Re: [RESEND] powerpc/configs: enable RTC class support

[Vaibhav <vaibhav@linux.vnet.ibm.com>]

On Fri, 2015-07-03 at 16:59 +1000, Michael Ellerman wrote:
> You still haven't told me what happens on a pseries machine when this
is
> applied.

Was finally able to get my hand over a pseries guest lpar today so
dumping the results below. I have aggregated results for each
configuration namely host & guest version; with each with/without the
patch. So in all results for 4 different configurations.

-------------------------
*host-kernel/without patch
-------------------------

Without the patch the hwclock fails with an error message:

[root@tul169p1 ~]# hwclock
hwclock: Timed out waiting for time change.
hwclock: The Hardware Clock registers contain values that are either
invalid (e.g. 50th day of month) or beyond the range we can handle (e.g.
Year 2095).

Debug message of hwclock reveal that hwclock cannot detect any tick in
the RTC clock. This is due to older genrtc driver being used instead of
newer rtc-opal driver.

-------------------------
*host-kernel/with patch
-------------------------

The patch enables the rtc-opal driver by enabling CONFIG_RTC_CLASS. So
the hwclock starts working. Below is the command log:

[root@tul169p1 ~]# hwclock -r
Fri 03 Jul 2015 03:54:31 AM CDT  -0.876949 seconds

--------------------------
*guest-kernel/without patch
---------------------------
Without the patch hwclock still works but uses the legacy generic-rtc.
Below is the output indicating that:

linux-3bot:/ # hwclock -r
Sun Jul  5 21:19:51 2015  -0.885070 seconds

linux-3bot:/ # ls /dev/class/rtc
ls: cannot access /dev/class/rtc: No such file or directory

--------------------------
*guest-kernel/with patch
---------------------------
With the patch, which enables the new rtc_class framework, the legacy
behavior is still used preserved. Below is the output indicating that:
linux-3bot:~ # hwclock -r
Sun Jul  5 21:36:53 2015  -0.704169 seconds

linux-3bot:~ # ls /sys/class/rtc
rtc0

~Vaibhav