drm/i915: Do not share hwsp across contexts any more, v8.

Instead of sharing pages with breadcrumbs, give each timeline a
single page. This allows unrelated timelines not to share locks
any more during command submission.

As an additional benefit, seqno wraparound no longer requires
i915_vma_pin, which means we no longer need to worry about a
potential -EDEADLK at a point where we are ready to submit.

Changes since v1:
- Fix erroneous i915_vma_acquire that should be a i915_vma_release (ickle).
- Extra check for completion in intel_read_hwsp().
Changes since v2:
- Fix inconsistent indent in hwsp_alloc() (kbuild)
- memset entire cacheline to 0.
Changes since v3:
- Do same in intel_timeline_reset_seqno(), and clflush for good measure.
Changes since v4:
- Use refcounting on timeline, instead of relying on i915_active.
- Fix waiting on kernel requests.
Changes since v5:
- Bump amount of slots to maximum (256), for best wraparounds.
- Add hwsp_offset to i915_request to fix potential wraparound hang.
- Ensure timeline wrap test works with the changes.
- Assign hwsp in intel_timeline_read_hwsp() within the rcu lock to
fix a hang.
Changes since v6:
- Rename i915_request_active_offset to i915_request_active_seqno(),
and elaborate the function. (tvrtko)
Changes since v7:
- Move hunk to where it belongs. (jekstrand)
- Replace CACHELINE_BYTES with TIMELINE_SEQNO_BYTES. (jekstrand)

Signed-off-by: Maarten Lankhorst <[e-mail]>
Reviewed-by: Thomas Hellström <[e-mail]> #v1
Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/i915/gt/gen2_engine_cs.c

···
 				   int flush, int post)
 {
 	GEM_BUG_ON(i915_request_active_timeline(rq)->hwsp_ggtt != rq->engine->status_page.vma);
-	GEM_BUG_ON(offset_in_page(i915_request_active_timeline(rq)->hwsp_offset) != I915_GEM_HWS_SEQNO_ADDR);
+	GEM_BUG_ON(offset_in_page(rq->hwsp_seqno) != I915_GEM_HWS_SEQNO_ADDR);
 
 	*cs++ = MI_FLUSH;
 

drivers/gpu/drm/i915/gt/gen6_engine_cs.c

···
 		 PIPE_CONTROL_DC_FLUSH_ENABLE |
 		 PIPE_CONTROL_QW_WRITE |
 		 PIPE_CONTROL_CS_STALL);
-	*cs++ = i915_request_active_timeline(rq)->hwsp_offset |
+	*cs++ = i915_request_active_seqno(rq) |
 		PIPE_CONTROL_GLOBAL_GTT;
 	*cs++ = rq->fence.seqno;
 
···
 		 PIPE_CONTROL_QW_WRITE |
 		 PIPE_CONTROL_GLOBAL_GTT_IVB |
 		 PIPE_CONTROL_CS_STALL);
-	*cs++ = i915_request_active_timeline(rq)->hwsp_offset;
+	*cs++ = i915_request_active_seqno(rq);
 	*cs++ = rq->fence.seqno;
 
 	*cs++ = MI_USER_INTERRUPT;
···
 u32 *gen6_emit_breadcrumb_xcs(struct i915_request *rq, u32 *cs)
 {
 	GEM_BUG_ON(i915_request_active_timeline(rq)->hwsp_ggtt != rq->engine->status_page.vma);
-	GEM_BUG_ON(offset_in_page(i915_request_active_timeline(rq)->hwsp_offset) != I915_GEM_HWS_SEQNO_ADDR);
+	GEM_BUG_ON(offset_in_page(rq->hwsp_seqno) != I915_GEM_HWS_SEQNO_ADDR);
 
 	*cs++ = MI_FLUSH_DW | MI_FLUSH_DW_OP_STOREDW | MI_FLUSH_DW_STORE_INDEX;
 	*cs++ = I915_GEM_HWS_SEQNO_ADDR | MI_FLUSH_DW_USE_GTT;
···
 	int i;
 
 	GEM_BUG_ON(i915_request_active_timeline(rq)->hwsp_ggtt != rq->engine->status_page.vma);
-	GEM_BUG_ON(offset_in_page(i915_request_active_timeline(rq)->hwsp_offset) != I915_GEM_HWS_SEQNO_ADDR);
+	GEM_BUG_ON(offset_in_page(rq->hwsp_seqno) != I915_GEM_HWS_SEQNO_ADDR);
 
 	*cs++ = MI_FLUSH_DW | MI_INVALIDATE_TLB |
 		MI_FLUSH_DW_OP_STOREDW | MI_FLUSH_DW_STORE_INDEX;

drivers/gpu/drm/i915/gt/gen8_engine_cs.c

···
 
 static u32 hwsp_offset(const struct i915_request *rq)
 {
-	const struct intel_timeline_cacheline *cl;
+	const struct intel_timeline *tl;
 
-	/* Before the request is executed, the timeline/cachline is fixed */
+	/* Before the request is executed, the timeline is fixed */
+	tl = rcu_dereference_protected(rq->timeline,
+				       !i915_request_signaled(rq));
 
