- Implement enabling write allocate on AMD K5/K6/K6-2 cpus.

  The code was originaly contributed by Kelly Yancey
  <kbyanc@freedomnet.com> in PR i386/6269 and revised by Akio Morita
  <amorita@meadow.scphys.kyoto-u.ac.jp> and me.  Test was performed by
  Akio Morita and Toshiomi Moriki <moriki@db.is.kyushu-u.ac.jp>.
- Fix stylistic bug in identcpu.c.
- Update copyright in initcpu.c
- Fix typo in LINT.

PR:		6269 and 6270

13 files changed, 331 insertions, 31 deletions

diff --git a/sys/amd64/amd64/identcpu.c b/sys/amd64/amd64/identcpu.c
index d504941..98b9edf 100644
--- a/sys/amd64/amd64/identcpu.c
+++ b/sys/amd64/amd64/identcpu.c
@@ -36,7 +36,7 @@
  * SUCH DAMAGE.
  *
  *	from: Id: machdep.c,v 1.193 1996/06/18 01:22:04 bde Exp
- *	$Id: identcpu.c,v 1.50 1998/07/11 05:59:34 bde Exp $
+ *	$Id: identcpu.c,v 1.51 1998/07/11 07:45:28 bde Exp $
  */
 
 #include "opt_cpu.h"
@@ -65,6 +65,10 @@ void	i486_bzero __P((void *buf, size_t len));
 void printcpuinfo(void);	/* XXX should be in different header file */
 void finishidentcpu(void);
 void earlysetcpuclass(void);
+#if defined(I586_CPU) && defined(CPU_WT_ALLOC)
+void	enable_K5_wt_alloc(void);
+void	enable_K6_wt_alloc(void);
+#endif
 void panicifcpuunsupported(void);
 static void identifycyrix(void);
 static void print_AMD_info(void);
@@ -273,10 +277,26 @@ printcpuinfo(void)
 		case 0x560:
 			strcat(cpu_model, "K6");
 			break;
+		case 0x570:
+			strcat(cpu_model, "K6 266 (model 1)");
+			break;
+		case 0x580:
+			strcat(cpu_model, "K6-2");
+			break;
 		default:
 			strcat(cpu_model, "Unknown");
 			break;
 		}
+#ifdef CPU_WT_ALLOC
+		if ((cpu_id & 0xf00) == 0x500) {
+			if (((cpu_id & 0x0f0) > 0)
+			    && ((cpu_id & 0x0f0) < 0x60)
+			    && ((cpu_id & 0x00f) > 3)) {
+				enable_K5_wt_alloc();
+			} else if ((cpu_id & 0x0f0) > 0x50)
+				enable_K6_wt_alloc();
+		}
+#endif
 		do_cpuid(0x80000000, regs);
 		nreg = regs[0];
 		if (nreg >= 0x80000004) {
@@ -488,7 +508,7 @@ printcpuinfo(void)
 			 * to check that all CPUs >= Pentium have a TSC and
 			 * MSRs.
 			 */
-			printf("\n  Features=0x%b", cpu_feature, 
+			printf("\n  Features=0x%b", cpu_feature,
 			"\020"
 			"\001FPU"
 			"\002VME"
@@ -636,7 +656,7 @@ identblue(void)
 
 	trap_by_rdmsr = 0;
 
-	/* 
+	/*
 	 * Cyrix 486-class CPU does not support rdmsr instruction.
 	 * The rdmsr instruction generates invalid opcode fault, and exception
 	 * will be trapped by bluetrap6() on Cyrix 486-class CPU.  The
@@ -792,7 +812,7 @@ finishidentcpu(void)
 }
 
