[flashrom-gerrit] Change in flashrom[staging]: udelay: Use clock_gettime() if available and precise

[Nico Huber (Code Review)]

Hello Stefan Tauner, Philippe Mathieu-Daudé, Stefan Reinauer, David Hendricks, Paul Menzel, build bot (Jenkins),

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/19391

to look at the new patch set (#5).

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 
---
M Makefile
M udelay.c
2 files changed, 78 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/flashrom refs/changes/91/19391/5