-	cl = rcu_dereference_protected(rq->hwsp_cacheline, 1);
-	if (cl)
-		return cl->ggtt_offset;
-
-	return rcu_dereference_protected(rq->timeline, 1)->hwsp_offset;
+	/* See the comment in i915_request_active_seqno(). */
+	return page_mask_bits(tl->hwsp_offset) + offset_in_page(rq->hwsp_seqno);
 }
 
 int gen8_emit_init_breadcrumb(struct i915_request *rq)

drivers/gpu/drm/i915/gt/intel_engine_cs.c

···
 	frame->rq.engine = engine;
 	frame->rq.context = ce;
 	rcu_assign_pointer(frame->rq.timeline, ce->timeline);
+	frame->rq.hwsp_seqno = ce->timeline->hwsp_seqno;
 
 	frame->ring.vaddr = frame->cs;
 	frame->ring.size = sizeof(frame->cs);

drivers/gpu/drm/i915/gt/intel_gt_types.h

···
 	struct intel_gt_timelines {
 		spinlock_t lock; /* protects active_list */
 		struct list_head active_list;
-
-		/* Pack multiple timelines' seqnos into the same page */
-		spinlock_t hwsp_lock;
-		struct list_head hwsp_free_list;
 	} timelines;
 
 	struct intel_gt_requests {

drivers/gpu/drm/i915/gt/intel_timeline.c

···
 #include "intel_ring.h"
 #include "intel_timeline.h"
 
-#define ptr_set_bit(ptr, bit) ((typeof(ptr))((unsigned long)(ptr) | BIT(bit)))
-#define ptr_test_bit(ptr, bit) ((unsigned long)(ptr) & BIT(bit))
+#define TIMELINE_SEQNO_BYTES 8
 
-#define CACHELINE_BITS 6
-#define CACHELINE_FREE CACHELINE_BITS
-
-struct intel_timeline_hwsp {
-	struct intel_gt *gt;
-	struct intel_gt_timelines *gt_timelines;
-	struct list_head free_link;
-	struct i915_vma *vma;
-	u64 free_bitmap;
-};
-
-static struct i915_vma *__hwsp_alloc(struct intel_gt *gt)
+static struct i915_vma *hwsp_alloc(struct intel_gt *gt)
 {
 	struct drm_i915_private *i915 = gt->i915;
 	struct drm_i915_gem_object *obj;
···
 	return vma;
 }
 
-static struct i915_vma *
-hwsp_alloc(struct intel_timeline *timeline, unsigned int *cacheline)
-{
-	struct intel_gt_timelines *gt = &timeline->gt->timelines;
-	struct intel_timeline_hwsp *hwsp;
-
-	BUILD_BUG_ON(BITS_PER_TYPE(u64) * CACHELINE_BYTES > PAGE_SIZE);
-
-	spin_lock_irq(&gt->hwsp_lock);
-
-	/* hwsp_free_list only contains HWSP that have available cachelines */
-	hwsp = list_first_entry_or_null(&gt->hwsp_free_list,
-					typeof(*hwsp), free_link);
-	if (!hwsp) {
-		struct i915_vma *vma;
-
-		spin_unlock_irq(&gt->hwsp_lock);
-
-		hwsp = kmalloc(sizeof(*hwsp), GFP_KERNEL);
-		if (!hwsp)
-			return ERR_PTR(-ENOMEM);
-
-		vma = __hwsp_alloc(timeline->gt);
-		if (IS_ERR(vma)) {
-			kfree(hwsp);
-			return vma;
-		}
-
-		GT_TRACE(timeline->gt, "new HWSP allocated\n");
-
-		vma->private = hwsp;
-		hwsp->gt = timeline->gt;
-		hwsp->vma = vma;
-		hwsp->free_bitmap = ~0ull;
-		hwsp->gt_timelines = gt;
-
-		spin_lock_irq(&gt->hwsp_lock);
-		list_add(&hwsp->free_link, &gt->hwsp_free_list);
-	}
-
-	GEM_BUG_ON(!hwsp->free_bitmap);
-	*cacheline = __ffs64(hwsp->free_bitmap);
-	hwsp->free_bitmap &= ~BIT_ULL(*cacheline);
-	if (!hwsp->free_bitmap)
-		list_del(&hwsp->free_link);
-
-	spin_unlock_irq(&gt->hwsp_lock);
-
-	GEM_BUG_ON(hwsp->vma->private != hwsp);
-	return hwsp->vma;
-}
-
-static void __idle_hwsp_free(struct intel_timeline_hwsp *hwsp, int cacheline)
-{
-	struct intel_gt_timelines *gt = hwsp->gt_timelines;
-	unsigned long flags;
-
-	spin_lock_irqsave(&gt->hwsp_lock, flags);
-
-	/* As a cacheline becomes available, publish the HWSP on the freelist */
-	if (!hwsp->free_bitmap)
-		list_add_tail(&hwsp->free_link, &gt->hwsp_free_list);
-
-	GEM_BUG_ON(cacheline >= BITS_PER_TYPE(hwsp->free_bitmap));
-	hwsp->free_bitmap |= BIT_ULL(cacheline);
-
-	/* And if no one is left using it, give the page back to the system */
-	if (hwsp->free_bitmap == ~0ull) {
-		i915_vma_put(hwsp->vma);
-		list_del(&hwsp->free_link);
-		kfree(hwsp);
-	}
-
-	spin_unlock_irqrestore(&gt->hwsp_lock, flags);
-}
-
-static void __rcu_cacheline_free(struct rcu_head *rcu)
-{
-	struct intel_timeline_cacheline *cl =
-		container_of(rcu, typeof(*cl), rcu);
-
-	/* Must wait until after all *rq->hwsp are complete before removing */
-	i915_gem_object_unpin_map(cl->hwsp->vma->obj);
-	__idle_hwsp_free(cl->hwsp, ptr_unmask_bits(cl->vaddr, CACHELINE_BITS));
-
-	i915_active_fini(&cl->active);
-	kfree(cl);
-}
-
-static void __idle_cacheline_free(struct intel_timeline_cacheline *cl)
-{
-	GEM_BUG_ON(!i915_active_is_idle(&cl->active));
-	call_rcu(&cl->rcu, __rcu_cacheline_free);
-}
-
 __i915_active_call
-static void __cacheline_retire(struct i915_active *active)
+static void __timeline_retire(struct i915_active *active)
 {
-	struct intel_timeline_cacheline *cl =
-		container_of(active, typeof(*cl), active);
+	struct intel_timeline *tl =
+		container_of(active, typeof(*tl), active);
 
