[L] Change in flashrom[main]: udelay: only use OS time for delays, except on DOS

[Peter Marheine (Code Review)]

Attention is currently required from: Anastasia Klimchuk, Brian Norris, Thomas Heijligen.

Hello Anastasia Klimchuk, Brian Norris, Thomas Heijligen, build bot (Jenkins),

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

https://review.coreboot.org/c/flashrom/+/81545?usp=email

to look at the new patch set (#6).

The following approvals got outdated and were removed:
Verified+1 by build bot (Jenkins)

Change subject: udelay: only use OS time for delays, except on DOS
......................................................................

udelay: only use OS time for delays, except on DOS

As proposed on the mailing list ("RFC: remove the calibrated delay
loop"), this removes the calibrated delay loop and uses OS-based timing
functions for all delays because the calibrated delay loop can delay for
shorter times than intended.

When sleeping this now uses nanosleep() if available, and otherwise
usleep(). When busy-looping, it uses clock_gettime() with
CLOCK_MONOTONIC or CLOCK_REALTIME depending on availability, and
gettimeofday() otherwise.

The calibrated delay loop is retained for DOS only, because timer
resolution on DJGPP is only about 50 milliseconds. Since typical delays
in flashrom are around 10 microseconds, using OS timing there would
regress performance by around 500x. The old implementation is reused
with some branches removed based on the knowledge that timer resolution
will not be better than about 50 milliseconds.

Tested by reading and writing flash on several Intel and AMD systems:

* Lenovo P920 (Intel C620, read/verify only)
 * "nissa" chromebook (Intel Alder Lake-N)
 * "zork" chromebook (AMD Zen+)

Signed-off-by: Peter Marheine 
Change-Id: I7ac5450d194a475143698d65d64d8bcd2fd25e3f
---
M Makefile
M include/programmer.h
M libflashrom.c
M meson.build
M tests/meson.build
M tests/tests.c
M tests/tests.h
A tests/udelay.c
M udelay.c
A udelay_dos.c
10 files changed, 261 insertions(+), 172 deletions(-)

git pull ssh://review.coreboot.org:29418/flashrom refs/changes/45/81545/6