[U-Boot] [RFC] ARM: omap3: Add option to disable errata workarounds.

[Andreas Naumann <dev@andin.de>]

Hi,

>>> It seems that all three ARM errata workarounds done in omap3 board-init
>>> (#454179 #430973 #621766) are solved/not longer needed e.g. in the
>>> AM/DM37xx chips. Other people have noticed this:
>>> http://e2e.ti.com/support/arm/sitara_arm/f/791/t/254742.aspx
>>>
>>> When still applying them (especcially #430973), lots of segmentations
>>> faults and other strange stuff begin to appear.
>
> I read your link the other way round. If the #430973 errata fix is _not_
> applied to r3p2 it gives a lot of segfaults. Unfortunately the thread
> has noc more information on that.

I dont know what bootloader the guy used, but he states that he needs to 
enable the errata fix in the kernel for the segfaults to disappear. I 
found exactly the same: Initially I had no errata fixes configured for 
the kernel, only when I added them the segfaults disappeared.
However they also disappear if I remove the workarounds from kernel as 
well as u-boot, hence this patch.

>>> So as a simple solution I propose adding a config option to remove these
>>> workarounds for boards/silicon that dont need them. Is this sensible or
>>> should there be more automatism?
>>>
>>>
>>> regards,
>>> Andreas
>>>
>>>
>>> PS. Does anybody have the "ARM Core Cortex-A8 (AT400/AT401) errata"
>>> document to make sure my assumption above holds true?
>
> I have rev 20.0 from 13-Apr-10. The three mentioned errata should be
> fixed in r2p1.

> <snip>
>
>> Two remarks:
>>
>> 1. I would prefer the option to be the other way around, i.e. forcing
>> the inclusion of the workaround when defined rather than when not
>> defined; e.g. CONFIG_SYS_CORTEXA8_WORK_AROUND_ERRATA

If we do that, lots of board configs have to be adapted. People who have 
custom configs probably wont notice and loose their apropriate errata 
handling.

>> 2. (if applicable) I would prefer erratum-specific options, e.g.
>> CONFIG_SYS_CORTEXA8_WORK_AROUND_ERRATUM_430973 -- ok, "ERRATA" will be
>> fine too; what I want is easing the search for errata by number.
>
> I join Albert's suggestion. Another solution could be to read the
> silicon revision and enable erratum workarounds on that information. It
> would be a step towards single binary.

So I'd rather do that, but can we map the ARM revision e.g. r2p1 to the 
TI die versions ES1.0, 1.1 and so on? Or can the ARM revision be read 
directly?

cheers,
Andreas