-	i915_vma_unpin(cl->hwsp->vma);
-	if (ptr_test_bit(cl->vaddr, CACHELINE_FREE))
-		__idle_cacheline_free(cl);
+	i915_vma_unpin(tl->hwsp_ggtt);
+	intel_timeline_put(tl);
 }
 
-static int __cacheline_active(struct i915_active *active)
+static int __timeline_active(struct i915_active *active)
 {
-	struct intel_timeline_cacheline *cl =
-		container_of(active, typeof(*cl), active);
+	struct intel_timeline *tl =
+		container_of(active, typeof(*tl), active);
 
-	__i915_vma_pin(cl->hwsp->vma);
+	__i915_vma_pin(tl->hwsp_ggtt);
+	intel_timeline_get(tl);
 	return 0;
-}
-
-static struct intel_timeline_cacheline *
-cacheline_alloc(struct intel_timeline_hwsp *hwsp, unsigned int cacheline)
-{
-	struct intel_timeline_cacheline *cl;
-	void *vaddr;
-
-	GEM_BUG_ON(cacheline >= BIT(CACHELINE_BITS));
-
-	cl = kmalloc(sizeof(*cl), GFP_KERNEL);
-	if (!cl)
-		return ERR_PTR(-ENOMEM);
-
-	vaddr = i915_gem_object_pin_map(hwsp->vma->obj, I915_MAP_WB);
-	if (IS_ERR(vaddr)) {
-		kfree(cl);
-		return ERR_CAST(vaddr);
-	}
-
-	cl->hwsp = hwsp;
-	cl->vaddr = page_pack_bits(vaddr, cacheline);
-
-	i915_active_init(&cl->active, __cacheline_active, __cacheline_retire);
-
-	return cl;
-}
-
-static void cacheline_acquire(struct intel_timeline_cacheline *cl,
-			      u32 ggtt_offset)
-{
-	if (!cl)
-		return;
-
-	cl->ggtt_offset = ggtt_offset;
-	i915_active_acquire(&cl->active);
-}
-
-static void cacheline_release(struct intel_timeline_cacheline *cl)
-{
-	if (cl)
-		i915_active_release(&cl->active);
-}
-
-static void cacheline_free(struct intel_timeline_cacheline *cl)
-{
-	if (!i915_active_acquire_if_busy(&cl->active)) {
-		__idle_cacheline_free(cl);
-		return;
-	}
-
-	GEM_BUG_ON(ptr_test_bit(cl->vaddr, CACHELINE_FREE));
-	cl->vaddr = ptr_set_bit(cl->vaddr, CACHELINE_FREE);
-
-	i915_active_release(&cl->active);
 }
 
 static int intel_timeline_init(struct intel_timeline *timeline,
···
 			       unsigned int offset)
 {
 	void *vaddr;
+	u32 *seqno;
 
 	kref_init(&timeline->kref);
 	atomic_set(&timeline->pin_count, 0);
 
 	timeline->gt = gt;
 
-	timeline->has_initial_breadcrumb = !hwsp;
-	timeline->hwsp_cacheline = NULL;
-
-	if (!hwsp) {
-		struct intel_timeline_cacheline *cl;
-		unsigned int cacheline;
-
-		hwsp = hwsp_alloc(timeline, &cacheline);
+	if (hwsp) {
+		timeline->hwsp_offset = offset;
+		timeline->hwsp_ggtt = i915_vma_get(hwsp);
+	} else {
+		timeline->has_initial_breadcrumb = true;
+		hwsp = hwsp_alloc(gt);
 		if (IS_ERR(hwsp))
 			return PTR_ERR(hwsp);
-
-		cl = cacheline_alloc(hwsp->private, cacheline);
-		if (IS_ERR(cl)) {
-			__idle_hwsp_free(hwsp->private, cacheline);
-			return PTR_ERR(cl);
-		}
-
-		timeline->hwsp_cacheline = cl;
-		timeline->hwsp_offset = cacheline * CACHELINE_BYTES;
-
-		vaddr = page_mask_bits(cl->vaddr);
-	} else {
-		timeline->hwsp_offset = offset;
-		vaddr = i915_gem_object_pin_map(hwsp->obj, I915_MAP_WB);
-		if (IS_ERR(vaddr))
-			return PTR_ERR(vaddr);
+		timeline->hwsp_ggtt = hwsp;
 	}
 