 /*
- * This routine is called specifically to set up cpu_class before 
+ * This routine is called specifically to set up cpu_class before
  * startrtclock() uses it.  Probably this should be rearranged so that
  * startrtclock() doesn't need to run until after identifycpu() has been
  * called.  Another alternative formulation would be for this routine
@@ -816,7 +836,7 @@ print_AMD_assoc(int i)
 }
 
 static void
-print_AMD_info(void) 
+print_AMD_info(void)
 {
 	u_int regs[4];
 
diff --git a/sys/amd64/amd64/initcpu.c b/sys/amd64/amd64/initcpu.c
index 3849299..9f1f2a9 100644
--- a/sys/amd64/amd64/initcpu.c
+++ b/sys/amd64/amd64/initcpu.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) KATO Takenori, 1997.
+ * Copyright (c) KATO Takenori, 1997, 1998.
  * 
  * All rights reserved.  Unpublished rights reserved under the copyright
  * laws of Japan.
@@ -26,7 +26,7 @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- *		$Id: initcpu.c,v 1.12 1998/02/04 03:47:14 eivind Exp $
+ *		$Id: initcpu.c,v 1.13 1998/05/16 14:38:10 kato Exp $
  */
 
 #include "opt_cpu.h"
@@ -41,6 +41,11 @@
 #include <machine/specialreg.h>
 
 void initializecpu(void);
+#if defined(I586_CPU) && defined(CPU_WT_ALLOC)
+void	enable_K5_wt_alloc(void);
+void	enable_K6_wt_alloc(void);
+#endif
+
 #ifdef I486_CPU
 static void init_5x86(void);
 static void init_bluelightning(void);
@@ -439,7 +444,7 @@ static void
 init_ppro(void)
 {
 #ifndef SMP
-	quad_t	apicbase;
+	u_int64_t	apicbase;
 
 	/*
 	 * Local APIC should be diabled in UP kernel.
@@ -533,6 +538,121 @@ initializecpu(void)
 #endif /* PC98 && !UPGRADE_CPU_HW_CACHE */
 }
 
+#if defined(I586_CPU) && defined(CPU_WT_ALLOC)
+/*
+ * Enable write allocate feature of AMD processors.
+ * Following two functions require the Maxmem variable being set.
+ */
+void
+enable_K5_wt_alloc(void)
+{
+	u_int64_t	msr;
+
+	/*
+	 * Write allocate is supported only on models 1, 2, and 3, with
+	 * a stepping of 4 or greater.
+	 */
+	if (((cpu_id & 0xf0) > 0) && ((cpu_id & 0x0f) > 3)) {
+		disable_intr();
+		msr = rdmsr(0x83);		/* HWCR */
+		wrmsr(0x83, msr & !(0x10));
+
+		/*
+		 * We have to tell the chip where the top of memory is,
+		 * since video cards could have frame bufferes there,
+		 * memory-mapped I/O could be there, etc.
+		 */
+		if(Maxmem > 0)
+		  msr = Maxmem / 16;
+		else
+		  msr = 0;
