virgl: fix readback with pending transfers

When readback is true, and there are pending writes in the transfer
queue, we should flush to avoid reading back outdated data.  This
fixes piglit arb_copy_buffer/dlist and a subtest of
arb_copy_buffer/data-sync.

Signed-off-by: Chia-I Wu <[email protected]>
Reviewed-by: Alexandros Frantzis <[email protected]>

1 files changed, 26 insertions, 6 deletions

diff --git a/src/gallium/drivers/virgl/virgl_resource.c b/src/gallium/drivers/virgl/virgl_resource.c
index 6e23687b594..8e3d6b38423 100644
--- a/src/gallium/drivers/virgl/virgl_resource.c
+++ b/src/gallium/drivers/virgl/virgl_resource.c
@@ -87,16 +87,21 @@ virgl_resource_transfer_prepare(struct virgl_context *vctx,
    if (xfer->base.usage & PIPE_TRANSFER_MAP_DIRECTLY)
       return VIRGL_TRANSFER_MAP_ERROR;
 
+   /* We break the logic down into four steps
+    *
+    * step 1: determine the required operations independently
+    * step 2: look for chances to skip the operations
+    * step 3: resolve dependencies between the operations
+    * step 4: execute the operations
+    */
+
    flush = virgl_res_needs_flush(vctx, xfer);
    readback = virgl_res_needs_readback(vctx, res, xfer->base.usage,
                                        xfer->base.level);
-
    /* We need to wait for all cmdbufs, current or previous, that access the
-    * resource to finish, unless synchronization is disabled.  Readback, which
-    * is yet another command and is transparent to the state trackers, should
-    * also be waited for.
+    * resource to finish unless synchronization is disabled.
     */
-   wait = !(xfer->base.usage & PIPE_TRANSFER_UNSYNCHRONIZED) || readback;
+   wait = !(xfer->base.usage & PIPE_TRANSFER_UNSYNCHRONIZED);
 
    /* When the transfer range consists of only uninitialized data, we can
     * assume the GPU is not accessing the range and readback is unnecessary.
@@ -111,7 +116,22 @@ virgl_resource_transfer_prepare(struct virgl_context *vctx,
       wait = false;
    }
 
-   /* XXX This is incorrect.  Consider
+   /* readback has some implications */
+   if (readback) {
+      /* Readback is yet another command and is transparent to the state
+       * trackers.  It should be waited for in all cases, including when
+       * PIPE_TRANSFER_UNSYNCHRONIZED is set.
+       */
+      wait = true;
+
+      /* When the transfer queue has pending writes to this transfer's region,
+       * we have to flush before readback.
+       */
+      if (!flush && virgl_transfer_queue_is_queued(&vctx->queue, xfer))
+         flush = true;
+   }
+
+   /* XXX This is incorrect and will be removed.  Consider
     *
     *   glTexImage2D(..., data1);
     *   glDrawArrays();