-	timeline->hwsp_seqno =
-		memset(vaddr + timeline->hwsp_offset, 0, CACHELINE_BYTES);
+	vaddr = i915_gem_object_pin_map(hwsp->obj, I915_MAP_WB);
+	if (IS_ERR(vaddr))
+		return PTR_ERR(vaddr);
 
-	timeline->hwsp_ggtt = i915_vma_get(hwsp);
+	timeline->hwsp_map = vaddr;
+	seqno = vaddr + timeline->hwsp_offset;
+	WRITE_ONCE(*seqno, 0);
+	timeline->hwsp_seqno = seqno;
+
 	GEM_BUG_ON(timeline->hwsp_offset >= hwsp->size);
 
 	timeline->fence_context = dma_fence_context_alloc(1);
···
 	INIT_LIST_HEAD(&timeline->requests);
 
 	i915_syncmap_init(&timeline->sync);
+	i915_active_init(&timeline->active, __timeline_active, __timeline_retire);
 
 	return 0;
 }
···
 
 	spin_lock_init(&timelines->lock);
 	INIT_LIST_HEAD(&timelines->active_list);
-
-	spin_lock_init(&timelines->hwsp_lock);
-	INIT_LIST_HEAD(&timelines->hwsp_free_list);
 }
 
-static void intel_timeline_fini(struct intel_timeline *timeline)
+static void intel_timeline_fini(struct rcu_head *rcu)
 {
-	GEM_BUG_ON(atomic_read(&timeline->pin_count));
-	GEM_BUG_ON(!list_empty(&timeline->requests));
-	GEM_BUG_ON(timeline->retire);
+	struct intel_timeline *timeline =
+		container_of(rcu, struct intel_timeline, rcu);
 
-	if (timeline->hwsp_cacheline)
-		cacheline_free(timeline->hwsp_cacheline);
-	else
-		i915_gem_object_unpin_map(timeline->hwsp_ggtt->obj);
+	i915_gem_object_unpin_map(timeline->hwsp_ggtt->obj);
 
 	i915_vma_put(timeline->hwsp_ggtt);
+	i915_active_fini(&timeline->active);
+	kfree(timeline);
 }
 
 struct intel_timeline *
···
 	GT_TRACE(tl->gt, "timeline:%llx using HWSP offset:%x\n",
 		 tl->fence_context, tl->hwsp_offset);
 
-	cacheline_acquire(tl->hwsp_cacheline, tl->hwsp_offset);
+	i915_active_acquire(&tl->active);
 	if (atomic_fetch_inc(&tl->pin_count)) {
-		cacheline_release(tl->hwsp_cacheline);
+		i915_active_release(&tl->active);
 		__i915_vma_unpin(tl->hwsp_ggtt);
 	}
 
···
 
 void intel_timeline_reset_seqno(const struct intel_timeline *tl)
 {
+	u32 *hwsp_seqno = (u32 *)tl->hwsp_seqno;
 	/* Must be pinned to be writable, and no requests in flight. */
 	GEM_BUG_ON(!atomic_read(&tl->pin_count));
-	WRITE_ONCE(*(u32 *)tl->hwsp_seqno, tl->seqno);
+
+	memset(hwsp_seqno + 1, 0, TIMELINE_SEQNO_BYTES - sizeof(*hwsp_seqno));
+	WRITE_ONCE(*hwsp_seqno, tl->seqno);
+	clflush(hwsp_seqno);
 }
 
 void intel_timeline_enter(struct intel_timeline *tl)
···
 	return tl->seqno += 1 + tl->has_initial_breadcrumb;
 }
 
-static void timeline_rollback(struct intel_timeline *tl)
-{
-	tl->seqno -= 1 + tl->has_initial_breadcrumb;
-}
-
 static noinline int
 __intel_timeline_get_seqno(struct intel_timeline *tl,
-			   struct i915_request *rq,
 			   u32 *seqno)
 {
-	struct intel_timeline_cacheline *cl;
-	unsigned int cacheline;
-	struct i915_vma *vma;
-	void *vaddr;
-	int err;
+	u32 next_ofs = offset_in_page(tl->hwsp_offset + TIMELINE_SEQNO_BYTES);
 
-	might_lock(&tl->gt->ggtt->vm.mutex);
-	GT_TRACE(tl->gt, "timeline:%llx wrapped\n", tl->fence_context);
+	/* w/a: bit 5 needs to be zero for MI_FLUSH_DW address. */
+	if (TIMELINE_SEQNO_BYTES <= BIT(5) && (next_ofs & BIT(5)))
+		next_ofs = offset_in_page(next_ofs + BIT(5));
 
