rtc-opal: Fix handling of firmware error codes, prevent busy loops

[Michael Ellerman]

On Tue, 2016-08-02 at 01:50:16 UTC, Stewart Smith wrote:
> According to the OPAL docs:
> https://github.com/open-power/skiboot/blob/skiboot-5.2.5/doc/opal-api/opal-rtc-read-3.txt
> https://github.com/open-power/skiboot/blob/skiboot-5.2.5/doc/opal-api/opal-rtc-write-4.txt
> OPAL_HARDWARE may be returned from OPAL_RTC_READ or OPAL_RTC_WRITE and this
> indicates either a transient or permanent error.
> 
> Prior to this patch, Linux was not dealing with OPAL_HARDWARE being a
> permanent error particularly well, in that you could end up in a busy
> loop.
> 
> This was not too hard to trigger on an AMI BMC based OpenPOWER machine
> doing a continuous "ipmitool mc reset cold" to the BMC, the result of
> that being that we'd get stuck in an infinite loop in opal_get_rtc_time.
> 
> We now retry a few times before returning the error higher up the stack.
> 
> Cc: stable at vger.kernel.org
> Signed-off-by: Stewart Smith <stewart at linux.vnet.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/5b8b58063029f02da573120ef4dc90

cheers