vgabios: Simplify planar4 vgafb code.

Don't bother programming the vga registers to manipulate the
framebuffer when in planar4 mode.  Instead, just switch between the
four planes and do the manipulation with regular reads and writes.
This makes the code simpler to understand (the vga hardware
manipulations are arcane and complex).

Note, this could make text scrolling in planar4 mode slower and more
likely to result in tearing.  However, it's unlikely anything
important uses the vgabios in planar4 mode.

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

3 files changed, 59 insertions, 49 deletions

diff --git a/vgasrc/stdvga.c b/vgasrc/stdvga.c
index d1841bf..0fab905 100644
--- a/vgasrc/stdvga.c
+++ b/vgasrc/stdvga.c
@@ -159,6 +159,20 @@ stdvga_set_text_block_specifier(u8 spec)
     stdvga_sequ_write(0x03, spec);
 }
 
+// Enable reads and writes to the given "plane" when in planar4 mode.
+void
+stdvga_planar4_plane(int plane)
+{
+    if (plane < 0) {
+        // Return to default mode (read plane0, write all planes)
+        stdvga_sequ_write(0x02, 0x0f);
+        stdvga_grdc_write(0x04, 0);
+    } else {
+        stdvga_sequ_write(0x02, 1<<plane);
+        stdvga_grdc_write(0x04, plane);
+    }
+}
+
 
 /****************************************************************
  * Font loading
diff --git a/vgasrc/stdvga.h b/vgasrc/stdvga.h
index c19b21f..ee14358 100644
--- a/vgasrc/stdvga.h
+++ b/vgasrc/stdvga.h
@@ -124,6 +124,7 @@ void stdvga_save_dac_state(u16 seg, struct saveDACcolors *info);
 void stdvga_restore_dac_state(u16 seg, struct saveDACcolors *info);
 void stdvga_perform_gray_scale_summing(u16 start, u16 count);
 void stdvga_set_text_block_specifier(u8 spec);
+void stdvga_planar4_plane(int plane);
 void stdvga_load_font(u16 seg, void *src_far, u16 count
                       , u16 start, u8 destflags, u8 fontsize);
 u16 stdvga_get_crtc(void);
diff --git a/vgasrc/vgafb.c b/vgasrc/vgafb.c
index b6daba6..71a5719 100644
--- a/vgasrc/vgafb.c
+++ b/vgasrc/vgafb.c
@@ -8,7 +8,7 @@
 #include "biosvar.h" // GET_BDA
 #include "util.h" // memset_far
 #include "vgahw.h" // vgahw_find_mode
-#include "stdvga.h" // stdvga_grdc_write
+#include "stdvga.h" // stdvga_planar4_plane
 
 
 /****************************************************************
@@ -55,19 +55,22 @@ scroll_pl4(struct vgamode_s *vmode_g, int nblines, int attr
         src_far = dest_far - nblines * cheight * stride;
         stride = -stride;
     }
+    if (attr < 0)
+        attr = 0;
     int cols = lr.x - ul.x + 1;
     int rows = lr.y - ul.y + 1;
-    if (nblines < rows) {
-        stdvga_grdc_write(0x05, 0x01);
-        dest_far = memcpy_stride(SEG_GRAPH, dest_far, src_far, cols * cwidth
+    int i;
+    for (i=0; i<4; i++) {
+        stdvga_planar4_plane(i);
+        void *dest = dest_far;
+        if (nblines < rows)
+            dest = memcpy_stride(SEG_GRAPH, dest, src_far, cols * cwidth
                                  , stride, (rows - nblines) * cheight);
+        u8 pixels = (attr & (1<<i)) ? 0xff : 0x00;
+        memset_stride(SEG_GRAPH, dest, pixels, cols * cwidth
+                      , stride, nblines * cheight);
     }
-    if (attr < 0)
-        attr = 0;
-    stdvga_grdc_write(0x05, 0x02);
-    memset_stride(SEG_GRAPH, dest_far, attr, cols * cwidth
-                  , stride, nblines * cheight);
-    stdvga_grdc_write(0x05, 0x00);
+    stdvga_planar4_plane(-1);
 }
 