-	/*
-	 * If there is an outstanding GPU reference to this cacheline,
-	 * such as it being sampled by a HW semaphore on another timeline,
-	 * we cannot wraparound our seqno value (the HW semaphore does
-	 * a strict greater-than-or-equals compare, not i915_seqno_passed).
-	 * So if the cacheline is still busy, we must detach ourselves
-	 * from it and leave it inflight alongside its users.
-	 *
-	 * However, if nobody is watching and we can guarantee that nobody
-	 * will, we could simply reuse the same cacheline.
-	 *
-	 * if (i915_active_request_is_signaled(&tl->last_request) &&
-	 *     i915_active_is_signaled(&tl->hwsp_cacheline->active))
-	 *	return 0;
-	 *
-	 * That seems unlikely for a busy timeline that needed to wrap in
-	 * the first place, so just replace the cacheline.
-	 */
-
-	vma = hwsp_alloc(tl, &cacheline);
-	if (IS_ERR(vma)) {
-		err = PTR_ERR(vma);
-		goto err_rollback;
-	}
-
-	err = i915_ggtt_pin(vma, NULL, 0, PIN_HIGH);
-	if (err) {
-		__idle_hwsp_free(vma->private, cacheline);
-		goto err_rollback;
-	}
-
-	cl = cacheline_alloc(vma->private, cacheline);
-	if (IS_ERR(cl)) {
-		err = PTR_ERR(cl);
-		__idle_hwsp_free(vma->private, cacheline);
-		goto err_unpin;
-	}
-	GEM_BUG_ON(cl->hwsp->vma != vma);
-
-	/*
-	 * Attach the old cacheline to the current request, so that we only
-	 * free it after the current request is retired, which ensures that
-	 * all writes into the cacheline from previous requests are complete.
-	 */
-	err = i915_active_ref(&tl->hwsp_cacheline->active,
-			      tl->fence_context,
-			      &rq->fence);
-	if (err)
-		goto err_cacheline;
-
-	cacheline_release(tl->hwsp_cacheline); /* ownership now xfered to rq */
-	cacheline_free(tl->hwsp_cacheline);
-
-	i915_vma_unpin(tl->hwsp_ggtt); /* binding kept alive by old cacheline */
-	i915_vma_put(tl->hwsp_ggtt);
-
-	tl->hwsp_ggtt = i915_vma_get(vma);
-
-	vaddr = page_mask_bits(cl->vaddr);
-	tl->hwsp_offset = cacheline * CACHELINE_BYTES;
-	tl->hwsp_seqno =
-		memset(vaddr + tl->hwsp_offset, 0, CACHELINE_BYTES);
-
-	tl->hwsp_offset += i915_ggtt_offset(vma);
-	GT_TRACE(tl->gt, "timeline:%llx using HWSP offset:%x\n",
-		 tl->fence_context, tl->hwsp_offset);
-
-	cacheline_acquire(cl, tl->hwsp_offset);
-	tl->hwsp_cacheline = cl;
+	tl->hwsp_offset = i915_ggtt_offset(tl->hwsp_ggtt) + next_ofs;
+	tl->hwsp_seqno = tl->hwsp_map + next_ofs;
+	intel_timeline_reset_seqno(tl);
 
 	*seqno = timeline_advance(tl);
 	GEM_BUG_ON(i915_seqno_passed(*tl->hwsp_seqno, *seqno));
 	return 0;
-
-err_cacheline:
-	cacheline_free(cl);
-err_unpin:
-	i915_vma_unpin(vma);
-err_rollback:
-	timeline_rollback(tl);
-	return err;
 }
 
 int intel_timeline_get_seqno(struct intel_timeline *tl,
···
 	*seqno = timeline_advance(tl);
 
 	/* Replace the HWSP on wraparound for HW semaphores */
-	if (unlikely(!*seqno && tl->hwsp_cacheline))
-		return __intel_timeline_get_seqno(tl, rq, seqno);
+	if (unlikely(!*seqno && tl->has_initial_breadcrumb))
+		return __intel_timeline_get_seqno(tl, seqno);
 
 	return 0;
-}
-
-static int cacheline_ref(struct intel_timeline_cacheline *cl,
-			 struct i915_request *rq)
-{
-	return i915_active_add_request(&cl->active, rq);
 }
 
 int intel_timeline_read_hwsp(struct i915_request *from,
 			     struct i915_request *to,
 			     u32 *hwsp)
 {
-	struct intel_timeline_cacheline *cl;
+	struct intel_timeline *tl;
 	int err;
 
