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BACKPORT: x86: add TSC_CONSTANT_RATE option

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Some boards use the local apic for udelay(), but they also provide
their own implementation of udelay() for SMM. The reason for using
the local apic for udelay() in ramstage is to not have to pay the
penalty of calibrating the TSC frequency. Therefore provide a
TSC_CONSTANT_RATE option to indicate that TSC calibration is not
needed. Instead rely on the presence of a tsc_freq_mhz() function
provided by the cpu/board.  Additionally, assume that if
TSC_CONSTANT_RATE is selected the udelay() function in SMM will
be the tsc.

BUG=None
BRANCH=None
TEST=Compiled and booted

Change-Id: Ic7096b7f5c9dec26a3f0441e6715fe02b15d44db
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/50453
Reviewed-by: Stefan Reinauer <reinauer@google.com>
This commit is contained in:
Aaron Durbin 2013-05-01 15:27:09 -05:00 • committed by ChromeBot
commit f024361729
4 changed files with 39 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

7
src/cpu/x86/Kconfig
View file

@ -25,6 +25,13 @@ config UDELAY_TSC
bool
default n
config TSC_CONSTANT_RATE
def_bool n
depends on UDELAY_TSC
help
This option asserts that the TSC ticks at a known constant rate.
Therefore, no TSC calibration is required.
config TSC_MONOTONIC_TIMER
def_bool n
depends on UDELAY_TSC

4
src/cpu/x86/tsc/Makefile.inc
View file

@ -1,2 +1,6 @@
ramstage-$(CONFIG_UDELAY_TSC) += delay_tsc.c
romstage-$(CONFIG_TSC_CONSTANT_RATE) += delay_tsc.c
ifeq ($(CONFIG_HAVE_SMI_HANDLER),y)
smm-$(CONFIG_TSC_CONSTANT_RATE) += delay_tsc.c
endif

27
src/cpu/x86/tsc/delay_tsc.c
View file

@ -5,8 +5,16 @@
#include <smp/spinlock.h>
#include <delay.h>
#if !defined(__PRE_RAM__)
static unsigned long clocks_per_usec;
#if CONFIG_TSC_CONSTANT_RATE
static unsigned long calibrate_tsc(void)
{
return tsc_freq_mhz();
}
#else /* CONFIG_TSC_CONSTANT_RATE */
#if !CONFIG_TSC_CALIBRATE_WITH_IO
#define CLOCK_TICK_RATE 1193180U /* Underlying HZ */
@ -139,6 +147,7 @@ static unsigned long long calibrate_tsc(void)
#endif /* CONFIG_TSC_CALIBRATE_WITH_IO */
#endif /* CONFIG_TSC_CONSTANT_RATE */
void init_timer(void)
{
@ -148,15 +157,27 @@ void init_timer(void)
}
}
static inline unsigned long get_clocks_per_usec(void)
{
init_timer();
return clocks_per_usec;
}
#else /* !defined(__PRE_RAM__) */
/* romstage calls into cpu/board specific function every time. */
static inline unsigned long get_clocks_per_usec(void)
{
return tsc_freq_mhz();
}
#endif /* !defined(__PRE_RAM__) */
void udelay(unsigned us)
{
unsigned long long count;
unsigned long long stop;
unsigned long long clocks;
init_timer();
clocks = us;
clocks *= clocks_per_usec;
clocks *= get_clocks_per_usec();
count = rdtscll();
stop = clocks + count;
while(stop > count) {
@ -165,7 +186,7 @@ void udelay(unsigned us)
}
}
#if CONFIG_TSC_MONOTONIC_TIMER
#if CONFIG_TSC_MONOTONIC_TIMER && !defined(__PRE_RAM__) && !defined(__SMM__)
#include <timer.h>
static struct monotonic_counter {

4
src/include/cpu/x86/tsc.h
View file

@ -40,4 +40,8 @@ static inline unsigned long long rdtscll(void)
}
#endif
#if CONFIG_TSC_CONSTANT_RATE
unsigned long tsc_freq_mhz(void);
#endif
#endif /* CPU_X86_TSC_H */