Re: [PATCH v10 16/17] ati-vga: Implement HOST_DATA register writes

[BALATON Zoltan]

On Mon, 2 Mar 2026, Chad Jablonski wrote:

Writing to any of the HOST_DATA0-7 registers pushes the written data
into a 128-bit accumulator. When the accumulator is full a flush is
triggered to copy it to the framebuffer. A final write to HOST_DATA_LAST
will also initiate a flush. The flush itself is left for the next patch.

Unaligned HOST_DATA* writes result in, from what I can tell, undefined
behavior on real hardware. A well-behaved driver shouldn't be doing this
anyway. For that reason they are not handled here at all.

Signed-off-by: Chad Jablonski <c...@jablonski.xyz>
---
hw/display/ati.c      | 30 ++++++++++++++++++++++++++++++
hw/display/ati_dbg.c  |  9 +++++++++
hw/display/ati_int.h  |  9 +++++++++
hw/display/ati_regs.h |  9 +++++++++
4 files changed, 57 insertions(+)

diff --git a/hw/display/ati.c b/hw/display/ati.c
index 6cf243bcf9..965110c13a 100644
--- a/hw/display/ati.c
+++ b/hw/display/ati.c
@@ -1024,6 +1024,31 @@ static void ati_mm_write(void *opaque, hwaddr addr,
    case SRC_SC_BOTTOM:
        s->regs.src_sc_bottom = data & 0x3fff;
        break;
+    case HOST_DATA0:
+    case HOST_DATA1:
+    case HOST_DATA2:
+    case HOST_DATA3:
+    case HOST_DATA4:
+    case HOST_DATA5:
+    case HOST_DATA6:
+    case HOST_DATA7:
+        if (!s->host_data.active) {
+            break;
+        }
+        s->host_data.acc[s->host_data.next++] = data;
+        if (s->host_data.next >= 4) {
+            qemu_log_mask(LOG_UNIMP, "HOST_DATA flush not yet implemented\n");
+            s->host_data.next = 0;
+        }
+        break;
+    case HOST_DATA_LAST:
+        if (!s->host_data.active) {
+            break;
+        }
+        s->host_data.acc[s->host_data.next] = data;
+        qemu_log_mask(LOG_UNIMP,
+                      "HOST_DATA finish flush not yet implemented\n");
+        break;

These look quite similar so maybe it could be simpler as
case HOST_DATA7:
case HOST_DATA_LAST:
    if (!s->host_data.active) {
        break;
    }
    s->host_data.acc[s->host_data.next++] = data;
    if (s->host_data.next >= 4 || addr == HOST_DATA_LAST) {
        flush;
        s->host_data.next = 0; // is this needed? flush might reset it
    }

Regards,
BALATON Zoltan