commit f7f22630fdf50f6da973d9df210b7c8e32849975
author Kevin O'Connor <kevin@koconnor.net> Fri Oct 17 21:37:23 2014 -0400
committer Kevin O'Connor <kevin@koconnor.net> Mon Oct 27 11:00:32 2014 -0400
tree 16511aee5e7dc236a51210ddb00469b708bc98d8
parent 9978d49d1c858087de518a1d7391ba88aa0f5109

vgabios: Cache a pointer to the current mode struct in the BDA

Cache a pointer to the current mode 'vgamode_s' struct in the BDA to
avoid doing a linear scan of all available vga modes when the struct
is needed.

This uses an additional two bytes in the BDA (at offset 0xbc).  It's
possible this could conflict with some other software, but that seams
unlikely because that part of the BDA seems reserved for BIOS and
VGABIOS uses.  (And neither SeaBIOS nor Bochs BIOS currently make use
of that area.)

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

vgasrc/vgabios.c

diff --git a/vgasrc/vgabios.c b/vgasrc/vgabios.c
index d36b62a..fcc5b34 100644
--- a/vgasrc/vgabios.c
+++ b/vgasrc/vgabios.c
@@ -261,7 +261,10 @@
                    , sizeof(info->bda_0x49));
         memcpy_far(SEG_BDA, (void*)0x84, seg, info->bda_0x84
                    , sizeof(info->bda_0x84));
-        SET_BDA_EXT(vbe_mode, GET_FARVAR(seg, info->vbe_mode));
+        u16 vbe_mode = GET_FARVAR(seg, info->vbe_mode);
+        SET_BDA_EXT(vbe_mode, vbe_mode);
+        struct vgamode_s *vmode_g = vgahw_find_mode(vbe_mode);
+        SET_BDA_EXT(vgamode_offset, (u32)vmode_g);
         SET_IVT(0x1f, GET_FARVAR(seg, info->font0));
         SET_IVT(0x43, GET_FARVAR(seg, info->font1));
     }
@@ -276,7 +279,7 @@
 struct vgamode_s *
 get_current_mode(void)
 {
-    return vgahw_find_mode(GET_BDA_EXT(vbe_mode) & ~MF_VBEFLAGS);
+    return (void*)(GET_BDA_EXT(vgamode_offset)+0);
 }
 
 // Setup BDA after a mode switch.
@@ -302,6 +305,7 @@
     else
         SET_BDA(video_mode, 0xff);
     SET_BDA_EXT(vbe_mode, mode | (flags & MF_VBEFLAGS));
+    SET_BDA_EXT(vgamode_offset, (u32)vmode_g);
     if (memmodel == MM_TEXT) {
         SET_BDA(video_cols, width);
         SET_BDA(video_rows, height-1);

vgasrc/vgabios.h

diff --git a/vgasrc/vgabios.h b/vgasrc/vgabios.h
index 70682c9..d17b48f 100644
--- a/vgasrc/vgabios.h
+++ b/vgasrc/vgabios.h
@@ -81,6 +81,7 @@
 struct vga_bda_s {
     u8 vbe_flag;
     u16 vbe_mode;
+    u16 vgamode_offset;
 } PACKED;
 
 #define GET_BDA_EXT(var) \