu/drm/xe/xe_guc_ct.c     | 20 ++++++++++++++++++++
 drivers/gpu/drm/xe/xe_guc_submit.c |  4 ++++
 drivers/gpu/drm/xe/xe_pt.c         | 10 ++++++++++
 4 files changed, 37 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_gt.c b/drivers/gpu/drm/xe/xe_gt.c
index 3af2adec1295..f829a1f59d42 100644
--- a/drivers/gpu/drm/xe/xe_gt.c
+++ b/drivers/gpu/drm/xe/xe_gt.c
@@ -604,6 +604,7 @@ static int gt_reset(struct xe_gt *gt)
 		goto err_fail;
 	}
 
+	/* PM get */
 	xe_gt_sanitize(gt);
 
 	xe_device_mem_access_get(gt_to_xe(gt));
@@ -630,6 +631,7 @@ static int gt_reset(struct xe_gt *gt)
 		goto err_out;
 
 	err = xe_force_wake_put(gt_to_fw(gt), XE_FORCEWAKE_ALL);
+	/* PM put */
 	xe_device_mem_access_put(gt_to_xe(gt));
 	XE_WARN_ON(err);
 
@@ -641,6 +643,7 @@ static int gt_reset(struct xe_gt *gt)
 	XE_WARN_ON(xe_force_wake_put(gt_to_fw(gt), XE_FORCEWAKE_ALL));
 err_msg:
 	XE_WARN_ON(xe_uc_start(&gt->uc));
+	/* PM put */
 	xe_device_mem_access_put(gt_to_xe(gt));
 err_fail:
 	xe_gt_err(gt, "reset failed (%pe)\n", ERR_PTR(err));
diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
index c29f095aa1b9..fdc25b076758 100644
--- a/drivers/gpu/drm/xe/xe_guc_ct.c
+++ b/drivers/gpu/drm/xe/xe_guc_ct.c
@@ -307,6 +307,14 @@ int xe_guc_ct_enable(struct xe_guc_ct *ct)
 
 	mutex_lock(&ct->lock);
 	spin_lock_irq(&ct->fast_lock);
+	/*
+	 *  Drop ct->g2h_outstanding PM refs here, it is expected that we will
+	 *  not transition to zero here. Note this changing with [1] but the
+	 *  idea anytime this is set zero, drop the number of PM refs by the
+	 *  initial value and transitioning to zero is not expected.
+	 *
+	 * [1] https://patchwork.freedesktop.org/series/128062/
+	 */
 	ct->g2h_outstanding = 0;
 	ct->enabled = true;
 	spin_unlock_irq(&ct->fast_lock);
@@ -388,7 +396,13 @@ static void __g2h_reserve_space(struct xe_guc_ct *ct, u32 g2h_len, u32 num_g2h)
 
 		ct->ctbs.g2h.info.space -= g2h_len;
 		ct->g2h_outstanding += num_g2h;
+		/*
+		 * If it is safe, ct->lock & ct->fast_lock are held, dma fencing
+		 * path, take num_g2h PM refs here. It should be expected that
+		 * we have at least 1.
+		 */
 	}
+
 }
 
 static void __g2h_release_space(struct xe_guc_ct *ct, u32 g2h_len)
@@ -399,6 +413,12 @@ static void __g2h_release_space(struct xe_guc_ct *ct, u32 g2h_len)
 
 	ct->ctbs.g2h.info.space += g2h_len;
 	--ct->g2h_outstanding;
+
+	/*
+	 * If it is safe, ct->fast_lock is held, possible IRQ context, dma
+	 * fencing path, drop 1 PM ref here. The PM ref can transition to zero
+	 * here.
+	 */
 }
 
 static void g2h_release_space(struct xe_guc_ct *ct, u32 g2h_len)
diff --git a/drivers/gpu/drm/xe/xe_guc_submit.c b/drivers/gpu/drm/xe/xe_guc_submit.c
index 54ffcfcdd41f..a64768257d51 100644
--- a/drivers/gpu/drm/xe/xe_guc_submit.c
+++ b/drivers/gpu/drm/xe/xe_guc_submit.c
@@ -1168,6 +1168,8 @@ static void __guc_exec_queue_process_msg_resume(struct xe_sched_msg *msg)
 
 static void guc_exec_queue_process_msg(struct xe_sched_msg *msg)
 {
+	/* PM get, ref can be zero, dma-fencing path */
+
 	trace_xe_sched_msg_recv(msg);
 
 	switch (msg->opcode) {
@@ -1186,6 +1188,8 @@ static void guc_exec_queue_process_msg(struct xe_sched_msg *msg)
 	default:
 		XE_WARN_ON("Unknown message type");
 	}
+
+	/* PM put, ref can go to zero, dma-fencing path */
 }
 
 static const struct drm_sched_backend_ops drm_sched_ops = {
diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
index de1030a47588..d2ef0a5b514e 100644
--- a/drivers/gpu/drm/xe/xe_pt.c
+++ b/drivers/gpu/drm/xe/xe_pt.c
@@ -1104,8 +1104,18 @@ static void invalidation_fence_work_func(struct work_struct *w)
 	struct invalidation_fence *ifence =
 		container_of(w, struct invalidation_fence, work);
 
+	/*
+	 * PM get, ref can be zero.
+	 *
+	 * Ideally make this so we have at least 1 ref, maybe if we take a
+	 * reference to the job this is attached and drop the ref after calling
+	 * xe_gt_tlb_invalidation_vma we can ensure the device is awake?
+	 */
+
 	trace_xe_gt_tlb_invalidation_fence_work_func(&ifence->base);
 	xe_gt_tlb_invalidation_vma(ifence->gt, &ifence->base, ifence->vma);
+
+	/* PM put, ref can go to zero */
 }
 
 static int invalidation_fence_init(struct xe_gt *gt,
-- 
2.34.1