[PATCH] NSC Geode Companion chip workaround

[Hiroshi MIURA <miura@da-cha.org>]

Cyrix MediaGX/GXm or NSC Geode have PIT bug not TSC bug. 
but in linux kernel, if CPU is Cyrix, then  TSC flag is disabled.
This is not correct way, I think.

A patch atached below is originally from  NetBSD kernel code.
In FreeBSD bug tracking system, this was discussed.

http://www.freebsd.org/cgi/query-pr.cgi?pr=6630

Here is NetBSD patch.
http://www.netbsd.org/cgi-bin/query-pr-single.pl?number=8654

in this patch, this code is activate only if you defines CONFIG_CS5520.
I've tryed several month with this patch, It seems good for me.
    trial machine: Casio CASSIOPEIA FIVA 101 and Fiva 103.
                   MediaGX 200MHz and NSC Geode 300MHz.



diff -ur kernel-source-2.4.7/arch/i386/kernel/setup.c linux/arch/i386/kernel/setup.c
--- kernel-source-2.4.7/arch/i386/kernel/setup.c	Thu Jul 12 01:31:44 2001
+++ linux/arch/i386/kernel/setup.c	Fri Aug 10 21:12:06 2001
@@ -1425,14 +1425,18 @@
 		/* GXm supports extended cpuid levels 'ala' AMD */
 		if (c->cpuid_level == 2) {
 			get_model_name(c);  /* get CPU marketing name */
+#ifndef CONFIG_CS5520
 			clear_bit(X86_FEATURE_TSC, c->x86_capability);
+#endif
 			return;
 		}
 		else {  /* MediaGX */
 			Cx86_cb[2] = (dir0_lsn & 1) ? '3' : '4';
 			p = Cx86_cb+2;
 			c->x86_model = (dir1 & 0x20) ? 1 : 2;
+#ifndef CONFIG_CS5520
 			clear_bit(X86_FEATURE_TSC, &c->x86_capability);
+#endif
 		}
 		break;
 
diff -ur kernel-source-2.4.7/arch/i386/kernel/time.c linux/arch/i386/kernel/time.c
--- kernel-source-2.4.7/arch/i386/kernel/time.c	Sat Dec 30 07:07:57 2000
+++ linux/arch/i386/kernel/time.c	Fri Aug 10 21:04:26 2001
@@ -28,6 +28,9 @@
  * 1998-12-24 Copyright (C) 1998  Andrea Arcangeli
  *	Fixed a xtime SMP race (we need the xtime_lock rw spinlock to
  *	serialize accesses to xtime/lost_ticks).
+ * 2001-02-20 Hiroshi Miura <miura@da-cha.org>
+ *      Work around for Cyrix/IBM/NSC MediaGX/GXm, NSC Geode southbridge 
+ *      PIT bug. (NSC Cx5510/5520)
  */
 
 #include <linux/errno.h>
@@ -459,6 +462,10 @@
 static void timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 {
 	int count;
+#ifdef CONFIG_CS5520
+	int count1, count2, count3;
+	int n1, n2, n3;
+#endif
 
 	/*
 	 * Here we are in the timer irq handler. We just have irqs locally
@@ -487,6 +494,7 @@
 
 		rdtscl(last_tsc_low);
 
+#ifndef CONFIG_CS5520
 		spin_lock(&i8253_lock);
 		outb_p(0x00, 0x43);     /* latch the count ASAP */
 
@@ -499,6 +507,59 @@
 	}
  
 	do_timer_interrupt(irq, NULL, regs);
+#else
+		spin_lock(&i8253_lock);
+		outb_p(0x00, 0x43);	/* latch the count ASAP */
+/* this codes comes from FreeBSD */
+		count1 = inb_p(0x40);
+		count1 |= inb(0x40) << 8;
+		count2 = inb_p(0x40);
+		count2 = inb(0x40) << 8;
+                count3 = inb_p(0x40);
+                count3 = inb(0x40) << 8;
+		spin_unlock(&i8253_lock);
+		
+		if (count1 >= count2 && count2 >= count3 && count1 - count2 < 0x200)
+			count = count2;
+		else {
+
+#define _swap_val(a, b) do { \
+	int c = a;\
+	a = b; \
+	b = c; \
+} while(0)
+	 	   /* sort values */
+		  if (count1 < count2)
+			_swap_val(count1, count2);
+		  if (count2 < count3)
+                        _swap_val(count2, count3);
+		  if (count1 < count2)
+			_swap_val(count1, count2);
+
+		  /* compare the middle value */
+		  if (count1 - count3 < 0x200)
+			count = count2;
+		  else 
+                       {
+			n1 = count2 - count3;
+			n2 = count3 - count1 + LATCH;
+			n3 = count1 - count2;
+			count = count3;
+			if (n1 >= n2) {
+			   if (n1 >= n3)
+				count = count1;
+			} else {
+			   if (n2 >= n3)
+				count = count2;
+			} 
+		  }
+	      	}
+                count = ((LATCH-1) - count) * TICK_SIZE;
+                delay_at_last_interrupt = (count + LATCH/2) / LATCH;
+	}
+
+      do_timer_interrupt(irq, NULL, regs);
+#endif
 
 	write_unlock(&xtime_lock);
 
@@ -659,6 +720,9 @@
  	
 	if (cpu_has_tsc) {
 		unsigned long tsc_quotient = calibrate_tsc();
+#ifdef CONFIG_CS5520
+		if (!tsc_quotient) tsc_quotient = calibrate_tsc();
+#endif
 		if (tsc_quotient) {
 			fast_gettimeoffset_quotient = tsc_quotient;
 			use_tsc = 1;


Hiroshi Miura  --- miura@da-cha.org http://www.da-cha.org/ 
CCNA, Oracle Silver Master, Network Specialist(JITEC)
My interest: http://www.cis.com.tw/Product/WS-U50R.htm