linux-kernel - [PATCH RFC 0/8] Dynamic clock devices

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Date:	Thu, 4 Nov 2010 20:26:34 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-api@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Christoph Lameter <cl@...ux.com>,
	John Stultz <johnstul@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH RFC 0/8] Dynamic clock devices

Okay, here is a work in progress, not well tested, but I would like to
get some feedback whether the direction is good or not.

The first patch introduces clock devices which can appear and
disappear like usb devices (and, I suppose, hot plug PCI but I am not
too sure that what is offered here would really work in that case).
The subsequent patches convert the clock_ and timer_ system calls, one
by one.

The clock_ syscalls are moved into a new file and they call the older
posix functions when needed. The timer_ syscalls stay where they are,
in posix-timers.c, since I did not want to change the fairly involved
timer management code. Eventually, we could remove the posix clock_*
functions for the CLOCK_* ids from posix-timers.c and rework them
using the new dynamic clock api. That would leave just the timer code
in posix-timers.c, as the file name suggests.

I dropped the idea of having user space open a sysfs file in order to
get a reference to a clock, since there are no open/release hooks
within sysfs for drivers (coincidentally, there has been some talk
about this on the lkml recently, but previously Greg KH object to
abusing sysfs as a "clockfs").

Instead, since many clocks (hpet, rtc, ptp, ...) will want to offer a
custom chardev for special advanced functionality, the dynamic clock
layer registers a cdev for the driver, placing its own hooks into the
open/release methods. The driver thus needs to access its private data
via a standard access method (not just by using fp->private_data). If
a driver doesn't want any chardev functions, that is okay, too.

Well, please take a look and let me know what you think.

Thanks,

Richard

Richard Cochran (8):
  Introduce dynamic clock devices
  clock device: convert clock_gettime
  clock device: convert clock_getres
  clock device: convert clock_settime
  clock device: convert timer_create
  clock device: convert timer_delete
  clock device: convert timer_gettime
  clock device: convert timer_settime

 include/linux/clockdevice.h  |  117 +++++++++++++++
 include/linux/posix-timers.h |   23 +++-
 include/linux/time.h         |    2 +
 kernel/posix-timers.c        |   51 +++++--
 kernel/time/Makefile         |    3 +-
 kernel/time/clockdevice.c    |  336 ++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 518 insertions(+), 14 deletions(-)
 create mode 100644 include/linux/clockdevice.h
 create mode 100644 kernel/time/clockdevice.c

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