Initial. Don't... just don't ask.

utils/setmclk.c

@@ -0,0 +1,89 @@
+/*
+   Note: Previously this program did not unlock the extended registers,
+   so it only worked if the registers happened to be unlocked.
+
+   This program sets the 'memory clock' of Cirrus 5424/26/28 cards.
+   The first three values could be set by utility programs that
+   came with my card (AVGA3), but somewhat higher values seem to work (on my
+   card at least). It may be that better and more recent Cirrus cards use a
+   higher value as boot-up default. It should depend on DRAM speed, but it
+   seems to be more dependant on the card logic.
+
+   I have the impression that many Cirrus 542x cards suffer from horrible
+   BIOS version/DRAM timing misconfigurations. Perhaps even some versions of
+   MS-Windows drivers change the MCLK register. In any case, the boot-up BIOS
+   default (0x1c) may be inappropriately low for the type of DRAM timing most
+   cards use.
+
+   Using a higher memory clock gives a very significant performance improvement;
+   with high dot clock modes (like 640x480x16M or 1150x900x256) performance can
+   be more than twice that of the standard 50 MHz clock. This goes for both
+   (VLB) framebuffer access and accelerated features (bitblt). This also helps
+   XFree86 server performance, but only if the XFree86 Cirrus driver doesn't
+   set the memory clock register (it should work for XFree86 1.3 and 2.0).
+   Use at your own risk!
+
+   Note that the 'dot clock' is something entirely different. There does not
+   seem to be much correlation between the two (i.e. if a high dot clock gives
+   screen problems, using a high memory clock is not likely to fix it, other
+   than improving speed).
+
+ */
+
+
+#define NEW_MCLK 0x1C		/* Default value */
+														 /* #define NEW_MCLK 0x26 *//* High value to test XFree86 */
+
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <vga.h>
+#include <sys/io.h>	/* For port I/O macros. */
+#define OUTB(a,d) outb(d,a)
+
+int
+main (void)
+{
+  vga_init ();
+  if (vga_getcurrentchipset () != CIRRUS)
+    {
+      printf ("Not a Cirrus.\n");
+      printf ("Continue anyway (y/n)?\n");
+      if (getchar () != 'y')
+	return -1;
+    }
+
+  /* Unlock extended registers. */
+  OUTB (0x3c4, 0x06);
+  OUTB (0x3c5, 0x12);
+
+
+  /*
+     Tested on VLB AVGA3 CL-GD5426 on 40MHz VLB
+     0x1c         50 MHz (boot-up default)
+     0x21         59
+     0x22         62
+     0x23 OK
+     0x24 OK
+     0x25 OK
+     0x26 OK              [This corresponds to the highest value
+     mentioned in the databook (which does
+     not mean that it is supposed to work
+     on all cards); the book also says the
+     parts are not specified for more than
+     50 MHz].
+     0x27 occasional loose pixels
+     0x28 occasional problems
+     0x29 some problems
+     0x2A 16M/textmode problems
+     0x2c 256/32k color problems
+   */
+  OUTB (0x3c4, 0x1f);
+  printf ("Old MCLK value: %02x\n", inb (0x3c5));
+  OUTB (0x3c4, 0x1f);
+  OUTB (0x3c5, NEW_MCLK);
+  printf ("New MCLK value: %02x\n", NEW_MCLK);
+
+  return 0;
+}