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Garbage-collect ACPI-safe timer and friends
In 2001 when the ACPI timer was introduced, it included code to check
for a bug present in some Pentium II and Pentium III chipsets; if the
bug was found to be present, ACPI-safe (which was slower but had a
workaround for the bug) would be used rather than ACPI-fast (which
read the same timer but without the workaround).
In a8b89dff6a
(September 2021) I disabled this check by default,
with a loader tunable available to re-enable it; I announced at the
time that it would go away in FreeBSD 15 if I didn't receive any
reports of problems. I have received no such problems, so this code
is now going away.
The debug.acpi.timer_test loader variable triggered a lengthy (in fact,
infinitely long) test of the ACPI timer and appears to have been
introduced as part of the process of writing the ACPI timer (and the
associated ACPI-safe workaround) in 2001; since we are dropping support
for systems with this ACPI bug, there is no need to keep that test code
either.
This commit is contained in:
parent
3465f14dac
commit
00d061855d
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@ -74,11 +74,6 @@ static void acpi_timer_suspend_handler(struct timecounter *);
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static u_int acpi_timer_get_timecount(struct timecounter *tc);
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static u_int acpi_timer_get_timecount_safe(struct timecounter *tc);
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static int acpi_timer_sysctl_freq(SYSCTL_HANDLER_ARGS);
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static void acpi_timer_boot_test(void);
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static int acpi_timer_test(void);
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static int acpi_timer_test_enabled = 0;
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TUNABLE_INT("hw.acpi.timer_test_enabled", &acpi_timer_test_enabled);
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static device_method_t acpi_timer_methods[] = {
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DEVMETHOD(device_identify, acpi_timer_identify),
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@ -192,8 +187,6 @@ acpi_timer_probe(device_t dev)
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acpi_timer_timecounter.tc_counter_mask = 0x00ffffff;
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acpi_timer_timecounter.tc_frequency = acpi_timer_frequency;
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acpi_timer_timecounter.tc_flags = TC_FLAGS_SUSPEND_SAFE;
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if (testenv("debug.acpi.timer_test"))
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acpi_timer_boot_test();
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/*
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* If all tests of the counter succeed, use the ACPI-fast method. If
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@ -203,19 +196,11 @@ acpi_timer_probe(device_t dev)
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j = 0;
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if (bootverbose)
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printf("ACPI timer:");
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for (i = 0; i < 10; i++)
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j += acpi_timer_test();
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if (bootverbose)
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printf(" -> %d\n", j);
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if (j == 10) {
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acpi_timer_timecounter.tc_name = "ACPI-fast";
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acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount;
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acpi_timer_timecounter.tc_quality = 900;
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} else {
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acpi_timer_timecounter.tc_name = "ACPI-safe";
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acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount_safe;
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acpi_timer_timecounter.tc_quality = 850;
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}
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acpi_timer_timecounter.tc_name = "ACPI-fast";
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acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount;
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acpi_timer_timecounter.tc_quality = 900;
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tc_init(&acpi_timer_timecounter);
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device_set_descf(dev, "%d-bit timer at %u.%06uMHz",
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@ -368,108 +353,3 @@ SYSCTL_PROC(_machdep, OID_AUTO, acpi_timer_freq,
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CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 0,
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acpi_timer_sysctl_freq, "I",
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"ACPI timer frequency");
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/*
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* Some ACPI timers are known or believed to suffer from implementation
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* problems which can lead to erroneous values being read. This function
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* tests for consistent results from the timer and returns 1 if it believes
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* the timer is consistent, otherwise it returns 0.
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*
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* It appears the cause is that the counter is not latched to the PCI bus
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* clock when read:
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*
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* ] 20. ACPI Timer Errata
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* ]
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* ] Problem: The power management timer may return improper result when
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* ] read. Although the timer value settles properly after incrementing,
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* ] while incrementing there is a 3nS window every 69.8nS where the
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* ] timer value is indeterminate (a 4.2% chance that the data will be
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* ] incorrect when read). As a result, the ACPI free running count up
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* ] timer specification is violated due to erroneous reads. Implication:
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* ] System hangs due to the "inaccuracy" of the timer when used by
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* ] software for time critical events and delays.
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* ]
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* ] Workaround: Read the register twice and compare.
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* ] Status: This will not be fixed in the PIIX4 or PIIX4E, it is fixed
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* ] in the PIIX4M.
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*/
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#define N 2000
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static int
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acpi_timer_test(void)
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{
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uint32_t last, this;
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int delta, max, max2, min, n;
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register_t s;
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/* Skip the test based on the hw.acpi.timer_test_enabled tunable. */
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if (!acpi_timer_test_enabled)
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return (1);
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TSENTER();
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min = INT32_MAX;
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max = max2 = 0;
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/* Test the timer with interrupts disabled to get accurate results. */
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s = intr_disable();
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last = acpi_timer_read();
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for (n = 0; n < N; n++) {
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this = acpi_timer_read();
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delta = acpi_TimerDelta(this, last);
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if (delta > max) {
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max2 = max;
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max = delta;
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} else if (delta > max2)
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max2 = delta;
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if (delta < min)
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min = delta;
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last = this;
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}
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intr_restore(s);
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delta = max2 - min;
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if ((max - min > 8 || delta > 3) && vm_guest == VM_GUEST_NO)
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n = 0;
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else if (min < 0 || max == 0 || max2 == 0)
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n = 0;
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else
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n = 1;
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if (bootverbose)
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printf(" %d/%d", n, delta);
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TSEXIT();
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return (n);
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}
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#undef N
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/*
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* Test harness for verifying ACPI timer behaviour.
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* Boot with debug.acpi.timer_test set to invoke this.
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*/
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static void
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acpi_timer_boot_test(void)
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{
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uint32_t u1, u2, u3;
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u1 = acpi_timer_read();
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u2 = acpi_timer_read();
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u3 = acpi_timer_read();
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device_printf(acpi_timer_dev, "timer test in progress, reboot to quit.\n");
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for (;;) {
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/*
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* The failure case is where u3 > u1, but u2 does not fall between
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* the two, ie. it contains garbage.
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*/
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if (u3 > u1) {
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if (u2 < u1 || u2 > u3)
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device_printf(acpi_timer_dev,
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"timer is not monotonic: 0x%08x,0x%08x,0x%08x\n",
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u1, u2, u3);
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}
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u1 = u2;
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u2 = u3;
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u3 = acpi_timer_read();
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}
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}
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