-	GEM_BUG_ON(!rcu_access_pointer(from->hwsp_cacheline));
-
 	rcu_read_lock();
-	cl = rcu_dereference(from->hwsp_cacheline);
-	if (i915_request_signaled(from)) /* confirm cacheline is valid */
-		goto unlock;
-	if (unlikely(!i915_active_acquire_if_busy(&cl->active)))
-		goto unlock; /* seqno wrapped and completed! */
-	if (unlikely(__i915_request_is_complete(from)))
-		goto release;
+	tl = rcu_dereference(from->timeline);
+	if (i915_request_signaled(from) ||
+	    !i915_active_acquire_if_busy(&tl->active))
+		tl = NULL;
+
+	if (tl) {
+		/* hwsp_offset may wraparound, so use from->hwsp_seqno */
+		*hwsp = i915_ggtt_offset(tl->hwsp_ggtt) +
+			offset_in_page(from->hwsp_seqno);
+	}
+
+	/* ensure we wait on the right request, if not, we completed */
+	if (tl && __i915_request_is_complete(from)) {
+		i915_active_release(&tl->active);
+		tl = NULL;
+	}
 	rcu_read_unlock();
 
-	err = cacheline_ref(cl, to);
-	if (err)
+	if (!tl)
+		return 1;
+
+	/* Can't do semaphore waits on kernel context */
+	if (!tl->has_initial_breadcrumb) {
+		err = -EINVAL;
 		goto out;
+	}
 
-	*hwsp = cl->ggtt_offset;
+	err = i915_active_add_request(&tl->active, to);
+
 out:
-	i915_active_release(&cl->active);
+	i915_active_release(&tl->active);
 	return err;
-
-release:
-	i915_active_release(&cl->active);
-unlock:
-	rcu_read_unlock();
-	return 1;
 }
 
 void intel_timeline_unpin(struct intel_timeline *tl)
···
 	if (!atomic_dec_and_test(&tl->pin_count))
 		return;
 
-	cacheline_release(tl->hwsp_cacheline);
-
+	i915_active_release(&tl->active);
 	__i915_vma_unpin(tl->hwsp_ggtt);
 }
 
···
 	struct intel_timeline *timeline =
 		container_of(kref, typeof(*timeline), kref);
 
-	intel_timeline_fini(timeline);
-	kfree_rcu(timeline, rcu);
+	GEM_BUG_ON(atomic_read(&timeline->pin_count));
+	GEM_BUG_ON(!list_empty(&timeline->requests));
+	GEM_BUG_ON(timeline->retire);
+
+	call_rcu(&timeline->rcu, intel_timeline_fini);
 }
 
 void intel_gt_fini_timelines(struct intel_gt *gt)
···
 	struct intel_gt_timelines *timelines = &gt->timelines;
 
 	GEM_BUG_ON(!list_empty(&timelines->active_list));
-	GEM_BUG_ON(!list_empty(&timelines->hwsp_free_list));
 }
 
 void intel_gt_show_timelines(struct intel_gt *gt,

drivers/gpu/drm/i915/gt/intel_timeline_types.h

···
 struct i915_vma;
 struct i915_syncmap;
 struct intel_gt;
-struct intel_timeline_hwsp;
 
 struct intel_timeline {
 	u64 fence_context;
···
 	atomic_t pin_count;
 	atomic_t active_count;
 
+	void *hwsp_map;
 	const u32 *hwsp_seqno;
 	struct i915_vma *hwsp_ggtt;
 	u32 hwsp_offset;
-
-	struct intel_timeline_cacheline *hwsp_cacheline;
 
 	bool has_initial_breadcrumb;
 
···
 	 * protection themselves (cf the i915_active_fence API).
 	 */
 	struct i915_active_fence last_request;
+
+	struct i915_active active;
 
 	/** A chain of completed timelines ready for early retirement. */
 	struct intel_timeline *retire;
···
 	struct list_head engine_link;
 
 	struct kref kref;
-	struct rcu_head rcu;
-};
-
-struct intel_timeline_cacheline {
-	struct i915_active active;
-
-	struct intel_timeline_hwsp *hwsp;
-	void *vaddr;
-
-	u32 ggtt_offset;
-
 	struct rcu_head rcu;
 };
 

drivers/gpu/drm/i915/gt/selftest_engine_cs.c

···
 
 static int write_timestamp(struct i915_request *rq, int slot)
 {
+	struct intel_timeline *tl =
+		rcu_dereference_protected(rq->timeline,
+					  !i915_request_signaled(rq));
 	u32 cmd;
 	u32 *cs;
 
···
 		cmd++;
 	*cs++ = cmd;
 	*cs++ = i915_mmio_reg_offset(RING_TIMESTAMP(rq->engine->mmio_base));
-	*cs++ = i915_request_timeline(rq)->hwsp_offset + slot * sizeof(u32);
+	*cs++ = tl->hwsp_offset + slot * sizeof(u32);
 	*cs++ = 0;
 
 	intel_ring_advance(rq, cs);

drivers/gpu/drm/i915/gt/selftest_timeline.c

···
 {
 	unsigned long address = (unsigned long)page_address(hwsp_page(tl));
 
-	return (address + tl->hwsp_offset) / CACHELINE_BYTES;
+	return (address + offset_in_page(tl->hwsp_offset)) / TIMELINE_SEQNO_BYTES;
 }
 
