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

[Stewart Smith]

Alexandre Belloni <alexandre.belloni at bootlin.com> writes:
> On 02/08/2016 at 11:50:16 +1000, 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>
>> ---
>>  drivers/rtc/rtc-opal.c | 12 ++++++++++--
>>  1 file changed, 10 insertions(+), 2 deletions(-)
>> 
>
> Just a note to let you know that this patch should have gone through my
> tree but it was not sent to linux-rtc or me.
>
> I guess what happened is that Michael cleaned up the Linux PPC patchwork
> queue.

Apologies for not sending there. My (18 month ago self) bad.

-- 
Stewart Smith
OPAL Architect, IBM.