[U-Boot] [Patch v4 2/5] ARMv8: Adjust MMU setup

[fenghua at phytium.com.cn <fenghua@phytium.com.cn>]

hi York, 

> On 06/10/2014 02:15 AM, Mark Rutland wrote:
>> Hi,
>> 
>> Apologies for the delay in replying.
>> 
>> On Fri, Jun 06, 2014 at 11:14:23PM +0100, York Sun wrote:
>>> On 06/06/2014 01:17 PM, York Sun wrote:
>>>> On 06/06/2014 10:32 AM, Mark Rutland wrote:
>>>>>>> How is TCR_EL2.SH0 (or TCR_EL1.SH*) configured?
>>>>>>> 
>>>>>>> You'll only need to flush the cache if they're configured non shareable.
>>>>>> 
>>>>>> It is configured as non shareable.
>>>>> 
>>>>> Is there any reason not to configure them as inner shareable? That way
>>>>> the MMU will look in the D-cache, and you won't have to spend time
>>>>> flushing them.
>>>>> 
>>>> 
>>>> Mark,
>>>> 
>>>> I appreciate the reminder. I tried on our emulator. With inner share set for TCR
>>>> SH0 bits, u-boot works with the flushing, but doesn't work without flushing. It
>>>> went to exception.
>>>> 
>>>> Can you share more information about the inner share? I need to follow up with
>>>> our designer to confirm.
>>>> 
>>> 
>>> A second thought, do I need to set the first MMU table so DDR is inner shareable?
>> 
>> I assume you mean configuring MAIR_ELx such that the mapping covering
>> DDR is cacheable for the inner shareable domain? If so, yes.
>> 
> 
> Mark,
> 
> I tried both inner share and outer. It doesn't work without flushing the cache.
> I will keep this part of code until I learn otherwise.
> 
> York
> 
The shareability attribute is different with cacheablilty attribute, it means whether the
memory region would be accessed by other processors. If a memory region is configured
as non sharable the access will not be snooped but still can be cached. It is the situation that
current u-boot-armv8 used due to only master processor is active. If secondary processors
also access the same memory region it should be configured as inner-sharable or outer-sharable
otherwise the cache coherence between processors will not be maintained.
The above is what I know. Wish this could help.

David