tree f61a16e60f193b5e3f13a377a81d1308b1b4f0ad
parent 2d62572d1dd0c37eb626fd8faa17b26690f20b15
author Nico Huber <nico.h@gmx.de> 1352148393 +0100
committer Nico Huber <nico.h@gmx.de> 1498130055 +0000

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>