+		msr |= AMD_WT_ALLOC_TME | AMD_WT_ALLOC_FRE;
+#ifdef PC98
+		if (!(inb(0x43b) & 4)) {
+			wrmsr(0x86, 0x0ff00f0);
+			msr |= AMD_WT_ALLOC_PRE;
+		}
+#else
+		/*
+		 * There is no way to know wheter 15-16M hole exists or not. 
+		 * Therefore, we disable write allocate for this range.
+		 */
+			wrmsr(0x86, 0x0ff00f0);
+			msr |= AMD_WT_ALLOC_PRE;
+#endif
+		wrmsr(0x85, msr);
+
+		msr=rdmsr(0x83);
+		wrmsr(0x83, msr|0x10); /* enable write allocate */
+
+		enable_intr();
+	}
+}
+
+void
+enable_K6_wt_alloc(void)
+{
+	quad_t	size;
+	u_int64_t	whcr;
+	u_long	eflags;
+
+	eflags = read_eflags();
+	disable_intr();
+	wbinvd();
+
+#ifdef CPU_DISABLE_CACHE
+	/*
+	 * Certain K6-2 box becomes unstable when write allocation is
+	 * enabled.
+	 */
+	/*
+	 * The AMD-K6 processer provides the 64-bit Test Register 12(TR12),
+	 * but only the Cache Inhibit(CI) (bit 3 of TR12) is suppported.
+	 * All other bits in TR12 have no effect on the processer's operation.
+	 * The I/O Trap Restart function (bit 9 of TR12) is always enabled
+	 * on the AMD-K6.
+	 */
+	wrmsr(0x0000000e, (u_int64_t)0x0008);
+#endif
+	/* Don't assume that memory size is aligned with 4M. */
+	if (Maxmem > 0)
+	  size = Maxmem / 256;
+	else
+	  size = 0;
+	size = (size + 3) / 4;
+
+	/* Limit is 508M bytes. */
+	if (size > 127)
+		size = 127;
+	whcr = rdmsr(0xc0000082);
+	whcr &= ~0x00feLL;
+	whcr |= (size << 1);
+
+#ifdef PC98
+	if (whcr & 0x00feLL) {
+		/*
+		 * If bit 2 of port 0x43b is 0, disable wrte allocate for the
+		 * 15-16M range.
+		 */
+		if (!(inb(0x43b) & 4))
+			whcr &= ~0x0001LL;
+		else
+			whcr |=  0x0001LL;
+	}
+#else
+	/*
+	 * There is no way to know wheter 15-16M hole exists or not. 
+	 * Therefore, we disable write allocate for this range.
+	 */
+	whcr &= 0x00feLL;
+#endif
+	wrmsr(0x0c0000082, whcr);
+
+	write_eflags(eflags);
+	enable_intr();
+}
+#endif /* I585_CPU && CPU_WT_ALLOC */
+
 #include "opt_ddb.h"
 #ifdef DDB
 #include <ddb/ddb.h>
diff --git a/sys/amd64/include/specialreg.h b/sys/amd64/include/specialreg.h
index c09e51a..c09c2de 100644
--- a/sys/amd64/include/specialreg.h
+++ b/sys/amd64/include/specialreg.h
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)specialreg.h	7.1 (Berkeley) 5/9/91
- *	$Id: specialreg.h,v 1.14 1997/07/21 17:53:51 fsmp Exp $
+ *	$Id: specialreg.h,v 1.15 1998/03/04 11:39:16 kato Exp $
  */
 
