Re: [PATCH v2 5/7] ati-vga: Disable GUI engine MMIO writes when CCE enabled

[BALATON Zoltan]

On Wed, 31 Dec 2025, Chad Jablonski wrote:

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 <c...@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 5f52739d33..29a89b3f80 100644
--- a/hw/display/ati.c
+++ b/hw/display/ati.c
@@ -1011,6 +1011,13 @@ 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) {

Small nit, I'd write this as

(s->cce.buffer_mode && addr >= 0x1400 && addr <= 0x1fff)

to make it shorter and to skip testing the addr when not needed.

Regards,
BALATON Zoltan

+        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);
}