Re: [PATCH v2 0/8] rtc: enable adjustment of clock offset

From: Joshua Clayton
Date: Tue Jan 26 2016 - 09:56:51 EST


On Monday, January 04, 2016 10:31:18 AM Joshua Clayton wrote:
> Alexandre,
> this is the second version of apatch set to be able to adjust the
> clock on a pcf2123, but with a big addition. I am also proposing
> a couple of new rtc api functions and a new sysfs file.
> Patches 1-5 are very much v2 patches that address All of the
> concerns you had with v1. It is my hope to get them merged without
> too much more trouble.
The rtc _needs_ patches 1-5 in order to use the clock offset
adjustment at all (current upstream code resets it to zero during
device probe, so it doesn't survive a reboot)
Should I split out patches 1-5 to make them easier to review?

> Patches 6-8 are attemping to add a new function to the rtc class
> to adjust the clock rate. I hope I am going about this the right way,
> But here goes.
I am hoping to have some discussion about 6, 7 and 8.
Particularly whether parts per billion is the right unit (I think it is)
and whether "offset" is the best name for the attribute (not as sure).

> A number of rtc devices, such as the NXP pcf2123 include a facility
> to adjust the clock in order to compensate for temperature or a
> crystal, capacitor, etc, that results in the rtc clock not running
> at exactly 32.768 kHz.
> This patchset adds kernel and sysfs hooks to access that ability.
> One datasheet suggests it might be adjusted based on input from
> a temperature sensor. I could also potentially see it being set
> as part of ntp calibration.
> Data sheets I have seen refer to this as a clock offset, and measure it
> in parts per million (ppm), however they often reference ppm to 2 digits
> of precision, which makes integer ppm less than ideal. I use parts per
> billion, which more than covers the precision needed and works nicely
> within 32 bits
> The name "offset" came from the pcf-2123 datasheet and is used by at
> least some other data sheets. I would be happy to use a different term
> if someone else comes up with something more concise.
> Changes since v1:
> - Use the BIT() macro for all register bits
> - Remove unneeded range checks from read/write functions
> - Merge patch 3 (replace magic numbers with defines) into patch 2
> - Add a proper commit message to patch 5, now patch 4
> - Fix a function alignment bug.
> - Move OSC_HAS_STOPPED check into pcf2123_rtc_read_time, and get rid of
> pcf2123_time_valid()
> - Drop patches refactoring pcf2123 sysfs.
> - Add rtc interface and rtc sysfs file for clock offset
> Joshua Clayton (8):
> rtc-pcf2123: define registers and bit macros
> rtc-pcf2123: clean up reads from the chip
> rtc-pcf2123: clean up writes to the rtc chip
> rtc-pcf2123: refactor chip reset into a function
> rtc-pcf2123: avoid resetting the clock if possible
> rtc: Add functions to set and read clock offset
> rtc: implement a sysfs interface for clock offset
> rtc-pcf2123: implement read_offset and set_offset
> drivers/rtc/interface.c | 57 ++++++++++
> drivers/rtc/rtc-pcf2123.c | 271 +++++++++++++++++++++++++++++++++-------------
> drivers/rtc/rtc-sysfs.c | 29 +++++
> include/linux/rtc.h | 4 +
> 4 files changed, 284 insertions(+), 77 deletions(-)
Thanks again,
Joshua Clayton