[U-Boot] [Resend RFC PATCH 1/2] armv8: Fix dcache disable function

[Stephen Warren]

On 10/26/2016 01:54 PM, york sun wrote:
> On 10/26/2016 12:47 PM, Stephen Warren wrote:
>>
>> There are two data structures in ARM U-Boot that describe memory layout:
>>
>> 1) A list of RAM memory regions. U-Boot uses these to know where to
>> relocate itself to (it relocates itself to the top of RAM at boot), and
>> to fill in the /memory node when booting an OS using DT (and other
>> equivalent mechanisms when not using DT.)
>>
>> 2) For AArch64 specifically, there's a memory map table that defines all
>> RAM and MMIO regions, and the translation table attributes required for
>> those regions.
>>
>> Judging by your comments later in the original message, it sounds like
>> it'd be fine to read from these structures during any dcache clean
>> routine provided the table has already been cleaned. That makes using
>> the tables much more tractable:-)
>>
>
> I think we need to benchmark walking through the MMU tables. It can map
> huge amount of memory. For our case, it is more than 16GB. I have been
> reluctant to do so for the size. I am now back testing to revert _this_
> patch, hoping to confirm what I learned from this discussion. After
> that, I will see how long it takes to flush all cached addresses by VA.

Given the existence of the two data structures I mentioned above, I 
don't think we'd ever need to walk the MMU translation tables (assuming 
you mean the data structures U-Boot creates and configures into the 
CPU's MMU), rather than just walking over the tiny number of entries in 
those data structures?