[PATCH v3 2/2] hw/display/vmware_vga: do not discard screen updates

[Carwyn Ellis]

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.

Additionally 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 91efc88f04..0c0ffcbe42 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 0cc43a1f15..8a3c3cb8f0 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"
@@ -380,33 +380,39 @@ 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
@@ -1159,7 +1165,6 @@ 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;
 
-- 
2.35.1