Re: [PATCH v4 1/1] ati-vga: Fix framebuffer mapping by using hardware-correct aperture sizes

[BALATON Zoltan]

On Thu, 23 Oct 2025, BALATON Zoltan wrote:

On Fri, 17 Oct 2025, Chad Jablonski wrote:

Rage 128 cards always request 64MB for their linear (framebuffer)
aperture and R100 cards always request 128MB. This is regardless
of the amount of physical VRAM on the board. The following are results
from real hardware tests:

Card VRAM PCI BAR0 CONFIG_MEMSIZE CONFIG_APER_SIZE AGP_APER_OFFSET ----------------------- ---- -------- -------------- ---------------- --------------- Rage 128 Pro Ultra TF 32MB 64MB 0x02000000 0x02000000 0x02000000 Rage 128 RF/SG AGP 16MB 64MB 0x01000000 0x02000000 0x02000000 Radeon R100 QD [Radeon 7200] 64MB 128MB 0x04000000 0x04000000 N/A Radeon RV100 QY [Radeon 7000/VE] 32MB 128MB 0x02000000 0x04000000 N/A

Previously the linear aperture (BAR0) would match the VRAM size.
This discrepancy caused issues with the X.org and XFree86 r128 drivers.
These drivers apply a mask of 0xfc000000 (2^26 = 64MB) to the linear
aperture address. If that address is not on a 64MB boundary the
framebuffer points to an incorrect memory location.

Testing shows that the Radeon R100 also has a BAR0 larger than VRAM
(128MB in this case) and the X.org radeon driver also masks to 64MB.

For Rage 128, CONFIG_APER_SIZE also differs from the previous value and
the behavior stated in the documentation. The Rage 128 register guide
states that it should contain the size of the VRAM + AGP memory. The cards
tested above show that this isn't the case. These tests also included
enabling/disabling AGP with 8MB of memory. It didn't change the
contents of CONFIG_APER_SIZE.

For both Rage 128 and R100 the CONFIG_APER_SIZE is half of the PCI BAR0 size.

Ping?

Ping^2

Signed-off-by: Chad Jablonski <c...@jablonski.xyz>
Reviewed-by: BALATON Zoltan <bala...@eik.bme.hu>
---
hw/display/ati.c     | 16 ++++++++++++++--
hw/display/ati_int.h |  5 +++++
2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/hw/display/ati.c b/hw/display/ati.c
index f7c0006a87..0b4298d078 100644
--- a/hw/display/ati.c
+++ b/hw/display/ati.c

@@ -361,7 +361,7 @@ static uint64_t ati_mm_read(void *opaque, hwaddr addr, unsigned int size) PCI_BASE_ADDRESS_0, size) & 0xfffffff0;

        break;
    case CONFIG_APER_SIZE:
-        val = s->vga.vram_size / 2;
+        val = memory_region_size(&s->linear_aper) / 2;
        break;
    case CONFIG_REG_1_BASE:
        val = pci_default_read_config(&s->dev,

@@ -952,6 +952,7 @@ static void ati_vga_realize(PCIDevice *dev, Error **errp)

{
    ATIVGAState *s = ATI_VGA(dev);
    VGACommonState *vga = &s->vga;
+    uint64_t aper_size;

#ifndef CONFIG_PIXMAN
    if (s->use_pixman != 0) {

@@ -1011,7 +1012,18 @@ static void ati_vga_realize(PCIDevice *dev, Error **errp)

    /* io space is alias to beginning of mmregs */

memory_region_init_alias(&s->io, OBJECT(s), "ati.io", &s->mm, 0, 0x100);

-    pci_register_bar(dev, 0, PCI_BASE_ADDRESS_MEM_PREFETCH, &vga->vram);
+    /*
+     * The framebuffer is at the beginning of the linear aperture. For
+     * Rage128 the upper half of the aperture is reserved for an AGP
+     * window (which we do not emulate.)
+     */
+    aper_size = s->dev_id == PCI_DEVICE_ID_ATI_RAGE128_PF ?
+                ATI_RAGE128_LINEAR_APER_SIZE : ATI_R100_LINEAR_APER_SIZE;

+ memory_region_init(&s->linear_aper, OBJECT(dev), "ati-linear-aperture0",

+                       aper_size);
+    memory_region_add_subregion(&s->linear_aper, 0, &vga->vram);
+

+ pci_register_bar(dev, 0, PCI_BASE_ADDRESS_MEM_PREFETCH, &s->linear_aper);

    pci_register_bar(dev, 1, PCI_BASE_ADDRESS_SPACE_IO, &s->io);
    pci_register_bar(dev, 2, PCI_BASE_ADDRESS_SPACE_MEMORY, &s->mm);

diff --git a/hw/display/ati_int.h b/hw/display/ati_int.h
index f5a47b82b0..708cc1dd3a 100644
--- a/hw/display/ati_int.h
+++ b/hw/display/ati_int.h
@@ -10,6 +10,7 @@
#define ATI_INT_H

#include "qemu/timer.h"
+#include "qemu/units.h"
#include "hw/pci/pci_device.h"
#include "hw/i2c/bitbang_i2c.h"
#include "vga_int.h"
@@ -29,6 +30,9 @@
/* Radeon RV100 (VE) */
#define PCI_DEVICE_ID_ATI_RADEON_QY 0x5159

+#define ATI_RAGE128_LINEAR_APER_SIZE (64 * MiB)
+#define ATI_R100_LINEAR_APER_SIZE (128 * MiB)
+
#define TYPE_ATI_VGA "ati-vga"
OBJECT_DECLARE_SIMPLE_TYPE(ATIVGAState, ATI_VGA)

@@ -97,6 +101,7 @@ struct ATIVGAState {
    QEMUCursor *cursor;
    QEMUTimer vblank_timer;
    bitbang_i2c_interface bbi2c;
+    MemoryRegion linear_aper;
    MemoryRegion io;
    MemoryRegion mm;
    ATIVGARegs regs;