[U-Boot] [PATCH v5 09/11] armv8: ls2080a: Drop early MMU for SPL build

[Marek Vasut]

On 03/07/2017 05:31 AM, york sun wrote:
> On 03/06/2017 07:59 PM, Marek Vasut wrote:
>> On 03/06/2017 06:02 PM, York Sun wrote:
>>> Early MMU improves performance especially on emulators. However, the
>>> early MMU is left enabled after the first stage of SPL boot. Instead
>>> of flushing D-cache and dealing with re-enabling MMU for the second
>>> stage U-Boot, disabling it for SPL build simplifies the process. The
>>> performance penalty is unnoticeable on the real hardware. As of now,
>>> SPL boot is not supported by existing emulators. So this should have
>>> no impact on emulators.
>>>
>>> Signed-off-by: York Sun <york.sun at nxp.com>
>>
>> This looks stupid. Why don't you just keep it enabled between SPL and
>> U-Boot ? That'd be much more logical and sensible ...
>
> Mark,
>
> We are probably the only one using early MMU to speed up execution on
> emulators. I only noticed recently the cache/MMU wasn't enabled for most
> ARMv8 layerscape SoCs for SPL, except LS2080A (which is where we
> started). During recent debug, I learned the process of
> break-before-make process should be strictly followed when changing MMU.

I don't think I understand this part.

> The normal boot part surely creates MMU tables. If the SPL also creates
> MMU table and enables cache, then we need to flush cache and disable MMU
> before the normal boot part begins to run. Instead of dealing all these
> steps just for LS2080A, I figure it would be a lot easier to drop it as
> I proposed in this patch.

But then this is a step back and makes the whole platform slower, right?

> York
>
>>
>>> ---
>>>
>>> Changes in v5: None
>>> Changes in v4: None
>>> Changes in v3:
>>>   Add a patch to drop early MMU setup for LS2080A SPL build.
>>>
>>> Changes in v2: None
>>>
>>>  arch/arm/cpu/armv8/fsl-layerscape/spl.c | 3 ---
>>>  1 file changed, 3 deletions(-)
>>>
>>> diff --git a/arch/arm/cpu/armv8/fsl-layerscape/spl.c b/arch/arm/cpu/armv8/fsl-layerscape/spl.c
>>> index 1dabdbb..73a8680 100644
>>> --- a/arch/arm/cpu/armv8/fsl-layerscape/spl.c
>>> +++ b/arch/arm/cpu/armv8/fsl-layerscape/spl.c
>>> @@ -45,9 +45,6 @@ void board_init_f(ulong dummy)
>>>  {
>>>  	/* Clear global data */
>>>  	memset((void *)gd, 0, sizeof(gd_t));
>>> -#ifdef CONFIG_LS2080A
>>> -	arch_cpu_init();
>>> -#endif
>>>  	board_early_init_f();
>>>  	timer_init();
>>>  #ifdef CONFIG_LS2080A
>>>
>>
>>
>