vgabios: Unify page size calculations; remove page size from vgamode_s.

The previous code could obtain the page size in different ways - from
vmode_g->sslength, from SCREEN_MEM_START, or by manually multiplying
cols and rows.  Add a new func (calc_page_size) and use that in areas
that need to calculate the page size.

Convert readers of the page size to read it from the "video_pagesize"
entry in the BDA instead of recalculating it.

Remove the page size from struct vgamode_s (slength) as it is now
calculated dynamically.  The new calculated versions are different
from the existing values exported in video_param_table.  However, the
existing values (for CGA) did not look correct - I compared the values
to those exported by two other VGA BIOS manufacturers and used the
values that look more standard.

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

1 files changed, 6 insertions, 14 deletions

diff --git a/vgasrc/vgafb.c b/vgasrc/vgafb.c
index eb4ced8..b933738 100644
--- a/vgasrc/vgafb.c
+++ b/vgasrc/vgafb.c
@@ -139,10 +139,8 @@ scroll_text(struct vgamode_s *vmode_g, int nblines, int attr
 {
     int cheight = 1;
     int cwidth = 2;
-    u16 nbrows = GET_BDA(video_rows) + 1;
-    u16 nbcols = GET_BDA(video_cols);
-    int stride = nbcols * cwidth;
-    void *src_far, *dest_far = (void*)SCREEN_MEM_START(nbcols, nbrows, ul.page);
+    int stride = GET_BDA(video_cols) * cwidth;
+    void *src_far, *dest_far = (void*)(GET_BDA(video_pagesize) * ul.page);
     if (nblines >= 0) {
         dest_far += ul.y * cheight * stride + ul.x * cwidth;
         src_far = dest_far + nblines * cheight * stride;
@@ -330,12 +328,9 @@ static void
 write_text_char(struct vgamode_s *vmode_g
                 , struct cursorpos cp, struct carattr ca)
 {
-    // Get the dimensions
-    u16 nbrows = GET_BDA(video_rows) + 1;
-    u16 nbcols = GET_BDA(video_cols);
-
     // Compute the address
-    void *address_far = (void*)(SCREEN_MEM_START(nbcols, nbrows, cp.page)
+    u16 nbcols = GET_BDA(video_cols);
+    void *address_far = (void*)(GET_BDA(video_pagesize) * cp.page
                                 + (cp.x + cp.y * nbcols) * 2);
 
     if (ca.use_attr) {
@@ -386,12 +381,9 @@ vgafb_read_char(struct cursorpos cp)
         goto fail;
     }
 
-    // Get the dimensions
-    u16 nbrows = GET_BDA(video_rows) + 1;
-    u16 nbcols = GET_BDA(video_cols);
-
     // Compute the address
-    u16 *address_far = (void*)(SCREEN_MEM_START(nbcols, nbrows, cp.page)
+    u16 nbcols = GET_BDA(video_cols);
+    u16 *address_far = (void*)(GET_BDA(video_pagesize) * cp.page
                                + (cp.x + cp.y * nbcols) * 2);
     u16 v = GET_FARVAR(GET_GLOBAL(vmode_g->sstart), *address_far);
     struct carattr ca = {v, v>>8, 0};