xen/vgacon-keep.patch

Index: xen-unstable/xen/drivers/video/vga.c
===================================================================
--- xen-unstable.orig/xen/drivers/video/vga.c
+++ xen-unstable/xen/drivers/video/vga.c
@@ -556,7 +556,6 @@ static int vga_load_font(const struct fo
  */
 
 static int vgacon_enabled = 0;
-static int vgacon_keep    = 0;
 static int vgacon_lines   = 50;
 static const struct font_desc *font;
 
@@ -576,13 +575,16 @@ string_param("vga", opt_vga);
 void vga_init(void)
 {
     char *p;
+    int keep = 0;
 
     for ( p = opt_vga; p != NULL; p = strchr(p, ',') )
     {
         if ( *p == ',' )
             p++;
         if ( strncmp(p, "keep", 4) == 0 )
-            vgacon_keep = 1;
+            keep = 1;
+        else if ( strncmp(p, "yield", 5) == 0 )
+            keep = -1;
         else if ( strncmp(p, "text-80x", 8) == 0 )
             vgacon_lines = simple_strtoul(p + 8, NULL, 10);
         else if ( strncmp(p, "text", 4) == 0 && p[4] != '-' )
@@ -623,21 +625,48 @@ void vga_init(void)
     /* Disable cursor. */
     vga_wcrt(vgabase, VGA_CRTC_CURSOR_START, 0x20);
 
-    vgacon_enabled = 1;
+    vgacon_enabled = 3 + keep;
 }
 
 void vga_endboot(void)
 {
+    static const char *const str[] =
+    {
+        "relinquishing",
+        "auto-sensing",
+        "keeping"
+    };
+
     if ( !vgacon_enabled )
         return;
 
-    if ( !vgacon_keep )
-        vgacon_enabled = 0;
+    vgacon_enabled -= 2;
+    BUG_ON(vgacon_enabled < 0 || vgacon_enabled > 2);
         
-    printk("Xen is %s VGA console.\n",
-           vgacon_keep ? "keeping" : "relinquishing");
+    printk("Xen is %s VGA console.\n", str[vgacon_enabled]);
 }
 
+static int gfx_vga(void)
+{
+    unsigned char idx, data;
+
+    idx = vga_r(vgabase, VGA_GFX_I);
+    data = vga_rgfx(vgabase, VGA_GFX_MISC);
+    vga_w(vgabase, VGA_GFX_I, idx);
+
+    if ( data & 0x01 )
+        return 1;
+
+    /* Unfortunately many cards don't reflect their mode in the GDC
+     * miscellaneous register, bit 0 (and even fewer reflect it in the
+     * ATC mode control register, bit 0). Therefore we further check
+     * horizontal display width against our original setting. */
+    idx = vga_r(vgabase, VGA_CRT_IC);
+    data = vga_rcrt(vgabase, VGA_CRTC_H_DISP);
+    vga_w(vgabase, VGA_CRT_IC, idx);
+
+    return data != COLUMNS - 1;
+}
 
 static void put_newline(void)
 {
@@ -655,14 +684,25 @@ static void put_newline(void)
 
 void vga_putchar(int c)
 {
-    if ( !vgacon_enabled )
+    static int vga_in_gfx = -1;
+
+    switch ( vgacon_enabled )
+    {
+    case 0:
         return;
+    case 1:
+        if ( vga_in_gfx < 0 )
+            vga_in_gfx = gfx_vga();
+        break;
+    }
 
     if ( c == '\n' )
     {
-        put_newline();
+        if ( vga_in_gfx <= 0 )
+            put_newline();
+        vga_in_gfx = -1;
     }
-    else
+    else if ( vga_in_gfx <= 0 )
     {
         if ( xpos >= COLUMNS )
             put_newline();