Nico Huber has submitted this change and it was merged. ( https://review.coreboot.org/19391 )
Change subject: udelay: Use clock_gettime() if available and precise ......................................................................
udelay: Use clock_gettime() if available and precise
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 --- M Makefile M udelay.c 2 files changed, 78 insertions(+), 0 deletions(-)
Approvals: Stefan Reinauer: Looks good to me, approved Philippe Mathieu-Daudé: Looks good to me, but someone else must approve David Hendricks: Looks good to me, approved build bot (Jenkins): Verified
diff --git a/Makefile b/Makefile index 65026da..8b21431 100644 --- a/Makefile +++ b/Makefile @@ -1003,6 +1003,9 @@ # 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) $(LIBFLASHROM_OBJS)
@@ -1299,6 +1302,18 @@ endef export LINUX_I2C_TEST
+define CLOCK_GETTIME_TEST +#include <time.h> + +int main(int argc, char **argv) +{ + struct timespec res; + clock_gettime(CLOCK_REALTIME, &res); + return 0; +} +endef +export CLOCK_GETTIME_TEST + features: compiler @echo "FEATURES := yes" > .features.tmp ifneq ($(NEED_LIBFTDI), ) @@ -1341,6 +1356,13 @@ @ { $(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)
diff --git a/udelay.c b/udelay.c index 7c6961d..3a44c16 100644 --- a/udelay.c +++ b/udelay.c @@ -21,12 +21,63 @@
#ifndef __LIBPAYLOAD__
+#include <stdbool.h> #include <unistd.h> +#include <errno.h> #include <time.h> #include <sys/time.h> #include <stdlib.h> #include <limits.h> #include "flash.h" + +static bool use_clock_gettime = false; + +#if HAVE_CLOCK_GETTIME == 1 + +#ifdef _POSIX_MONOTONIC_CLOCK +static clockid_t clock_id = CLOCK_MONOTONIC; +#else +static clockid_t clock_id = CLOCK_REALTIME; +#endif + +static void clock_usec_delay(int usecs) +{ + struct timespec now; + clock_gettime(clock_id, &now); + + const long end_nsec = now.tv_nsec + usecs * 1000L; + const struct timespec end = { + end_nsec / (1000 * 1000 * 1000) + now.tv_sec, + end_nsec % (1000 * 1000 * 1000) + }; + do { + clock_gettime(clock_id, &now); + } while (now.tv_sec < end.tv_sec || (now.tv_sec == end.tv_sec && now.tv_nsec < end.tv_nsec)); +} + +static int clock_check_res(void) +{ + struct timespec res; + if (!clock_getres(clock_id, &res)) { + if (res.tv_sec == 0 && res.tv_nsec <= 100) { + msg_pinfo("Using clock_gettime for delay loops (clk_id: %d, resolution: %ldns).\n", + (int)clock_id, res.tv_nsec); + use_clock_gettime = true; + return 1; + } + } else if (clock_id != CLOCK_REALTIME && errno == EINVAL) { + /* Try again with CLOCK_REALTIME. */ + clock_id = CLOCK_REALTIME; + return clock_check_res(); + } + return 0; +} +#else + +static inline void clock_usec_delay(int usecs) {} +static inline int clock_check_res(void) { return 0; } + +#endif /* HAVE_CLOCK_GETTIME == 1 */
/* loops per microsecond */ static unsigned long micro = 1; @@ -87,6 +138,9 @@
void myusec_calibrate_delay(void) { + if (clock_check_res()) + return; + unsigned long count = 1000; unsigned long timeusec, resolution; int i, tries = 0; @@ -189,6 +243,8 @@ /* If the delay is >1 s, use internal_sleep because timing does not need to be so precise. */ if (usecs > 1000000) { internal_sleep(usecs); + } else if (use_clock_gettime) { + clock_usec_delay(usecs); } else { myusec_delay(usecs); }