drm/vc4: hvs: Destroy dlist allocations immediately when running a test

When running a kunit test, the driver runs with a mock device. As such,
any attempt to read or write to a hardware register will fail the
current test immediately.

The dlist allocation management recently introduced will read the
current frame count from the HVS to defer its destruction until a
subsequent frame has been output. This obviously involves a register
read that fails the Kunit tests.

Change the destruction deferral function to destroy the allocation
immediately if we run under kunit. This is essentially harmless since
the main reason for that deferall is to prevent any access to the
hardware dlist while a frame described by that list is rendered. On our
mock driver, we have neither a hardware dlist nor a rendering, so it
doesn't matter.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>

Author: mripard

drivers/gpu/drm/vc4/vc4_hvs.c

@@ -490,6 +490,18 @@ void vc4_hvs_mark_dlist_entry_stale(struct vc4_hvs *hvs,
 	if (!drm_mm_node_allocated(&alloc->mm_node))
 		return;
 
+	/*
+	 * Kunit tests run with a mock device and we consider any hardware
+	 * access a test failure. Let's free the dlist allocation right away if
+	 * we're running under kunit, we won't risk a dlist corruption anyway.
+	 */
+	if (kunit_get_current_test()) {
+		spin_lock_irqsave(&hvs->mm_lock, flags);
+		vc4_hvs_free_dlist_entry_locked(hvs, alloc);
+		spin_unlock_irqrestore(&hvs->mm_lock, flags);
+		return;
+	}
+
 	frcnt = vc4_hvs_get_fifo_frame_count(hvs, alloc->channel);
 	alloc->target_frame_count = (frcnt + 1) & ((1 << 6) - 1);