 #ifndef _MACHINE_SPECIALREG_H_
@@ -258,6 +258,11 @@
 #define	RCR_WT	0x10	/* Write-through. */
 #define	RCR_NLB	0x20	/* LBA# pin is not asserted. */
 
+/* AMD Write Allocate Top-Of-Memory and Control Register */
+#define	AMD_WT_ALLOC_TME	0x40000	/* top-of-memory enable */
+#define	AMD_WT_ALLOC_PRE	0x20000	/* programmable range enable */
+#define	AMD_WT_ALLOC_FRE	0x10000	/* fixed (A0000-FFFFF) range enable */
+
 
 #ifndef LOCORE
 static __inline u_char
diff --git a/sys/conf/NOTES b/sys/conf/NOTES
index dc8ccff..b74cb36 100644
--- a/sys/conf/NOTES
+++ b/sys/conf/NOTES
@@ -2,7 +2,7 @@
 # LINT -- config file for checking all the sources, tries to pull in
 #	as much of the source tree as it can.
 #
-#	$Id: LINT,v 1.481 1998/10/02 21:00:58 ken Exp $
+#	$Id: LINT,v 1.482 1998/10/05 07:45:54 obrien Exp $
 #
 # NB: You probably don't want to try running a kernel built from this
 # file.  Instead, you should start from GENERIC, and add options from
@@ -163,7 +163,8 @@ cpu		"I686_CPU"		# aka Pentium Pro(tm)
 # CPU_SUSP_HLT enables suspend on HALT.  If this option is set, CPU
 # enters suspend mode following execution of HALT instruction.
 #
-# CPU_WT_ALLOC enables write-through allocation.
+# CPU_WT_ALLOC enables write allocation on Cyrix 6x86/6x86MX and AMD
+# K5/K6/K6-2 cpus.
 #
 # CYRIX_CACHE_WORKS enables CPU cache on Cyrix 486 CPUs with cache
 # flush at hold state.
@@ -178,7 +179,7 @@ cpu		"I686_CPU"		# aka Pentium Pro(tm)
 # on a Pentium.
 #
 # NOTE 1: The options, CPU_BTB_EN, CPU_LOOP_EN, CPU_IORT,
-# CPU_LOOP_ENand CPU_RSTK_EN should no be used becasue of CPU bugs.
+# CPU_LOOP_ENand CPU_RSTK_EN should not be used becasue of CPU bugs.
 # These options may crash your system. 
 #
 # NOTE 2: If CYRIX_CACHE_REALLY_WORKS is not set, CPU cache is enabled
@@ -199,6 +200,7 @@ options		"CPU_IORT"
 options		"CPU_LOOP_EN"
 options		"CPU_RSTK_EN"
 options		"CPU_SUSP_HLT"
+options		"CPU_WT_ALLOC"
 options		"CYRIX_CACHE_WORKS"
 options		"CYRIX_CACHE_REALLY_WORKS"
 #options	"NO_F00F_HACK"
diff --git a/sys/conf/options.i386 b/sys/conf/options.i386
index d0553ee..9cb9eb8 100644
--- a/sys/conf/options.i386
+++ b/sys/conf/options.i386
@@ -1,4 +1,4 @@
-#	$Id: options.i386,v 1.88 1998/09/24 13:20:40 yokota Exp $
+#	$Id: options.i386,v 1.89 1998/09/25 17:34:48 peter Exp $
 
 DISABLE_PSE
 USER_LDT
@@ -58,6 +58,7 @@ CPU_LOOP_EN			opt_cpu.h
 CPU_RSTK_EN			opt_cpu.h
 CPU_SUSP_HLT			opt_cpu.h
 CPU_UPGRADE_HW_CACHE		opt_cpu.h
+CPU_WT_ALLOC			opt_cpu.h
 CYRIX_CACHE_WORKS		opt_cpu.h
 CYRIX_CACHE_REALLY_WORKS	opt_cpu.h
 
diff --git a/sys/conf/options.pc98 b/sys/conf/options.pc98
index da7f2f0..d18cabc 100644
--- a/sys/conf/options.pc98
+++ b/sys/conf/options.pc98
@@ -1,4 +1,4 @@
-#	$Id: options.pc98,v 1.67 1998/09/16 08:37:40 kato Exp $
+#	$Id: options.pc98,v 1.68 1998/09/28 08:23:26 kato Exp $
 DISABLE_PSE
 USER_LDT
 MATH_EMULATE		opt_math_emulate.h
@@ -57,6 +57,7 @@ CPU_LOOP_EN			opt_cpu.h
 CPU_RSTK_EN			opt_cpu.h
 CPU_SUSP_HLT			opt_cpu.h
 CPU_UPGRADE_HW_CACHE		opt_cpu.h
+CPU_WT_ALLOC			opt_cpu.h
 CYRIX_CACHE_WORKS		opt_cpu.h
 CYRIX_CACHE_REALLY_WORKS	opt_cpu.h
 
