[PATCH 1/1] hw/display: expose linear framebuffer address in Bochs VBE registers

[Liav Albani <liavalb@gmail.com>]

This is quite useful on the isa-vga device, because it lets guest drivers
to determine where is the framebuffer located in physical memory instead
of blindly hardcoding an address. It also allows future movements of the
framebuffer to other locations.

Signed-off-by: Liav Albani <liavalb@gmail.com>
---
 hw/display/bochs-display.c     | 10 +++++++++-
 hw/display/vga.c               | 13 +++++++++++--
 include/hw/display/bochs-vbe.h |  7 ++++++-
 3 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/hw/display/bochs-display.c b/hw/display/bochs-display.c
index 8ed734b195..aa3aa51e2f 100644
--- a/hw/display/bochs-display.c
+++ b/hw/display/bochs-display.c
@@ -77,9 +77,17 @@ static uint64_t bochs_display_vbe_read(void *ptr, hwaddr addr,
 
     switch (index) {
     case VBE_DISPI_INDEX_ID:
-        return VBE_DISPI_ID5;
+        return VBE_DISPI_ID6;
     case VBE_DISPI_INDEX_VIDEO_MEMORY_64K:
         return s->vgamem / (64 * KiB);
+    case VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS1:
+        return (s->vram.addr) & 0xffff;
+    case VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS2:
+        return (s->vram.addr >> 16) & 0xffff;
+    case VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS3:
+        return (s->vram.addr >> 32) & 0xffff;
+    case VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS4:
+        return (s->vram.addr >> 48) & 0xffff;
     }
 
     if (index >= ARRAY_SIZE(s->vbe_regs)) {
diff --git a/hw/display/vga.c b/hw/display/vga.c
index 50ecb1ad02..9d91946987 100644
--- a/hw/display/vga.c
+++ b/hw/display/vga.c
@@ -727,6 +727,14 @@ uint32_t vbe_ioport_read_data(void *opaque, uint32_t addr)
         }
     } else if (s->vbe_index == VBE_DISPI_INDEX_VIDEO_MEMORY_64K) {
         val = s->vbe_size / (64 * KiB);
+    } else if (s->vbe_index == VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS1) {
+        val = (s->vram.addr) & 0xffff;
+    } else if (s->vbe_index == VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS2) {
+        val = (s->vram.addr >> 16) & 0xffff;
+    } else if (s->vbe_index == VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS3) {
+        val = (s->vram.addr >> 32) & 0xffff;
+    } else if (s->vbe_index == VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS4) {
+        val = (s->vram.addr >> 48) & 0xffff;
     } else {
         val = 0;
     }
@@ -753,7 +761,8 @@ void vbe_ioport_write_data(void *opaque, uint32_t addr, uint32_t val)
                 val == VBE_DISPI_ID2 ||
                 val == VBE_DISPI_ID3 ||
                 val == VBE_DISPI_ID4 ||
-                val == VBE_DISPI_ID5) {
+                val == VBE_DISPI_ID5 ||
+                val == VBE_DISPI_ID6) {
                 s->vbe_regs[s->vbe_index] = val;
             }
             break;
@@ -1830,7 +1839,7 @@ void vga_common_reset(VGACommonState *s)
     s->bank_offset = 0;
     s->vbe_index = 0;
     memset(s->vbe_regs, '\0', sizeof(s->vbe_regs));
-    s->vbe_regs[VBE_DISPI_INDEX_ID] = VBE_DISPI_ID5;
+    s->vbe_regs[VBE_DISPI_INDEX_ID] = VBE_DISPI_ID6;
     s->vbe_start_addr = 0;
     s->vbe_line_offset = 0;
     s->vbe_bank_mask = (s->vram_size >> 16) - 1;
diff --git a/include/hw/display/bochs-vbe.h b/include/hw/display/bochs-vbe.h
index bc2f046eee..383474b9d1 100644
--- a/include/hw/display/bochs-vbe.h
+++ b/include/hw/display/bochs-vbe.h
@@ -19,8 +19,12 @@
 #define VBE_DISPI_INDEX_VIRT_HEIGHT     0x7
 #define VBE_DISPI_INDEX_X_OFFSET        0x8
 #define VBE_DISPI_INDEX_Y_OFFSET        0x9
-#define VBE_DISPI_INDEX_NB              0xa /* size of vbe_regs[] */
 #define VBE_DISPI_INDEX_VIDEO_MEMORY_64K 0xa /* read-only, not in vbe_regs */
+#define VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS1 0xb /* read-only, not in vbe_regs */
+#define VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS2 0xc /* read-only, not in vbe_regs */
+#define VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS3 0xd /* read-only, not in vbe_regs */
+#define VBE_DISPI_VIDEO_MEMORY_PHYSICAL_ADDRESS4 0xe /* read-only, not in vbe_regs */
+#define VBE_DISPI_INDEX_NB              0xe /* size of vbe_regs[] */
 
 /* VBE_DISPI_INDEX_ID */
 #define VBE_DISPI_ID0                   0xB0C0
@@ -29,6 +33,7 @@
 #define VBE_DISPI_ID3                   0xB0C3
 #define VBE_DISPI_ID4                   0xB0C4
 #define VBE_DISPI_ID5                   0xB0C5
+#define VBE_DISPI_ID6                   0xB0C6
 
 /* VBE_DISPI_INDEX_ENABLE */
 #define VBE_DISPI_DISABLED              0x00
-- 
2.37.3