[U-Boot] [PATCH v2 35/40] ARM: Implement non-cached memory support

[Simon Glass]

Hi Stephen,

On 24 October 2014 13:11, Stephen Warren <swarren at wwwdotorg.org> wrote:
> On 08/26/2014 09:34 AM, Thierry Reding wrote:
>>
>> From: Thierry Reding <treding at nvidia.com>
>>
>> Implement an API that can be used by drivers to allocate memory from a
>> pool that is mapped uncached. This is useful if drivers would otherwise
>> need to do extensive cache maintenance (or explicitly maintaining the
>> cache isn't safe).
>>
>> The API is protected using the new CONFIG_SYS_NONCACHED_MEMORY setting.
>> Boards can set this to the size to be used for the non-cached area. The
>> area will typically be right below the malloc() area, but architectures
>> should take care of aligning the beginning and end of the area to honor
>> any mapping restrictions. Architectures must also ensure that mappings
>> established for this area do not overlap with the malloc() area (which
>> should remain cached for improved performance).
>>
>> While the API is currently only implemented for ARM v7, it should be
>> generic enough to allow other architectures to implement it as well.
>
>
>> diff --git a/arch/arm/lib/cache.c b/arch/arm/lib/cache.c
>
>
>> +void noncached_init(void)
>
> ...
>>
>> +       mmu_set_region_dcache_behaviour(noncached_start, size,
>> DCACHE_OFF);
>> +}
>
>
> If I build with:
>
> #define CONFIG_SYS_DCACHE_OFF
> #define CONFIG_SYS_ICACHE_OFF
>
> ... then mmu_set_region_dcache_behaviour() doesn't exist (or at least isn't
> linked in) on Jetson TK1 at least.

I see that too. If you #undef CONFIG_SYS_NONCACHED_MEMORY then the
problem goes away. There is a warning in the network driver in this
case but it is not important.

A better solution is probably an #ifdef around the call you mention.
It minimised code changes when cache is on/off which is probably a
good thing.

Regards
Simon