diff --git a/sys/i386/conf/LINT b/sys/i386/conf/LINT
index dc8ccff..b74cb36 100644
--- a/sys/i386/conf/LINT
+++ b/sys/i386/conf/LINT
@@ -2,7 +2,7 @@
 # LINT -- config file for checking all the sources, tries to pull in
 #	as much of the source tree as it can.
 #
-#	$Id: LINT,v 1.481 1998/10/02 21:00:58 ken Exp $
+#	$Id: LINT,v 1.482 1998/10/05 07:45:54 obrien Exp $
 #
 # NB: You probably don't want to try running a kernel built from this
 # file.  Instead, you should start from GENERIC, and add options from
@@ -163,7 +163,8 @@ cpu		"I686_CPU"		# aka Pentium Pro(tm)
 # CPU_SUSP_HLT enables suspend on HALT.  If this option is set, CPU
 # enters suspend mode following execution of HALT instruction.
 #
-# CPU_WT_ALLOC enables write-through allocation.
+# CPU_WT_ALLOC enables write allocation on Cyrix 6x86/6x86MX and AMD
+# K5/K6/K6-2 cpus.
 #
 # CYRIX_CACHE_WORKS enables CPU cache on Cyrix 486 CPUs with cache
 # flush at hold state.
@@ -178,7 +179,7 @@ cpu		"I686_CPU"		# aka Pentium Pro(tm)
 # on a Pentium.
 #
 # NOTE 1: The options, CPU_BTB_EN, CPU_LOOP_EN, CPU_IORT,
-# CPU_LOOP_ENand CPU_RSTK_EN should no be used becasue of CPU bugs.
+# CPU_LOOP_ENand CPU_RSTK_EN should not be used becasue of CPU bugs.
 # These options may crash your system. 
 #
 # NOTE 2: If CYRIX_CACHE_REALLY_WORKS is not set, CPU cache is enabled
@@ -199,6 +200,7 @@ options		"CPU_IORT"
 options		"CPU_LOOP_EN"
 options		"CPU_RSTK_EN"
 options		"CPU_SUSP_HLT"
+options		"CPU_WT_ALLOC"
 options		"CYRIX_CACHE_WORKS"
 options		"CYRIX_CACHE_REALLY_WORKS"
 #options	"NO_F00F_HACK"
diff --git a/sys/i386/conf/NOTES b/sys/i386/conf/NOTES
index dc8ccff..b74cb36 100644
--- a/sys/i386/conf/NOTES
+++ b/sys/i386/conf/NOTES
@@ -2,7 +2,7 @@
 # LINT -- config file for checking all the sources, tries to pull in
 #	as much of the source tree as it can.
 #
-#	$Id: LINT,v 1.481 1998/10/02 21:00:58 ken Exp $
+#	$Id: LINT,v 1.482 1998/10/05 07:45:54 obrien Exp $
 #
 # NB: You probably don't want to try running a kernel built from this
 # file.  Instead, you should start from GENERIC, and add options from
@@ -163,7 +163,8 @@ cpu		"I686_CPU"		# aka Pentium Pro(tm)
 # CPU_SUSP_HLT enables suspend on HALT.  If this option is set, CPU
 # enters suspend mode following execution of HALT instruction.
 #
-# CPU_WT_ALLOC enables write-through allocation.
+# CPU_WT_ALLOC enables write allocation on Cyrix 6x86/6x86MX and AMD
+# K5/K6/K6-2 cpus.
 #
 # CYRIX_CACHE_WORKS enables CPU cache on Cyrix 486 CPUs with cache
 # flush at hold state.
@@ -178,7 +179,7 @@ cpu		"I686_CPU"		# aka Pentium Pro(tm)
 # on a Pentium.
 #
 # NOTE 1: The options, CPU_BTB_EN, CPU_LOOP_EN, CPU_IORT,
-# CPU_LOOP_ENand CPU_RSTK_EN should no be used becasue of CPU bugs.
+# CPU_LOOP_ENand CPU_RSTK_EN should not be used becasue of CPU bugs.
 # These options may crash your system. 
 #
 # NOTE 2: If CYRIX_CACHE_REALLY_WORKS is not set, CPU cache is enabled
@@ -199,6 +200,7 @@ options		"CPU_IORT"
 options		"CPU_LOOP_EN"
 options		"CPU_RSTK_EN"
 options		"CPU_SUSP_HLT"
+options		"CPU_WT_ALLOC"
 options		"CYRIX_CACHE_WORKS"
 options		"CYRIX_CACHE_REALLY_WORKS"
 #options	"NO_F00F_HACK"
diff --git a/sys/i386/conf/options.i386 b/sys/i386/conf/options.i386
index d0553ee..9cb9eb8 100644
--- a/sys/i386/conf/options.i386
+++ b/sys/i386/conf/options.i386
@@ -1,4 +1,4 @@
-#	$Id: options.i386,v 1.88 1998/09/24 13:20:40 yokota Exp $
+#	$Id: options.i386,v 1.89 1998/09/25 17:34:48 peter Exp $
 
