Re: [PATCH v4 0/6] SA1100/PXA RTC clean-up

[Robert Jarzmik <robert.jarzmik@free.fr>]

Rob Herring <robh@kernel.org> writes:

>>>>  - you explain in the commit message that from a userland perspective, nothing
>>>>    changes, except that the RTC IP will change, and any dependency on a
>>>
>>> The IP does not change here. rtc0 is still going to be the SA1100 RTC
>>> being registered first. The only change will be the addition of rtc1.
>> For boards which were only using rtc-pxa.c (as mioa701 for example), they relied
>> on the fact that rtc0 == pxa_rtc. Their time is stored in PXA IP. Therefore,
>> each of their hwclock will end up on sa1100-rtc instead of pxa-rtc.
>>
>> So for these boards, ie. for all boards where only rtc-pxa.c was used, the IP
>> addressed changes from a casual userspace perspective.
>
> Okay, so this is the case where the time will be wrong.
>
> I could remove the select of the sa1100-rtc and do an empty function
> for sa1100_rtc_init. This would preserve current behavior.
Please don't. I only ask for a sentence in the commit message.

>>>>    bootloader fidling with RTC should be considered as a source of regression.
>>>
>>> I'm not sure that I follow.
>> Let's talk about how a double boot windows + linux box works.
>> The bootloader ensures that :
>>  - sa1100-rtc holds the number of seconds since the OS start (think jiffies)
>>  - pxa-rtc holds the wall clock time
>>
>> Upon each reboot, sa1100-rtc is checked to see how much time has passed. If an
>> "oustanding number" is detected, for example 10 years, the firmware resets the
>> data partition.
>>
>> Now think what will happen when this change will be commited, upon the first
>> reboot after the linux kernel has change sa1100-rtc time.
>
> That would be bad. But on these platforms, the kernel has been using
> both RTCs right? Presumably on platforms only using 1 of the RTCs, the
> bootloader does not touch the RTCs.
No, the kernel has been using only pxa-rtc. The sa1100-rtc is not used, and yet
it accounts the passed time in it.

On platforms where all the OSes use only 1 RTC, the bootloader only touches one
RTC, that's correct. Or said differently : the bootloader touches the union of
all the RTCs the OSes it launches do touch.

>> All of this to say maintainers should be forwarned at least. After that, up to
>> them to react.

Cheers.

-- 
Robert