[U-Boot] "armv7: integrate cache maintenance support" breaks km_kirkwood ethernet

[Aneesh V]

Dear Wolfgang,

On Friday 29 July 2011 06:03 PM, Wolfgang Denk wrote:
> Dear Aneesh,
>
> In message<4E3161ED.5030109 at keymile.com>  Holger Brunck wrote:
>>
>> today I did a rebase of my development branch to current u-boot master. And I
>> saw on our km_kirkwood board that our egiga0 interface isn't working anymore.
>>
>> The CPU is a:
>> SoC:   Kirkwood 88F6281_A0
>>
>> After bisecting the current tree I got:
>>
>> c2dd0d45540397704de9b13287417d21049d34c6 is the first bad commit
>> commit c2dd0d45540397704de9b13287417d21049d34c6
>> Author: Aneesh V<aneesh at ti.com>
>> Date:   Thu Jun 16 23:30:49 2011 +0000
>>
>>      armv7: integrate cache maintenance support
>>
>> And indeed after reverting this commit on current HEAD my board is usable again.
>
> The same is true for iMX27 (and probably other boards / SoCs):
>
> I verified for both the "imx27lite" and "magnesium" boards that above
> patch breaks Ethernet on these iMX27 boards.
>
> Seems we have a bigger problem here...

I had written a small write-up on this earlier today in the below
thread:
http://marc.info/?l=u-boot&m=131193466800729&w=2

I had done extensive testing on the armv7 cache-maintenance APIs by
creating coherency issues and solving them using the APIs. I believe
the problems are due to the APIs not being appropriately used where
they need to be used, also coupled with the fact that dcache_enable()
is now called from board_init_r().

Anyway, I will test my APIs once again on Cortex-A8 and Cortex-A9.

Maybe, I should also write a README with guidelines for correct cache
usage.

Also, I would suggest the following to solve the problem with breaking
boards:
1. Allow boards to define CONFIG_SYS_DCACHE_OFF and/or
2. Instead of calling dcache_enable() from board_init_r() let's call a
new function like dcache_init(). The default implementation of this
function shall do nothing. The real implementation in platform code may
enable or disable d_cache() on a per SoC/board basis.

best regards,
Aneesh