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udelay: Use clock_gettime() if available and precise

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Instead of calibrating our busy loop against a coarse clock, check if
a precise clock is available and loop against that. The former is unre-
liable by definition on any modern system that may dynamically reclock
the processor.

v2: Apparently _POSIX_MONOTONIC_CLOCK being defined only means that
    the library knows about CLOCK_MONOTONIC. So check for its support
    at runtime and fall back to CLOCK_REALTIME if it's missing.

TEST=Manually added a 10s loop and compared to real time. Run
     on Linux RPi3, Linux x86 and my original use case Linux in
     VirtualBox (Linux host).

Change-Id: I85ad359823875237ada9cd027af3017d62e9a235
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/19391
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
This commit is contained in:
Nico Huber
2012-11-05 21:46:33 +01:00
parent 2d62572d1d
commit 8624e8cfa8
2 changed files with 78 additions and 0 deletions
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22
Makefile
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@ -1003,6 +1003,9 @@ FEATURE_CFLAGS += $(call debug_shell,grep -q "UTSNAME := yes" .features && print
# We could use PULLED_IN_LIBS, but that would be ugly.
FEATURE_LIBS += $(call debug_shell,grep -q "NEEDLIBZ := yes" .libdeps && printf "%s" "-lz")
FEATURE_CFLAGS += $(call debug_shell,grep -q "CLOCK_GETTIME := yes" .features && printf "%s" "-D'HAVE_CLOCK_GETTIME=1'")
FEATURE_LIBS += $(call debug_shell,grep -q "CLOCK_GETTIME := yes" .features && printf "%s" "-lrt")
LIBFLASHROM_OBJS = $(CHIP_OBJS) $(PROGRAMMER_OBJS) $(LIB_OBJS)
OBJS = $(CLI_OBJS) $(LIBFLASHROM_OBJS)
@ -1299,6 +1302,18 @@ int main(int argc, char **argv)
endef
export LINUX_I2C_TEST
define CLOCK_GETTIME_TEST
#include <time.h>
int main(int argc, char **argv)
{
struct timespec res;
clock_gettime(CLOCK_REALTIME, &res);
return 0;
}
endef
export CLOCK_GETTIME_TEST
features: compiler
@echo "FEATURES := yes" > .features.tmp
ifneq ($(NEED_LIBFTDI), )
@ -1341,6 +1356,13 @@ endif
@ { $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) .featuretest.c -o .featuretest$(EXEC_SUFFIX) >&2 && \
( echo "found."; echo "UTSNAME := yes" >> .features.tmp ) || \
( echo "not found."; echo "UTSNAME := no" >> .features.tmp ) } 2>>$(BUILD_DETAILS_FILE) | tee -a $(BUILD_DETAILS_FILE)
@printf "Checking for clock_gettime support... " | tee -a $(BUILD_DETAILS_FILE)
@echo "$$CLOCK_GETTIME_TEST" >.featuretest.c
@printf "\nexec: %s\n" "$(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) -lrt .featuretest.c -o .featuretest$(EXEC_SUFFIX)" >>$(BUILD_DETAILS_FILE)
@ { $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) -lrt .featuretest.c -o .featuretest$(EXEC_SUFFIX) >&2 && \
( echo "found."; echo "CLOCK_GETTIME := yes" >>.features.tmp ) || \
( echo "not found."; echo "CLOCK_GETTIME := no" >>.features.tmp ) } \
2>>$(BUILD_DETAILS_FILE) | tee -a $(BUILD_DETAILS_FILE)
@$(DIFF) -q .features.tmp .features >/dev/null 2>&1 && rm .features.tmp || mv .features.tmp .features
@rm -f .featuretest.c .featuretest$(EXEC_SUFFIX)