This file seeks to explain the nuances in various delays;
many driver writers are not necessarily familiar with the
various kernel timers, their shortfalls, and quirks. When
faced with
ndelay, udelay, mdelay, usleep_range, msleep, and msleep_interrubtible
the question "How do I just wait 1 ms for my hardware to
latch?" has the non-intuitive "best" answer:
usleep_range(1000,1500)
This patch is followed by a series of checkpatch additions
that seek to help kernel hackers pick the best delay.
Signed-off-by: Patrick Pannuto <ppannuto@codeaurora.org>
Cc: apw@canonical.com
Cc: corbet@lwn.net
Cc: arjan@linux.intel.com
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <1280786467-26999-3-git-send-email-ppannuto@codeaurora.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
We should only build hpet_example on x86[-64], where it is implemented.
It can cause build errors on other architectures.
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Documentation/timers/hpet_example.c: fcntl.h is included more than once.
Documentation/timers/hpet_example.c: signal.h is included more than once.
Signed-off-by: Andrea Gelmini <andrea.gelmini@gelma.net>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Documentation/timers/hpet.txt:
Expose example and tool source files in the Documentation/timers/ directory in
their own files instead of being buried (almost hidden) in readme/txt files.
This should help to prevent bitrot.
This will make them more visible/usable to users who may need
to use them, to developers who may need to test with them, and
to anyone who would fix/update them if they were more visible.
Also, if any of these possibly should not be in the kernel tree at
all, it will be clearer that they are here and we can discuss if
they should be removed.
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
That URL is out of date. Update it.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Matt LaPlante <kernel1@cyberdogtech.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: WANG Cong <amwang@redhat.com>
Acked-by: Matt LaPlante <kernel@cyberdogtech.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Minor /dev/hpet updates and bugfixes:
* Remove dead code, mostly remnants of an incomplete/unusable
kernel interface ... noted when addressing "sparse" warnings:
+ hpet_unregister() and a routine it calls
+ hpet_task and all references, including hpet_task_lock
+ hpet_data.hd_flags (and HPET_DATA_PLATFORM)
* Correct and improve boot message:
+ displays *counter* (shared between comparators) bit width,
not *timer* bit widths (which are often mixed)
+ relabel "timers" as "comparators"; this is less confusing,
they are not independent like normal timers are (sigh)
+ display MHz not Hz; it's never less than 10 MHz.
* Tighten and correct the userspace interface code
+ don't accidentally program comparators in 64-bit mode using
32-bit values ... always force comparators into 32-bit mode
+ provide the correct bit definition flagging comparators with
periodic capability ... the ABI is unchanged
* Update Documentation/hpet.txt
+ be more correct and current
+ expand description a bit
+ don't mention that now-gone kernel interface
Plus, add a FIXME comment for something that could cause big trouble
on systems with more capable HPETs than at least Intel seems to ship.
It seems that few folk use this userspace interface; it's not very
usable given the general lack of HPET IRQ routing. I'm told that
the only real point of it any more is to mmap for fast timestamps;
IMO that's handled better through the gettimeofday() vsyscall.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
We have two directories with timer related information in
Documentation/: hrtimers/ and hrtimer/. timer_stats are not restricted
to hrtimers. Move all those files into Documentation/timers where we
can pile up other timer related docs as well.
Pointed-out-by: Randy Dunlap <randy@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
