Re: [RFC PATCH] Add rtc server, rtc-read and rtc-set operations

[Samuel Thibault]

Zhaoming Luo, le mar. 19 nov. 2024 16:54:38 +0800, a ecrit:
> On 11/17/24 9:04 PM, Sergey Bugaev wrote:
> I don't think I need to do anything before exit. However, maybe I need to
> ensure the rtc operations is thread-safe; I haven't done it.

Ah, yes. Since it's not a performance-critical service, you can as well
use ports_manage_port_operations_one_thread instead, and get done with
it :)

> I will do some experiments to see whether two threads setting rtc causes
> data race

It will since cmos access requires two outb calls, but it'll be very
hard to reproduce.

> > > +  The following flags have to be released exactly in this order,
> > > +  otherwise the DS12887 (popular MC146818A clone with integrated
> > > +  battery and quartz) will not reset the oscillator and will not
> > > +  update precisely 500 ms later. You won't find this mentioned in
> > > +  the Dallas Semiconductor data sheets, but who believes data
> > > +  sheets anyway ... -- Markus Kuhn */
> > > +  cmos_write(11, save_control);
> > > +  cmos_write(10, save_freq_select);
> > 
> > Can these writes somehow fail, and if so, can you detect it and report
> > the error? (I've no idea.)
> I think the only way to check is reading rtc between `cmos_write(9,
> tm.tm_year);` and `cmos_write(11, save_control);`; then compare the values
> we just read with the values for setting.

I don't think it is useful to do this. Nowadays RTC is not even a
separate chip, we won't have any issue.

Samuel