[PATCH 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 firstly increases the screen update FIFO size to ensure it's
large enough to accomodate all updates deferred in a given screen
refresh cycle.

When updating the screen all updates are applied to ensure the display
output is rendered correctly.

Signed-off-by: Carwyn Ellis <carwynellis@gmail.com>
---
 hw/display/vmware_vga.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/hw/display/vmware_vga.c b/hw/display/vmware_vga.c
index 8080e085d1..28556f39c6 100644
--- a/hw/display/vmware_vga.c
+++ b/hw/display/vmware_vga.c
@@ -82,7 +82,7 @@ struct vmsvga_state_s {
     uint32_t fifo_next;
     uint32_t fifo_stop;
 
-#define REDRAW_FIFO_LEN  512
+#define REDRAW_FIFO_LEN  8192
     struct vmsvga_rect_s {
         int x, y, w, h;
     } redraw_fifo[REDRAW_FIFO_LEN];
@@ -385,7 +385,14 @@ static inline void vmsvga_update_rect_delayed(struct 
vmsvga_state_s *s,
 {
     struct vmsvga_rect_s *rect = &s->redraw_fifo[s->redraw_fifo_last++];
 
-    s->redraw_fifo_last &= REDRAW_FIFO_LEN - 1;
+    if (s->redraw_fifo_last >= REDRAW_FIFO_LEN) {
+        VMWARE_VGA_DEBUG("%s: Discarding updates - FIFO length %d exceeded\n",
+            "vmsvga_update_rect_delayed",
+            REDRAW_FIFO_LEN
+        );
+        s->redraw_fifo_last = REDRAW_FIFO_LEN - 1;
+    }
+
     rect->x = x;
     rect->y = y;
     rect->w = w;
@@ -402,11 +409,13 @@ static inline void vmsvga_update_rect_flush(struct 
vmsvga_state_s *s)
     }
     /* 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_first = 0;
+    s->redraw_fifo_last = 0;
 }
 
 #ifdef HW_RECT_ACCEL
@@ -607,13 +616,14 @@ static inline uint32_t vmsvga_fifo_read(struct 
vmsvga_state_s *s)
 static void vmsvga_fifo_run(struct vmsvga_state_s *s)
 {
     uint32_t cmd, colour;
-    int args, len, maxloop = 1024;
+    int args, len = 1024;
     int x, y, dx, dy, width, height;
     struct vmsvga_cursor_definition_s cursor;
     uint32_t cmd_start;
 
     len = vmsvga_fifo_length(s);
-    while (len > 0 && --maxloop > 0) {
+
+    while (len > 0) {
         /* May need to go back to the start of the command if incomplete */
         cmd_start = s->fifo_stop;
 
-- 
2.34.1