When the CCE engine is enabled, real hardware ignores any MMIO writes to
GUI registers (0x1400-0x1fff range). Writes made by the CCE engine are
not affected by this.

Signed-off-by: Chad Jablonski <chad@jablonski.xyz>
---
 hw/display/ati.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hw/display/ati.c b/hw/display/ati.c
index a9fe0cd0d2..82450c0331 100644
--- a/hw/display/ati.c
+++ b/hw/display/ati.c
@@ -1131,6 +1131,13 @@ static void ati_mm_write(void *opaque, hwaddr addr,
     if (addr < CUR_OFFSET || addr > CUR_CLR1 || ATI_DEBUG_HW_CURSOR) {
         trace_ati_mm_write(size, addr, ati_reg_name(addr & ~3ULL), data);
     }
+    if (addr >= 0x1400 && addr <= 0x1fff && s->cce.buffer_mode != 0) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+            "ati_mm_write: wrote 0x%lx to gui register 0x%lx while cce engine enabled, ignored.\n",
+            data, addr);
+        return;
+    }
+
     ati_reg_write(s, addr, data, size);
 }
 
-- 
2.51.2