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Garbage-collect ACPI-safe timer and friends

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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:
Colin Percival 2024-06-21 00:06:48 -07:00
parent 3465f14dac
commit 00d061855d
1 changed files with 3 additions and 123 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

126
sys/dev/acpica/acpi_timer.c
View file

@ -74,11 +74,6 @@ static void acpi_timer_suspend_handler(struct timecounter *);
static u_int acpi_timer_get_timecount(struct timecounter *tc);
static u_int acpi_timer_get_timecount_safe(struct timecounter *tc);
static int acpi_timer_sysctl_freq(SYSCTL_HANDLER_ARGS);
static void acpi_timer_boot_test(void);
static int acpi_timer_test(void);
static int acpi_timer_test_enabled = 0;
TUNABLE_INT("hw.acpi.timer_test_enabled", &acpi_timer_test_enabled);
static device_method_t acpi_timer_methods[] = {
DEVMETHOD(device_identify, acpi_timer_identify),
@ -192,8 +187,6 @@ acpi_timer_probe(device_t dev)
acpi_timer_timecounter.tc_counter_mask = 0x00ffffff;
acpi_timer_timecounter.tc_frequency = acpi_timer_frequency;
acpi_timer_timecounter.tc_flags = TC_FLAGS_SUSPEND_SAFE;
if (testenv("debug.acpi.timer_test"))
acpi_timer_boot_test();
/*
* If all tests of the counter succeed, use the ACPI-fast method. If
@ -203,19 +196,11 @@ acpi_timer_probe(device_t dev)
j = 0;
if (bootverbose)
printf("ACPI timer:");
for (i = 0; i < 10; i++)
j += acpi_timer_test();
if (bootverbose)
printf(" -> %d\n", j);
if (j == 10) {
acpi_timer_timecounter.tc_name = "ACPI-fast";
acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount;
acpi_timer_timecounter.tc_quality = 900;
} else {
acpi_timer_timecounter.tc_name = "ACPI-safe";
acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount_safe;
acpi_timer_timecounter.tc_quality = 850;
}
acpi_timer_timecounter.tc_name = "ACPI-fast";
acpi_timer_timecounter.tc_get_timecount = acpi_timer_get_timecount;
acpi_timer_timecounter.tc_quality = 900;
tc_init(&acpi_timer_timecounter);
device_set_descf(dev, "%d-bit timer at %u.%06uMHz",
@ -368,108 +353,3 @@ SYSCTL_PROC(_machdep, OID_AUTO, acpi_timer_freq,
CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 0,
acpi_timer_sysctl_freq, "I",
"ACPI timer frequency");
/*
* Some ACPI timers are known or believed to suffer from implementation
* problems which can lead to erroneous values being read. This function
* tests for consistent results from the timer and returns 1 if it believes
* the timer is consistent, otherwise it returns 0.
*
* It appears the cause is that the counter is not latched to the PCI bus
* clock when read:
*
* ] 20. ACPI Timer Errata
* ]
* ] Problem: The power management timer may return improper result when
* ] read. Although the timer value settles properly after incrementing,
* ] while incrementing there is a 3nS window every 69.8nS where the
* ] timer value is indeterminate (a 4.2% chance that the data will be
* ] incorrect when read). As a result, the ACPI free running count up
* ] timer specification is violated due to erroneous reads. Implication:
* ] System hangs due to the "inaccuracy" of the timer when used by
* ] software for time critical events and delays.
* ]
* ] Workaround: Read the register twice and compare.
* ] Status: This will not be fixed in the PIIX4 or PIIX4E, it is fixed
* ] in the PIIX4M.
*/
#define N 2000
static int
acpi_timer_test(void)
{
uint32_t last, this;
int delta, max, max2, min, n;
register_t s;
/* Skip the test based on the hw.acpi.timer_test_enabled tunable. */
if (!acpi_timer_test_enabled)
return (1);
TSENTER();
min = INT32_MAX;
max = max2 = 0;
/* Test the timer with interrupts disabled to get accurate results. */
s = intr_disable();
last = acpi_timer_read();
for (n = 0; n < N; n++) {
this = acpi_timer_read();
delta = acpi_TimerDelta(this, last);
if (delta > max) {
max2 = max;
max = delta;
} else if (delta > max2)
max2 = delta;
if (delta < min)
min = delta;
last = this;
}
intr_restore(s);
delta = max2 - min;
if ((max - min > 8 || delta > 3) && vm_guest == VM_GUEST_NO)
n = 0;
else if (min < 0 || max == 0 || max2 == 0)
n = 0;
else
n = 1;
if (bootverbose)
printf(" %d/%d", n, delta);
TSEXIT();
return (n);
}
#undef N
/*
* Test harness for verifying ACPI timer behaviour.
* Boot with debug.acpi.timer_test set to invoke this.
*/
static void
acpi_timer_boot_test(void)
{
uint32_t u1, u2, u3;
u1 = acpi_timer_read();
u2 = acpi_timer_read();
u3 = acpi_timer_read();
device_printf(acpi_timer_dev, "timer test in progress, reboot to quit.\n");
for (;;) {
/*
* The failure case is where u3 > u1, but u2 does not fall between
* the two, ie. it contains garbage.
*/
if (u3 > u1) {
if (u2 < u1 || u2 > u3)
device_printf(acpi_timer_dev,
"timer is not monotonic: 0x%08x,0x%08x,0x%08x\n",
u1, u2, u3);
}
u1 = u2;
u2 = u3;
u3 = acpi_timer_read();
}
}