[U-Boot] [RFC][PATCH 17/19] arm cp15: setup mmu and enable dcache

[Heiko Schocher]

Hello Nick,

Nick Thompson wrote:
> On 30/07/10 10:32, Heiko Schocher wrote:
>> Nick Thompson wrote:
>>> On 29/07/10 11:45, Heiko Schocher wrote:
>>>> +	     i++) {
>>>> +		page_table[i] = i << 20 | (3 << 10) | 0x1e;
>>> These numbers ought to be defines, no?
>>>
>>> The 0x1e will not work on da8xx as the data cache is broken. The d-cache can
>>> still be used in write back mode, so the value 0x1a should be used. It would
> 
> Here, I should have said write-thru' can still be used...
> 
>>> be good to have symbols to define the caching modes: none, wr-thru', wr-back
>>> or some such, similar to Linux.
>> Ah, Ok, good hint!
>>
>> What with:
>>
>> if !defined(CONFIG_SYS_ARM_CACHE_SETUP)
>> #define CONFIG_SYS_ARM_CACHE_SETUP	0x1e
>> #endif
>>
>> 		page_table[i] = i << 20 | (3 << 10) | CONFIG_SYS_ARM_CACHE_SETUP;
>>
>> So boards/architectures can define there own values?
> 
> How about:
> 
> #if defined(CONFIG_SYS_ARM_CACHE_WRITETHROUGH)
> #define CACHE_SETUP	0x1a
> #else
> #define CACHE_SETUP	0x1e
> #endif
> 
> 		page_table[i] = i << 20 | (3 << 10) | CACHE_SETUP;
> 
> This would avoid people having to look up the appropriate value(s).

Ok, I am fine with that too.

> This follows the Linux model, but there the symbol CPU_CACHE_WRITETHROUGH
> is used. Ideally, I would suggest we use the CPU form as well, but it
> would imply an effect beyond ARM.

I vote for CONFIG_SYS_ARM_CACHE_WRITETHROUGH

bye,
Heiko
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