 DISABLE_PSE
 USER_LDT
@@ -58,6 +58,7 @@ CPU_LOOP_EN			opt_cpu.h
 CPU_RSTK_EN			opt_cpu.h
 CPU_SUSP_HLT			opt_cpu.h
 CPU_UPGRADE_HW_CACHE		opt_cpu.h
+CPU_WT_ALLOC			opt_cpu.h
 CYRIX_CACHE_WORKS		opt_cpu.h
 CYRIX_CACHE_REALLY_WORKS	opt_cpu.h
 
diff --git a/sys/i386/i386/identcpu.c b/sys/i386/i386/identcpu.c
index d504941..98b9edf 100644
--- a/sys/i386/i386/identcpu.c
+++ b/sys/i386/i386/identcpu.c
@@ -36,7 +36,7 @@
  * SUCH DAMAGE.
  *
  *	from: Id: machdep.c,v 1.193 1996/06/18 01:22:04 bde Exp
- *	$Id: identcpu.c,v 1.50 1998/07/11 05:59:34 bde Exp $
+ *	$Id: identcpu.c,v 1.51 1998/07/11 07:45:28 bde Exp $
  */
 
 #include "opt_cpu.h"
@@ -65,6 +65,10 @@ void	i486_bzero __P((void *buf, size_t len));
 void printcpuinfo(void);	/* XXX should be in different header file */
 void finishidentcpu(void);
 void earlysetcpuclass(void);
+#if defined(I586_CPU) && defined(CPU_WT_ALLOC)
+void	enable_K5_wt_alloc(void);
+void	enable_K6_wt_alloc(void);
+#endif
 void panicifcpuunsupported(void);
 static void identifycyrix(void);
 static void print_AMD_info(void);
@@ -273,10 +277,26 @@ printcpuinfo(void)
 		case 0x560:
 			strcat(cpu_model, "K6");
 			break;
+		case 0x570:
+			strcat(cpu_model, "K6 266 (model 1)");
+			break;
+		case 0x580:
+			strcat(cpu_model, "K6-2");
+			break;
 		default:
 			strcat(cpu_model, "Unknown");
 			break;
 		}
+#ifdef CPU_WT_ALLOC
+		if ((cpu_id & 0xf00) == 0x500) {
+			if (((cpu_id & 0x0f0) > 0)
+			    && ((cpu_id & 0x0f0) < 0x60)
+			    && ((cpu_id & 0x00f) > 3)) {
+				enable_K5_wt_alloc();
+			} else if ((cpu_id & 0x0f0) > 0x50)
+				enable_K6_wt_alloc();
+		}
+#endif
 		do_cpuid(0x80000000, regs);
 		nreg = regs[0];
 		if (nreg >= 0x80000004) {
@@ -488,7 +508,7 @@ printcpuinfo(void)
 			 * to check that all CPUs >= Pentium have a TSC and
 			 * MSRs.
 			 */
-			printf("\n  Features=0x%b", cpu_feature, 
+			printf("\n  Features=0x%b", cpu_feature,
 			"\020"
 			"\001FPU"
 			"\002VME"
@@ -636,7 +656,7 @@ identblue(void)
 
 	trap_by_rdmsr = 0;
 
-	/* 
+	/*
 	 * Cyrix 486-class CPU does not support rdmsr instruction.
 	 * The rdmsr instruction generates invalid opcode fault, and exception
 	 * will be trapped by bluetrap6() on Cyrix 486-class CPU.  The
@@ -792,7 +812,7 @@ finishidentcpu(void)
 }
 