-#define CACHELINES_PER_PAGE (PAGE_SIZE / CACHELINE_BYTES)
+/* Only half of seqno's are usable, see __intel_timeline_get_seqno() */
+#define CACHELINES_PER_PAGE (PAGE_SIZE / TIMELINE_SEQNO_BYTES / 2)
 
 struct mock_hwsp_freelist {
 	struct intel_gt *gt;
···
 	if (IS_ERR(tl))
 		return PTR_ERR(tl);
 
-	if (!tl->has_initial_breadcrumb || !tl->hwsp_cacheline)
+	if (!tl->has_initial_breadcrumb)
 		goto out_free;
 
 	err = intel_timeline_pin(tl, NULL);
···
 	return 0;
 }
 
+static void switch_tl_lock(struct i915_request *from, struct i915_request *to)
+{
+	/* some light mutex juggling required; think co-routines */
+
+	if (from) {
+		lockdep_unpin_lock(&from->context->timeline->mutex, from->cookie);
+		mutex_unlock(&from->context->timeline->mutex);
+	}
+
+	if (to) {
+		mutex_lock(&to->context->timeline->mutex);
+		to->cookie = lockdep_pin_lock(&to->context->timeline->mutex);
+	}
+}
+
 static int create_watcher(struct hwsp_watcher *w,
 			  struct intel_engine_cs *engine,
 			  int ringsz)
 {
 	struct intel_context *ce;
-	struct intel_timeline *tl;
 
 	ce = intel_context_create(engine);
 	if (IS_ERR(ce))
···
 		return PTR_ERR(w->rq);
 
 	w->addr = i915_ggtt_offset(w->vma);
-	tl = w->rq->context->timeline;
 
-	/* some light mutex juggling required; think co-routines */
-	lockdep_unpin_lock(&tl->mutex, w->rq->cookie);
-	mutex_unlock(&tl->mutex);
+	switch_tl_lock(w->rq, NULL);
 
 	return 0;
 }
···
 			 bool (*op)(u32 hwsp, u32 seqno))
 {
 	struct i915_request *rq = fetch_and_zero(&w->rq);
-	struct intel_timeline *tl = rq->context->timeline;
 	u32 offset, end;
 	int err;
 
 	GEM_BUG_ON(w->addr - i915_ggtt_offset(w->vma) > w->vma->size);
 
 	i915_request_get(rq);
-	mutex_lock(&tl->mutex);
-	rq->cookie = lockdep_pin_lock(&tl->mutex);
+	switch_tl_lock(NULL, rq);
 	i915_request_add(rq);
 
 	if (i915_request_wait(rq, 0, HZ) < 0) {
···
 static void cleanup_watcher(struct hwsp_watcher *w)
 {
 	if (w->rq) {
-		struct intel_timeline *tl = w->rq->context->timeline;
-
-		mutex_lock(&tl->mutex);
-		w->rq->cookie = lockdep_pin_lock(&tl->mutex);
+		switch_tl_lock(NULL, w->rq);
 
 		i915_request_add(w->rq);
 	}
···
 	}
 
 	i915_request_put(rq);
-	rq = intel_context_create_request(ce);
+	rq = i915_request_create(ce);
 	if (IS_ERR(rq))
 		return rq;
 
···
 	if (IS_ERR(tl))
 		return PTR_ERR(tl);
 
-	if (!tl->hwsp_cacheline)
+	if (!tl->has_initial_breadcrumb)
 		goto out_free;
 
 	for (i = 0; i < ARRAY_SIZE(watcher); i++) {
···
 		do {
 			struct i915_sw_fence *submit;
 			struct i915_request *rq;
-			u32 hwsp;
+			u32 hwsp, dummy;
 
 			submit = heap_fence_create(GFP_KERNEL);
 			if (!submit) {
···
 				goto out;
 			}
 
-			/* Skip to the end, saving 30 minutes of nops */
-			tl->seqno = -10u + 2 * (count & 3);
-			WRITE_ONCE(*(u32 *)tl->hwsp_seqno, tl->seqno);
 			ce->timeline = intel_timeline_get(tl);
 
-			rq = intel_context_create_request(ce);
+			/* Ensure timeline is mapped, done during first pin */
+			err = intel_context_pin(ce);
+			if (err) {
+				intel_context_put(ce);
+				goto out;
+			}
+
+			/*
+			 * Start at a new wrap, and set seqno right before another wrap,
+			 * saving 30 minutes of nops
+			 */
+			tl->seqno = -12u + 2 * (count & 3);
+			__intel_timeline_get_seqno(tl, &dummy);
+
+			rq = i915_request_create(ce);
 			if (IS_ERR(rq)) {
 				err = PTR_ERR(rq);
+				intel_context_unpin(ce);
 				intel_context_put(ce);
 				goto out;
 			}
···
 							    GFP_KERNEL);
 			if (err < 0) {
 				i915_request_add(rq);
+				intel_context_unpin(ce);
 				intel_context_put(ce);
 				goto out;
 			}
 
-			mutex_lock(&watcher[0].rq->context->timeline->mutex);
+			switch_tl_lock(rq, watcher[0].rq);
 			err = intel_timeline_read_hwsp(rq, watcher[0].rq, &hwsp);
 			if (err == 0)
 				err = emit_read_hwsp(watcher[0].rq, /* before */
 						     rq->fence.seqno, hwsp,
 						     &watcher[0].addr);
-			mutex_unlock(&watcher[0].rq->context->timeline->mutex);
+			switch_tl_lock(watcher[0].rq, rq);
 			if (err) {
 				i915_request_add(rq);
+				intel_context_unpin(ce);
 				intel_context_put(ce);
 				goto out;
 			}
 
