[Mesa-dev] [PATCH 5/6] svga: also do resource readback for some map-write operations

[Brian Paul]

We previously only did a buffer readback if it was dirty and we were
about to do a read-transfer.  Now also do a readback for write-transfers
when not overwriting the entire buffer.  We have to do that to keep the
guest/host buffers synchronized in order to support host-side buffer
copies with SVGA3dCmdDXBufferCopy.

Tested with full piglit run.
---
 src/gallium/drivers/svga/svga_resource_buffer.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/src/gallium/drivers/svga/svga_resource_buffer.c b/src/gallium/drivers/svga/svga_resource_buffer.c
index 9ecb975..192425b 100644
--- a/src/gallium/drivers/svga/svga_resource_buffer.c
+++ b/src/gallium/drivers/svga/svga_resource_buffer.c
@@ -95,11 +95,16 @@ svga_buffer_transfer_map(struct pipe_context *pipe,
    transfer->usage = usage;
    transfer->box = *box;
 
-   if ((usage & PIPE_TRANSFER_READ) && sbuf->dirty) {
-      /* Only need to test for vgpu10 since only vgpu10 features (streamout,
-       * buffer copy) can modify buffers on the device.
+   if (sbuf->dirty) {
+      /* dirty means the host copy of the resource was modified, probably
+       * either with stream output or a buffer copy (only possible with vgpu10.
+       * We may need to do a readback to update the guest copy.
        */
-      if (svga_have_vgpu10(svga)) {
+      if (svga_have_vgpu10(svga) &&
+          ((usage & PIPE_TRANSFER_READ) != 0 ||
+           ((usage & PIPE_TRANSFER_WRITE) != 0 &&
+            (box->x != 0 || box->width != resource->width0)))) {
+         /* mapping for read, or writing a subset of the resource */
          enum pipe_error ret;
          assert(sbuf->handle);
          ret = SVGA3D_vgpu10_ReadbackSubResource(svga->swc, sbuf->handle, 0);
@@ -112,9 +117,9 @@ svga_buffer_transfer_map(struct pipe_context *pipe,
          svga->hud.num_readbacks++;
 
          svga_context_finish(svga);
-
-         sbuf->dirty = FALSE;
       }
+
+      sbuf->dirty = FALSE;
    }
 
    if (usage & PIPE_TRANSFER_WRITE) {
-- 
1.9.1