drm/i915: Provide an i915_active.acquire callback

If we introduce a callback for i915_active that is only called the first
time we use the i915_active and is symmetrically paired with the
i915_active.retire callback, we can replace the open-coded and
non-atomic implementations -- which will be very fragile (i.e. broken)
upon removing the struct_mutex serialisation.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190621183801.23252-4-chris@chris-wilson.co.uk

1 files changed, 13 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.c b/drivers/gpu/drm/i915/gt/intel_timeline.c
index 44273b7c96f8..478258274986 100644
--- a/drivers/gpu/drm/i915/gt/intel_timeline.c
+++ b/drivers/gpu/drm/i915/gt/intel_timeline.c
@@ -146,6 +146,15 @@ static void __cacheline_retire(struct i915_active *active)
 		__idle_cacheline_free(cl);
 }
 
+static int __cacheline_active(struct i915_active *active)
+{
+	struct intel_timeline_cacheline *cl =
+		container_of(active, typeof(*cl), active);
+
+	__i915_vma_pin(cl->hwsp->vma);
+	return 0;
+}
+
 static struct intel_timeline_cacheline *
 cacheline_alloc(struct intel_timeline_hwsp *hwsp, unsigned int cacheline)
 {
@@ -168,15 +177,16 @@ cacheline_alloc(struct intel_timeline_hwsp *hwsp, unsigned int cacheline)
 	cl->hwsp = hwsp;
 	cl->vaddr = page_pack_bits(vaddr, cacheline);
 
-	i915_active_init(hwsp->gt->i915, &cl->active, __cacheline_retire);
+	i915_active_init(hwsp->gt->i915, &cl->active,
+			 __cacheline_active, __cacheline_retire);
 
 	return cl;
 }
 
 static void cacheline_acquire(struct intel_timeline_cacheline *cl)
 {
-	if (cl && i915_active_acquire(&cl->active))
-		__i915_vma_pin(cl->hwsp->vma);
+	if (cl)
+		i915_active_acquire(&cl->active);
 }
 
 static void cacheline_release(struct intel_timeline_cacheline *cl)