drm/vc4: Use DMA Resv to implement VC4 wait BO IOCTL

Since the BOs used by VC4 have DMA Reservation Objects attached to
them, waiting for seqnos to check BO availability is unnecessary.
Instead, `drm_gem_dma_resv_wait()` can be used.

Signed-off-by: Maíra Canal <[e-mail]>
Reviewed-by: Melissa Wen <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/vc4/vc4_gem.c

···
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 	int ret;
 	struct drm_vc4_wait_bo *args = data;
-	struct drm_gem_object *gem_obj;
-	struct vc4_bo *bo;
+	unsigned long timeout_jiffies =
+		usecs_to_jiffies(div_u64(args->timeout_ns, 1000));
+	ktime_t start = ktime_get();
+	u64 delta_ns;
 
 	if (WARN_ON_ONCE(vc4->gen > VC4_GEN_4))
 		return -ENODEV;
···
 	if (args->pad != 0)
 		return -EINVAL;
 
-	gem_obj = drm_gem_object_lookup(file_priv, args->handle);
-	if (!gem_obj) {
-		DRM_DEBUG("Failed to look up GEM BO %d\n", args->handle);
-		return -EINVAL;
-	}
-	bo = to_vc4_bo(gem_obj);
+	ret = drm_gem_dma_resv_wait(file_priv, args->handle,
+				    true, timeout_jiffies);
 
-	ret = vc4_wait_for_seqno_ioctl_helper(dev, bo->seqno,
-					      &args->timeout_ns);
+	/* Decrement the user's timeout, in case we got interrupted
+	 * such that the ioctl will be restarted.
+	 */
+	delta_ns = ktime_to_ns(ktime_sub(ktime_get(), start));
+	if (delta_ns < args->timeout_ns)
+		args->timeout_ns -= delta_ns;
+	else
+		args->timeout_ns = 0;
 
-	drm_gem_object_put(gem_obj);
 	return ret;
 }