-			mutex_lock(&watcher[1].rq->context->timeline->mutex);
+			switch_tl_lock(rq, watcher[1].rq);
 			err = intel_timeline_read_hwsp(rq, watcher[1].rq, &hwsp);
 			if (err == 0)
 				err = emit_read_hwsp(watcher[1].rq, /* after */
 						     rq->fence.seqno, hwsp,
 						     &watcher[1].addr);
-			mutex_unlock(&watcher[1].rq->context->timeline->mutex);
+			switch_tl_lock(watcher[1].rq, rq);
 			if (err) {
 				i915_request_add(rq);
+				intel_context_unpin(ce);
 				intel_context_put(ce);
 				goto out;
 			}
···
 			i915_request_add(rq);
 
 			rq = wrap_timeline(rq);
+			intel_context_unpin(ce);
 			intel_context_put(ce);
 			if (IS_ERR(rq)) {
 				err = PTR_ERR(rq);
···
 			    3 * watcher[1].rq->ring->size)
 				break;
 
-		} while (!__igt_timeout(end_time, NULL));
-		WRITE_ONCE(*(u32 *)tl->hwsp_seqno, 0xdeadbeef);
+		} while (!__igt_timeout(end_time, NULL) &&
+			 count < (PAGE_SIZE / TIMELINE_SEQNO_BYTES - 1) / 2);
 
 		pr_info("%s: simulated %lu wraps\n", engine->name, count);
 		err = check_watcher(&watcher[1], "after", cmp_gte);
···
 		}
 
 		GEM_BUG_ON(i915_active_fence_isset(&tl->last_request));
-		tl->seqno = 0;
-		timeline_rollback(tl);
-		timeline_rollback(tl);
+		tl->seqno = -2u;
 		WRITE_ONCE(*(u32 *)tl->hwsp_seqno, tl->seqno);
 
 		for (i = 0; i < ARRAY_SIZE(rq); i++) {
···
 			goto out;
 
 		tl = ce->timeline;
-		if (!tl->has_initial_breadcrumb || !tl->hwsp_cacheline)
+		if (!tl->has_initial_breadcrumb)
 			goto out;
 
-		timeline_rollback(tl);
-		timeline_rollback(tl);
+		tl->seqno = -4u;
 		WRITE_ONCE(*(u32 *)tl->hwsp_seqno, tl->seqno);
 
 		for (i = 0; i < ARRAY_SIZE(rq); i++) {

drivers/gpu/drm/i915/i915_request.c

···
 	rq->fence.seqno = seqno;
 
 	RCU_INIT_POINTER(rq->timeline, tl);
-	RCU_INIT_POINTER(rq->hwsp_cacheline, tl->hwsp_cacheline);
 	rq->hwsp_seqno = tl->hwsp_seqno;
 	GEM_BUG_ON(__i915_request_is_complete(rq));
 
···
 		goto await_fence;
 
 	if (i915_request_has_initial_breadcrumb(to))
-		goto await_fence;
-
-	if (!rcu_access_pointer(from->hwsp_cacheline))
 		goto await_fence;
 
 	/*

drivers/gpu/drm/i915/i915_request.h

···
 	 */
 	const u32 *hwsp_seqno;
 
-	/*
-	 * If we need to access the timeline's seqno for this request in
-	 * another request, we need to keep a read reference to this associated
-	 * cacheline, so that we do not free and recycle it before the foreign
-	 * observers have completed. Hence, we keep a pointer to the cacheline
-	 * inside the timeline's HWSP vma, but it is only valid while this
-	 * request has not completed and guarded by the timeline mutex.
-	 */
-	struct intel_timeline_cacheline __rcu *hwsp_cacheline;
-
 	/** Position in the ring of the start of the request */
 	u32 head;
 
···
 	 */
 	return rcu_dereference_protected(rq->timeline,
 					 lockdep_is_held(&rq->engine->active.lock));
+}
+
+static inline u32
+i915_request_active_seqno(const struct i915_request *rq)
+{
+	u32 hwsp_phys_base =
+		page_mask_bits(i915_request_active_timeline(rq)->hwsp_offset);
+	u32 hwsp_relative_offset = offset_in_page(rq->hwsp_seqno);
+
+	/*
+	 * Because of wraparound, we cannot simply take tl->hwsp_offset,
+	 * but instead use the fact that the relative for vaddr is the
+	 * offset as for hwsp_offset. Take the top bits from tl->hwsp_offset
+	 * and combine them with the relative offset in rq->hwsp_seqno.
+	 *
+	 * As rw->hwsp_seqno is rewritten when signaled, this only works
+	 * when the request isn't signaled yet, but at that point you
+	 * no longer need the offset.
+	 */
+
+	return hwsp_phys_base + hwsp_relative_offset;
 }
 
 #endif /* I915_REQUEST_H */