[PATCH v3 2/2] OMAP: IOMMU: add support to callback during fault handling

[David Cohen]

On Wed, Feb 23, 2011 at 10:09 PM, Sakari Ailus
<sakari.ailus at maxwell.research.nokia.com> wrote:
> Guzman Lugo, Fernando wrote:
>> Hi,
>
> Hi Fernando,
>
>> In OMAP4 the cortex M3 is a double core processor and as each core is
>> running they own version of the RTOS we threat them independently. So
>> our driver which controls the remote processor sees two processor but
>> both use the same iommu hw. When a iommu fault happens, at this
>> moment, it is consider as a faltal error and it is no managed to
>> recover and continue, instead a restart of the processor is needed, if
>> the fault happens in core0 we need to reset core1 too and vice versa.
>> if the iommu would support several user callbacks, we can register the
>> callback which resets core0 and also the callback which resets core1
>> and treat them as totally independent processors. Also we have an
>> error event notifier driver, which is only in charge of notifying
>> error events to userspace, so we would have multiple callbacks we
>> could do this
>
> The original purpose of the patch, as far as I understand, is to allow
> getting useful information for debugging purposes should an iommu fault
> happen.
>
> Also, I'm not sure it's necessarily a good idea to just go and reset
> the M3 cores in case an iommu fault happens --- this is very probably a
> grave bug in the software running on those M3s. It should be fixed
> instead of just hiding it. There will be consequences to host side as
> well, won't there?

That's really a good point. callbacks in this situation are mostly to
debug purpose. Drivers shouldn't rely on that to work properly.

David

>
>> iommu <---- register fault callback for error notify driver
>>
>> instead of
>>
>> iommu <--- register fault callback for remote processor driver
>> <----register fault event for error notify driver.
>>
>> with that, we remove one dependency of the errornotify driver.
>
> I suppose this is not in mainline?
>
> Regards,
>
> --
> Sakari Ailus
> sakari.ailus at maxwell.research.nokia.com
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