 static void
@@ -88,6 +91,8 @@ scroll_cga(struct vgamode_s *vmode_g, int nblines, int attr
         src_far = dest_far - nblines * cheight * stride;
         stride = -stride;
     }
+    if (attr < 0)
+        attr = 0;
     int cols = lr.x - ul.x + 1;
     int rows = lr.y - ul.y + 1;
     if (nblines < rows) {
@@ -96,8 +101,6 @@ scroll_cga(struct vgamode_s *vmode_g, int nblines, int attr
         dest_far = memcpy_stride(SEG_CTEXT, dest_far, src_far, cols * cwidth
                                  , stride, (rows - nblines) * cheight);
     }
-    if (attr < 0)
-        attr = 0;
     memset_stride(SEG_CTEXT, dest_far + 0x2000, attr, cols * cwidth
                   , stride, nblines * cheight);
     memset_stride(SEG_CTEXT, dest_far, attr, cols * cwidth
@@ -122,13 +125,13 @@ scroll_lin(struct vgamode_s *vmode_g, int nblines, int attr
         src_far = dest_far - nblines * cheight * stride;
         stride = -stride;
     }
+    if (attr < 0)
+        attr = 0;
     int cols = lr.x - ul.x + 1;
     int rows = lr.y - ul.y + 1;
     if (nblines < rows)
         dest_far = memcpy_stride(SEG_GRAPH, dest_far, src_far, cols * cwidth
                                  , stride, (rows - nblines) * cheight);
-    if (attr < 0)
-        attr = 0;
     memset_stride(SEG_GRAPH, dest_far, attr, cols * cwidth
                   , stride, nblines * cheight);
 }
@@ -151,15 +154,15 @@ scroll_text(struct vgamode_s *vmode_g, int nblines, int attr
         src_far = dest_far - nblines * cheight * stride;
         stride = -stride;
     }
+    if (attr < 0)
+        attr = 0x07;
+    attr = (attr << 8) | ' ';
     int cols = lr.x - ul.x + 1;
     int rows = lr.y - ul.y + 1;
     u16 seg = GET_GLOBAL(vmode_g->sstart);
     if (nblines < rows)
         dest_far = memcpy_stride(seg, dest_far, src_far, cols * cwidth
                                  , stride, (rows - nblines) * cheight);
-    if (attr < 0)
-        attr = 0x07;
-    attr = (attr << 8) | ' ';
     memset16_stride(seg, dest_far, attr, cols * cwidth
                     , stride, nblines * cheight);
 }
@@ -217,29 +220,20 @@ write_gfx_char_pl4(struct vgamode_s *vmode_g
     }
     u16 addr = cp.x + cp.y * cheight * nbcols;
     u16 src = ca.car * cheight;
-    stdvga_sequ_write(0x02, 0x0f);
-    stdvga_grdc_write(0x05, 0x02);
-    if (ca.attr & 0x80)
-        stdvga_grdc_write(0x03, 0x18);
-    else
-        stdvga_grdc_write(0x03, 0x00);
-    u8 i;
-    for (i = 0; i < cheight; i++) {
-        u8 *dest_far = (void*)(addr + i * nbcols);
-        u8 j;
-        for (j = 0; j < 8; j++) {
-            u8 mask = 0x80 >> j;
-            stdvga_grdc_write(0x08, mask);
-            GET_FARVAR(SEG_GRAPH, *(volatile u8*)dest_far);
-            if (GET_GLOBAL(fdata_g[src + i]) & mask)
-                SET_FARVAR(SEG_GRAPH, *dest_far, ca.attr & 0x0f);
-            else
-                SET_FARVAR(SEG_GRAPH, *dest_far, 0x00);
+    int i;
+    for (i=0; i<4; i++) {
+        stdvga_planar4_plane(i);
+        u8 colors = ((ca.attr & (1<<i)) ? 0xff : 0x00);
+        int j;
+        for (j = 0; j < cheight; j++) {
+            u8 *dest_far = (void*)(addr + j * nbcols);
+            u8 pixels = colors & GET_GLOBAL(fdata_g[src + j]);
+            if (ca.attr & 0x80)
+                pixels ^= GET_FARVAR(SEG_GRAPH, *dest_far);
+            SET_FARVAR(SEG_GRAPH, *dest_far, pixels);
         }
     }
-    stdvga_grdc_write(0x08, 0xff);
-    stdvga_grdc_write(0x05, 0x00);
-    stdvga_grdc_write(0x03, 0x00);
+    stdvga_planar4_plane(-1);
 }
 
 static void
@@ -407,20 +401,20 @@ vgafb_write_pixel(u8 color, u16 x, u16 y)
     if (!vmode_g)
         return;
 
-    u8 *addr_far, mask, attr, data;
+    u8 *addr_far, mask, attr, data, i;
     switch (GET_GLOBAL(vmode_g->memmodel)) {
     case MM_PLANAR:
         addr_far = (void*)(x / 8 + y * GET_BDA(video_cols));
         mask = 0x80 >> (x & 0x07);
-        stdvga_grdc_write(0x08, mask);
-        stdvga_grdc_write(0x05, 0x02);
-        GET_FARVAR(SEG_GRAPH, *(volatile u8*)addr_far);
-        if (color & 0x80)
-            stdvga_grdc_write(0x03, 0x18);
-        SET_FARVAR(SEG_GRAPH, *addr_far, color);
-        stdvga_grdc_write(0x08, 0xff);
-        stdvga_grdc_write(0x05, 0x00);
-        stdvga_grdc_write(0x03, 0x00);
+        for (i=0; i<4; i++) {
+            stdvga_planar4_plane(i);
+            u8 colors = (color & (1<<i)) ? 0xff : 0x00;
+            u8 orig = GET_FARVAR(SEG_GRAPH, *addr_far);
+            if (color & 0x80)
+                colors ^= orig;
+            SET_FARVAR(SEG_GRAPH, *addr_far, (colors & mask) | (orig & ~mask));
+        }
+        stdvga_planar4_plane(-1);
         break;
     case MM_CGA:
         if (GET_GLOBAL(vmode_g->depth) == 2)
@@ -470,11 +464,12 @@ vgafb_read_pixel(u16 x, u16 y)
         mask = 0x80 >> (x & 0x07);
         attr = 0x00;
         for (i = 0; i < 4; i++) {
-            stdvga_grdc_write(0x04, i);
+            stdvga_planar4_plane(i);
             data = GET_FARVAR(SEG_GRAPH, *addr_far) & mask;
             if (data > 0)
                 attr |= (0x01 << i);
         }
+        stdvga_planar4_plane(-1);
         break;
     case MM_CGA:
         addr_far = (void*)((x >> 2) + (y >> 1) * 80);