[rtc-linux] Re: [PATCH 2/2] doc: dt: add documentation for alphascale,asm9260-rtc

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

On 02/02/2016 at 09:46:02 +0100, Oleksij Rempel wrote :
> Am 01.02.2016 um 16:55 schrieb Alexandre Belloni:
> > On 01/02/2016 at 09:27:50 -0600, Rob Herring wrote :
> >> On Fri, Jan 29, 2016 at 09:40:02AM +0100, Oleksij Rempel wrote:
> >>> Document Alphascale asm9260 RTC bindings
> >>>
> >>> Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
> >>> ---
> >>>  .../bindings/rtc/alphascale,asm9260-rtc.txt        | 25 ++++++++++++++++++++++
> >>>  1 file changed, 25 insertions(+)
> >>>  create mode 100644 Documentation/devicetree/bindings/rtc/alphascale,asm9260-rtc.txt
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/rtc/alphascale,asm9260-rtc.txt b/Documentation/devicetree/bindings/rtc/alphascale,asm9260-rtc.txt
> >>> new file mode 100644
> >>> index 0000000..2c0ff3c
> >>> --- /dev/null
> >>> +++ b/Documentation/devicetree/bindings/rtc/alphascale,asm9260-rtc.txt
> >>> @@ -0,0 +1,25 @@
> >>> +* Alphascale asm9260 SoC Real Time Clock
> >>> +
> >>> +Required properties:
> >>> +- compatible: Should be "alphascale,asm9260-rtc"
> >>> +- reg: Physical base address of the controller and length
> >>> +       of memory mapped region.
> >>> +- interrupts: IRQ line for the RTC.
> >>> +- clocks: Reference to the clock entry.
> >>> +- clock-names: should contain:
> >>> +  * "ahb" for the SoC RTC clock
> >>> +
> >>> +Optional:
> >>> +- calibration: calibration value for 1 sec period.
> >>> +		Max value for forward calibration is 0x1ffff (131071),
> >>> +		Min value for backward calibration is 0xfffe0001 (-131071).
> >>
> >> This should be prefixed with 'alphascale,'
> >>
> >> How is this value determined?
> >>
> > 
> > I think this should stay in userspace, see that series:
> > https://groups.google.com/forum/#!topic/rtc-linux/HGQqiHnMiuw
> > 
> > It quite often depends on environmental things like temperature so it may be updated at runtime.
> > 
> 
> I partially agree. IMO default configuration should work properly by
> 20C. My devkit provide terrible results without default offset.
> 

I'm not against having a sane default. What I would do is set a default
hardcoded value from the driver at the time the RTC is reset (that is: it
has never been set yet) then let the user adjust that calibration
through sysfs.



-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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