 /*
- * This routine is called specifically to set up cpu_class before 
+ * This routine is called specifically to set up cpu_class before
  * startrtclock() uses it.  Probably this should be rearranged so that
  * startrtclock() doesn't need to run until after identifycpu() has been
  * called.  Another alternative formulation would be for this routine
@@ -816,7 +836,7 @@ print_AMD_assoc(int i)
 }
 
 static void
-print_AMD_info(void) 
+print_AMD_info(void)
 {
 	u_int regs[4];
 
diff --git a/sys/i386/i386/initcpu.c b/sys/i386/i386/initcpu.c
index 3849299..9f1f2a9 100644
--- a/sys/i386/i386/initcpu.c
+++ b/sys/i386/i386/initcpu.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) KATO Takenori, 1997.
+ * Copyright (c) KATO Takenori, 1997, 1998.
  * 
  * All rights reserved.  Unpublished rights reserved under the copyright
  * laws of Japan.
@@ -26,7 +26,7 @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- *		$Id: initcpu.c,v 1.12 1998/02/04 03:47:14 eivind Exp $
+ *		$Id: initcpu.c,v 1.13 1998/05/16 14:38:10 kato Exp $
  */
 
 #include "opt_cpu.h"
@@ -41,6 +41,11 @@
 #include <machine/specialreg.h>
 
 void initializecpu(void);
+#if defined(I586_CPU) && defined(CPU_WT_ALLOC)
+void	enable_K5_wt_alloc(void);
+void	enable_K6_wt_alloc(void);
+#endif
+
 #ifdef I486_CPU
 static void init_5x86(void);
 static void init_bluelightning(void);
@@ -439,7 +444,7 @@ static void
 init_ppro(void)
 {
 #ifndef SMP
-	quad_t	apicbase;
+	u_int64_t	apicbase;
 
 	/*
 	 * Local APIC should be diabled in UP kernel.
@@ -533,6 +538,121 @@ initializecpu(void)
 #endif /* PC98 && !UPGRADE_CPU_HW_CACHE */
 }
 
