[PATCH 2/2] hw/display/vmware_vga: do not discard screen updates

[Carwyn Ellis <carwynellis@gmail.com>]

In certain circumstances, typically when there is lots changing on the
screen, updates will be discarded resulting in garbled output.

This change simplifies the traversal of the display update FIFO queue
when applying updates. We just track the queue length and iterate up to
the end of the queue.

Additionanlly when adding updates to the queue, if the buffer reaches
capacity we force a flush before accepting further events.

Signed-off-by: Carwyn Ellis <carwynellis@gmail.com>
---
 hw/display/trace-events |  1 +
 hw/display/vmware_vga.c | 41 +++++++++++++++++++++++------------------
 2 files changed, 24 insertions(+), 18 deletions(-)

diff --git a/hw/display/trace-events b/hw/display/trace-events
index e1a0d2a88a..5e3cdb3fa3 100644
--- a/hw/display/trace-events
+++ b/hw/display/trace-events
@@ -24,6 +24,7 @@ vmware_setmode(uint32_t w, uint32_t h, uint32_t bpp) "%dx%d @ %d bpp"
 vmware_verify_rect_less_than_zero(const char *name, const char *param, int x) "%s: %s was < 0 (%d)"
 vmware_verify_rect_greater_than_bound(const char *name, const char *param, int bound, int x) "%s: %s was > %d (%d)"
 vmware_verify_rect_surface_bound_exceeded(const char *name, const char *component, int bound, const char *param1, int value1, const char *param2, int value2) "%s: %s > %d (%s: %d, %s, %d)"
+vmware_update_rect_delayed_flush(void) "display update FIFO full - forcing flush"
 
 # virtio-gpu-base.c
 virtio_gpu_features(bool virgl) "virgl %d"
diff --git a/hw/display/vmware_vga.c b/hw/display/vmware_vga.c
index 0d32a605a0..e6943005e3 100644
--- a/hw/display/vmware_vga.c
+++ b/hw/display/vmware_vga.c
@@ -80,7 +80,7 @@ struct vmsvga_state_s {
     struct vmsvga_rect_s {
         int x, y, w, h;
     } redraw_fifo[REDRAW_FIFO_LEN];
-    int redraw_fifo_first, redraw_fifo_last;
+    int redraw_fifo_last;
 };
 
 #define TYPE_VMWARE_SVGA "vmware-svga"
@@ -372,33 +372,39 @@ static inline void vmsvga_update_rect(struct vmsvga_state_s *s,
     dpy_gfx_update(s->vga.con, x, y, w, h);
 }
 
-static inline void vmsvga_update_rect_delayed(struct vmsvga_state_s *s,
-                int x, int y, int w, int h)
-{
-    struct vmsvga_rect_s *rect = &s->redraw_fifo[s->redraw_fifo_last++];
-
-    s->redraw_fifo_last &= REDRAW_FIFO_LEN - 1;
-    rect->x = x;
-    rect->y = y;
-    rect->w = w;
-    rect->h = h;
-}
-
 static inline void vmsvga_update_rect_flush(struct vmsvga_state_s *s)
 {
     struct vmsvga_rect_s *rect;
 
     if (s->invalidated) {
-        s->redraw_fifo_first = s->redraw_fifo_last;
+        s->redraw_fifo_last = 0;
         return;
     }
     /* Overlapping region updates can be optimised out here - if someone
      * knows a smart algorithm to do that, please share.  */
-    while (s->redraw_fifo_first != s->redraw_fifo_last) {
-        rect = &s->redraw_fifo[s->redraw_fifo_first++];
-        s->redraw_fifo_first &= REDRAW_FIFO_LEN - 1;
+    for (int i = 0; i < s->redraw_fifo_last; i++) {
+        rect = &s->redraw_fifo[i];
         vmsvga_update_rect(s, rect->x, rect->y, rect->w, rect->h);
     }
+
+    s->redraw_fifo_last = 0;
+}
+
+static inline void vmsvga_update_rect_delayed(struct vmsvga_state_s *s,
+                int x, int y, int w, int h)
+{
+
+    if (s->redraw_fifo_last >= REDRAW_FIFO_LEN) {
+        trace_vmware_update_rect_delayed_flush();
+        vmsvga_update_rect_flush(s);
+    }
+
+    struct vmsvga_rect_s *rect = &s->redraw_fifo[s->redraw_fifo_last++];
+
+    rect->x = x;
+    rect->y = y;
+    rect->w = w;
+    rect->h = h;
 }
 
 #ifdef HW_RECT_ACCEL
@@ -1151,7 +1157,6 @@ static void vmsvga_reset(DeviceState *dev)
     s->config = 0;
     s->svgaid = SVGA_ID;
     s->cursor.on = 0;
-    s->redraw_fifo_first = 0;
     s->redraw_fifo_last = 0;
     s->syncing = 0;
 
-- 
2.34.1