[src/trunk]: src/sys/arch/i386/i386 disable the use of TSC on Cyrix CPUs and ...

[fair <fair%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/b63a4fb0e679
branches:  trunk
changeset: 582809:b63a4fb0e679
user:      fair <fair%NetBSD.org@localhost>
date:      Wed Jul 06 20:29:16 2005 +0000

description:
disable the use of TSC on Cyrix CPUs and document why:

When powersave mode is enabled, the TSC stops counting while the CPU is halted
in idle() waiting for an interrupt. This means we can't use the TSC for
interval time in microtime(9), and thus it is disabled here.

It still makes a perfectly good cycle counter for program profiling, so long
as you remember you're counting cycles, and not time. Further, if you don't
mind not using powersave mode, the TSC works just fine, so this should really
be optional. XXX

diffstat:

 sys/arch/i386/i386/identcpu.c |  43 +++++++++++++++++++++++++++++++++++++------
 1 files changed, 37 insertions(+), 6 deletions(-)

diffs (87 lines):

diff -r 9c5cc494dd73 -r b63a4fb0e679 sys/arch/i386/i386/identcpu.c
--- a/sys/arch/i386/i386/identcpu.c     Wed Jul 06 19:31:04 2005 +0000
+++ b/sys/arch/i386/i386/identcpu.c     Wed Jul 06 20:29:16 2005 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: identcpu.c,v 1.20 2005/07/06 18:35:39 fair Exp $       */
+/*     $NetBSD: identcpu.c,v 1.21 2005/07/06 20:29:16 fair Exp $       */
 
 /*-
  * Copyright (c) 1999, 2000, 2001 The NetBSD Foundation, Inc.
@@ -37,7 +37,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: identcpu.c,v 1.20 2005/07/06 18:35:39 fair Exp $");
+__KERNEL_RCSID(0, "$NetBSD: identcpu.c,v 1.21 2005/07/06 20:29:16 fair Exp $");
 
 #include "opt_cputype.h"
 #include "opt_enhanced_speedstep.h"
@@ -544,6 +544,19 @@
        }
 };
 
+/*
+ * disable the TSC such that we don't use the TSC in microtime(9)
+ * because some CPUs got the implementation wrong.
+ */
+static void
+disable_tsc(struct cpu_info *ci)
+{
+       if (cpu_feature & CPUID_TSC) {
+               cpu_feature &= ~CPUID_TSC;
+               printf("WARNING: broken TSC disabled\n");
+       }
+}
+
 void
 cyrix6x86_cpu_setup(ci)
        struct cpu_info *ci;
@@ -551,8 +564,13 @@
        /*
         * i8254 latch check routine:
         *     National Geode (formerly Cyrix MediaGX) has a serious bug in
-        *     its built-in i8254-compatible clock module.
+        *     its built-in i8254-compatible clock module (cs5510 cs5520).
         *     Set the variable 'clock_broken_latch' to indicate it.
+        *
+        * This bug is not present in the cs5530, and the flag
+        * is disabled again in sys/arch/i386/pci/pcib.c if this later
+        * model device is detected. Ideally, this work-around should not
+        * even be in here, it should be in there. XXX
         */
 
        extern int clock_broken_latch;
@@ -566,8 +584,22 @@
        }
 
        /* set up various cyrix registers */
-       /* Enable suspend on halt */
+       /*
+        * Enable suspend on halt (powersave mode).
+        * When powersave mode is enabled, the TSC stops counting
+        * while the CPU is halted in idle() waiting for an interrupt.
+        * This means we can't use the TSC for interval time in
+        * microtime(9), and thus it is disabled here.
+        *
+        * It still makes a perfectly good cycle counter
+        * for program profiling, so long as you remember you're
+        * counting cycles, and not time. Further, if you don't
+        * mind not using powersave mode, the TSC works just fine,
+        * so this should really be optional. XXX
+        */
        cyrix_write_reg(0xc2, cyrix_read_reg(0xc2) | 0x08);
+       disable_tsc(ci);
+
        /* enable access to ccr4/ccr5 */
        c3 = cyrix_read_reg(0xC3);
        cyrix_write_reg(0xC3, c3 | 0x10);
@@ -593,8 +625,7 @@
 #if defined(I586_CPU)
        switch (CPUID2MODEL(ci->ci_signature)) { /* model */
        case 4: /* WinChip C6 */
-               cpu_feature &= ~CPUID_TSC;
-               printf("WARNING: WinChip C6: broken TSC disabled\n");
+               disable_tsc(ci);
        }
 #endif
 }