+#if defined(I586_CPU) && defined(CPU_WT_ALLOC)
+/*
+ * Enable write allocate feature of AMD processors.
+ * Following two functions require the Maxmem variable being set.
+ */
+void
+enable_K5_wt_alloc(void)
+{
+	u_int64_t	msr;
+
+	/*
+	 * Write allocate is supported only on models 1, 2, and 3, with
+	 * a stepping of 4 or greater.
+	 */
+	if (((cpu_id & 0xf0) > 0) && ((cpu_id & 0x0f) > 3)) {
+		disable_intr();
+		msr = rdmsr(0x83);		/* HWCR */
+		wrmsr(0x83, msr & !(0x10));
+
+		/*
+		 * We have to tell the chip where the top of memory is,
+		 * since video cards could have frame bufferes there,
+		 * memory-mapped I/O could be there, etc.
+		 */
+		if(Maxmem > 0)
+		  msr = Maxmem / 16;
+		else
+		  msr = 0;
+		msr |= AMD_WT_ALLOC_TME | AMD_WT_ALLOC_FRE;
+#ifdef PC98
+		if (!(inb(0x43b) & 4)) {
+			wrmsr(0x86, 0x0ff00f0);
+			msr |= AMD_WT_ALLOC_PRE;
+		}
+#else
+		/*
+		 * There is no way to know wheter 15-16M hole exists or not. 
+		 * Therefore, we disable write allocate for this range.
+		 */
+			wrmsr(0x86, 0x0ff00f0);
+			msr |= AMD_WT_ALLOC_PRE;
+#endif
+		wrmsr(0x85, msr);
+
+		msr=rdmsr(0x83);
+		wrmsr(0x83, msr|0x10); /* enable write allocate */
+
+		enable_intr();
+	}
+}
+
+void
+enable_K6_wt_alloc(void)
+{
+	quad_t	size;
+	u_int64_t	whcr;
+	u_long	eflags;
+
+	eflags = read_eflags();
+	disable_intr();
+	wbinvd();
+
+#ifdef CPU_DISABLE_CACHE
+	/*
+	 * Certain K6-2 box becomes unstable when write allocation is
+	 * enabled.
+	 */
+	/*
+	 * The AMD-K6 processer provides the 64-bit Test Register 12(TR12),
+	 * but only the Cache Inhibit(CI) (bit 3 of TR12) is suppported.
+	 * All other bits in TR12 have no effect on the processer's operation.
+	 * The I/O Trap Restart function (bit 9 of TR12) is always enabled
+	 * on the AMD-K6.
+	 */
+	wrmsr(0x0000000e, (u_int64_t)0x0008);
+#endif
+	/* Don't assume that memory size is aligned with 4M. */
+	if (Maxmem > 0)
+	  size = Maxmem / 256;
+	else
+	  size = 0;
+	size = (size + 3) / 4;
+
+	/* Limit is 508M bytes. */
+	if (size > 127)
+		size = 127;
+	whcr = rdmsr(0xc0000082);
+	whcr &= ~0x00feLL;
+	whcr |= (size << 1);
+
+#ifdef PC98
+	if (whcr & 0x00feLL) {
+		/*
+		 * If bit 2 of port 0x43b is 0, disable wrte allocate for the
+		 * 15-16M range.
+		 */
+		if (!(inb(0x43b) & 4))
+			whcr &= ~0x0001LL;
+		else
+			whcr |=  0x0001LL;
+	}
+#else
+	/*
+	 * There is no way to know wheter 15-16M hole exists or not. 
+	 * Therefore, we disable write allocate for this range.
+	 */
+	whcr &= 0x00feLL;
+#endif
+	wrmsr(0x0c0000082, whcr);
+
+	write_eflags(eflags);
+	enable_intr();
+}
+#endif /* I585_CPU && CPU_WT_ALLOC */
+
 #include "opt_ddb.h"
 #ifdef DDB
 #include <ddb/ddb.h>
diff --git a/sys/i386/include/specialreg.h b/sys/i386/include/specialreg.h
index c09e51a..c09c2de 100644
--- a/sys/i386/include/specialreg.h
+++ b/sys/i386/include/specialreg.h
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)specialreg.h	7.1 (Berkeley) 5/9/91
- *	$Id: specialreg.h,v 1.14 1997/07/21 17:53:51 fsmp Exp $
+ *	$Id: specialreg.h,v 1.15 1998/03/04 11:39:16 kato Exp $
  */
 
 #ifndef _MACHINE_SPECIALREG_H_
@@ -258,6 +258,11 @@
 #define	RCR_WT	0x10	/* Write-through. */
 #define	RCR_NLB	0x20	/* LBA# pin is not asserted. */
 
+/* AMD Write Allocate Top-Of-Memory and Control Register */
+#define	AMD_WT_ALLOC_TME	0x40000	/* top-of-memory enable */
+#define	AMD_WT_ALLOC_PRE	0x20000	/* programmable range enable */
+#define	AMD_WT_ALLOC_FRE	0x10000	/* fixed (A0000-FFFFF) range enable */
+
 
 #ifndef LOCORE
 static __inline u_char
diff --git a/sys/pc98/conf/options.pc98 b/sys/pc98/conf/options.pc98
index da7f2f0..d18cabc 100644
--- a/sys/pc98/conf/options.pc98
+++ b/sys/pc98/conf/options.pc98
@@ -1,4 +1,4 @@
-#	$Id: options.pc98,v 1.67 1998/09/16 08:37:40 kato Exp $
+#	$Id: options.pc98,v 1.68 1998/09/28 08:23:26 kato Exp $
 DISABLE_PSE
 USER_LDT
 MATH_EMULATE		opt_math_emulate.h
@@ -57,6 +57,7 @@ CPU_LOOP_EN			opt_cpu.h
 CPU_RSTK_EN			opt_cpu.h
 CPU_SUSP_HLT			opt_cpu.h
 CPU_UPGRADE_HW_CACHE		opt_cpu.h
+CPU_WT_ALLOC			opt_cpu.h
 CYRIX_CACHE_WORKS		opt_cpu.h
 CYRIX_CACHE_REALLY_WORKS	opt_cpu.h