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cpu/x86/tsc: Flip and rename TSC_CONSTANT_RATE to UNKNOWN_TSC_RATE

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The x86 timers are a bit of a mess. Cases where different stages use
different counters and timestamps use different counters from udelays.

The original intention was to only flip TSC_CONSTANT_RATE Kconfig
to NOT_CONSTANT_TSC_RATE. The name would be incorrect though, those
counters do run with a constant rate but we just lack tsc_freq_mhz()
implementation for three platforms.

Note that for boards with UNKNOWN_TSC_RATE=y, each stage will have a
slow run of calibrate_tsc_with_pit(). This is easy enough to fix with
followup implementation of tsc_freq_mhz() for the platforms.

Implementations with LAPIC_MONOTONIC_TIMER typically will not have
tsc_freq_mhz() implemented and default to UNKNOWN_TSC_RATE. However,
as they don't use TSC for udelay() the slow calibrate_tsc_with_pit()
is avoided.

Because x86/tsc_delay.tsc was using two different guards and nb/via/vx900
claimed UDELAY_TSC, but pulled UDELAY_IO implementation, we also switch
that romstage to use UDELAY_TSC.

Change-Id: I1690cb80295d6b006b75ed69edea28899b674b68
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33928
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
This commit is contained in:
Kyösti Mälkki
2019-10-31 14:52:20 +02:00
parent ea2bec2c4b
commit 0d6ddf8da7
32 changed files with 43 additions and 54 deletions
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23
src/cpu/x86/tsc/delay_tsc.c
View File

@ -18,26 +18,9 @@
#include <delay.h>
#include <thread.h>
static unsigned long clocks_per_usec CAR_GLOBAL;
static unsigned long calibrate_tsc(void)
{
if (CONFIG(TSC_CONSTANT_RATE))
return tsc_freq_mhz();
else
return calibrate_tsc_with_pit();
}
void init_timer(void)
{
if (!car_get_var(clocks_per_usec))
car_set_var(clocks_per_usec, calibrate_tsc());
}
static inline unsigned long get_clocks_per_usec(void)
{
init_timer();
return car_get_var(clocks_per_usec);
(void)tsc_freq_mhz();
}
void udelay(unsigned int us)
@ -51,7 +34,7 @@ void udelay(unsigned int us)
start = rdtscll();
clocks = us;
clocks *= get_clocks_per_usec();
clocks *= tsc_freq_mhz();
current = rdtscll();
while ((current - start) < clocks) {
cpu_relax();
@ -89,7 +72,7 @@ void timer_monotonic_get(struct mono_time *mt)
current_tick = rdtscll();
ticks_elapsed = current_tick - mono_counter->last_value;
ticks_per_usec = get_clocks_per_usec();
ticks_per_usec = tsc_freq_mhz();
/* Update current time and tick values only if a full tick occurred. */
if (ticks_elapsed >= ticks_per_usec) {