[U-Boot] [PATCH 3/9] arm: Move CP15 init out of cpu_init_crit()

[Simon Glass]

Hi Albert,

On Thu, Oct 27, 2011 at 1:05 PM, Albert ARIBAUD
<albert.u.boot at aribaud.net> wrote:
> Hi Simon,
>
> Le 25/10/2011 23:16, Simon Glass a écrit :
>
>>> But please think about what you actually want in start.S. Do you
>>> really want an #ifdef TEGRA2 with a check of a SOC register, followed
>>> by a branch around the cp15_init code?
>>
>> ^^^^
>> This is the bit we need to sort out.
>
> Indeed, but I dont want a '#ifdef TEGRA2'. In the worst case I want a 'if
> (!core_is_avp())' by way of an identification register, and in the best
> case, I just want cp15 to be set unconditionally.

You already have #ifdef TEGRA2 (look at the top of start.S). That is
what I am trying to remove.

How can I call core_is_avp() on an SOC that isn't Tegra? Can you
please write a little code fragment that I should use in start.S, so
that I can understand what is required here.

>
>>>>>> According to ARM, coprocessors 14 and 15 should always be supported
>>>>>> from
>>>>>> ARMv6 up. Are you sure the AVP does not have it? If there is a Tegra
>>>>>> specification available, I'd like to have a look at it.
>>>>>
>>>>> Sorry I meant caches/MMU, etc. I should try doing the CP15 cache/MMU
>>>>> init on the AVP and see what happens.
>>>>
>>>> Please do check this. It may be that you can actually write to it from
>>>> AVP
>>>> even though it has no or not all expected effect; and if that is
>>>> confirmed,
>>>> then you don't have to separate the boot paths any more,
>>>
>>> Yes I'm tempted to go with this even if the ARM ARM is silent on the
>>> matter. I will try it out today.
>>
>> Silly me of course it doesn't work - since if the CP15 doesn't have
>> those features then you get undef instruction exception. Please see
>> ^^^ above!
>
> Are you stating a reasoning here or the results of an actual test? What
> causes an undefined instruction exception is the absence of a coprocessor to
> handle the instruction, not the presence of a coprocessor which incidentally
> cannot perform all of what"s being asked.

Yes I did test it - it hangs. Would you like me to spend some time to
debug exactly why? I suspect it is an undef instruction, since
executing cache instructions on an ARM7TDMI is dodgy, but I could
check if it would help. But let's assume for now we can't do that!

Regards,
Simon

>
>> Regards,
>> Simon
>
> Amicalement,
> --
> Albert.
>