Re: [RFC 0/5] add rtc support

[Sascha Hauer <s.hauer@pengutronix.de>]

On Fri, Jul 11, 2014 at 10:12:36AM +0400, Antony Pavlov wrote:
> On Fri, 11 Jul 2014 07:37:38 +0200
> Sascha Hauer <s.hauer@pengutronix.de> wrote:
> 
> > On Thu, Jul 10, 2014 at 12:33:14PM +0400, Antony Pavlov wrote:
> > > This patchseries imports RTC support from linux-3.15.
> > > 
> > > User can use 'hwclock' command to see realtime clock readout.
> > > 
> > > Tested with DS1307.
> > > 
> > > TODOs:
> > > 
> > >  * rtc_set_time() is not realized;
> > >  * ds1307_set_time() is not tested;
> > >  * bcd lib is compiled in even if rtc support is disabled (as linux does);
> > >    we can make it optional;
> > 
> > It's probably not worth it. The linker will throw it away anyway if
> > unused.
> 
> Hmm, I have missed this.
> 
> In this case can we drop I2C_SMBUS Kconfig stuff
> 
> +config I2C_SMBUS
> +	bool
> +
> 
> +obj-$(CONFIG_I2C_SMBUS) += i2c-smbus.o
> 
> from 'add driver for PCA95[357]x, ...' series?
> 
> Anyway CONFIG_I2C_SMBUS has another meaning in linux.
> 
> > 
> > >  * adjust include/linux/rtc.h and include/rtc.h;
> > >  * rtc_unregister() is not realized.
> > 
> > Maybe an environment variable which holds the seconds since epoch would
> > be useful. This way scripts could make use of the current RTC time.
> 
> So you propose to add an option to hwclock command to store RTC readout into variable,
> isn't it?

Yes. This would allow scripts to compare times or to store the current
time in some boot log.

> 
> I have an idea to put epoch offset (number of years into AD to which a zero year value
> in the Hardware Clock refers) into "global.epoch" variable and add corresponding
> Kconfig option for default epoch value.

Does Linux support such a mechanism aswell? How can we make sure Linux
uses the same epoch offset?

Sascha

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