vga: Add mechanism to force the use of a shadow surface

This prevents surface sharing which will be necessary to
fix cirrus HW cursor support.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

2 files changed, 16 insertions, 2 deletions

diff --git a/hw/display/vga.c b/hw/display/vga.c
index 52eaf05659..a620c07864 100644
--- a/hw/display/vga.c
+++ b/hw/display/vga.c
@@ -1436,6 +1436,7 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
     uint8_t *d;
     uint32_t v, addr1, addr;
     vga_draw_line_func *vga_draw_line = NULL;
+    bool share_surface;
 #ifdef HOST_WORDS_BIGENDIAN
     bool byteswap = !s->big_endian_fb;
 #else
@@ -1479,21 +1480,33 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
     }
 
     depth = s->get_bpp(s);
+
+    share_surface = (!s->force_shadow) &&
+            ( depth == 32 || (depth == 16 && !byteswap) );
     if (s->line_offset != s->last_line_offset ||
         disp_width != s->last_width ||
         height != s->last_height ||
         s->last_depth != depth ||
-        s->last_byteswap != byteswap) {
-        if (depth == 32 || (depth == 16 && !byteswap)) {
+        s->last_byteswap != byteswap ||
+        share_surface != is_buffer_shared(surface)) {
+        if (share_surface) {
             pixman_format_code_t format =
                 qemu_default_pixman_format(depth, !byteswap);
             surface = qemu_create_displaysurface_from(disp_width,
                     height, format, s->line_offset,
                     s->vram_ptr + (s->start_addr * 4));
             dpy_gfx_replace_surface(s->con, surface);
+#ifdef DEBUG_VGA
+            printf("VGA: Using shared surface for depth=%d swap=%d\n",
+                   depth, byteswap);
+#endif
         } else {
             qemu_console_resize(s->con, disp_width, height);
             surface = qemu_console_surface(s->con);
+#ifdef DEBUG_VGA
+            printf("VGA: Using shadow surface for depth=%d swap=%d\n",
+                   depth, byteswap);
+#endif
         }
         s->last_scr_width = disp_width;
         s->last_scr_height = height;
diff --git a/hw/display/vga_int.h b/hw/display/vga_int.h
index ed69e064a8..72e00f2e0c 100644
--- a/hw/display/vga_int.h
+++ b/hw/display/vga_int.h
@@ -151,6 +151,7 @@ typedef struct VGACommonState {
     uint32_t last_scr_width, last_scr_height; /* in pixels */
     uint32_t last_depth; /* in bits */
     bool last_byteswap;
+    bool force_shadow;
     uint8_t cursor_start, cursor_end;
     bool cursor_visible_phase;
     int64_t cursor_blink_time;