[U-Boot] [PATCH 1/2] armv8: add hooks for all cache-wide operations

[Simon Glass]

Hi Stephen,

On 18 October 2016 at 12:58, Stephen Warren <swarren at wwwdotorg.org> wrote:
> On 10/18/2016 10:23 AM, Simon Glass wrote:
>>
>> Hi Stephen,
>>
>> On 17 October 2016 at 15:35, Stephen Warren <swarren at wwwdotorg.org> wrote:
>>>
>>> From: Stephen Warren <swarren at nvidia.com>
>>>
>>> SoC-specific logic may be required for all forms of cache-wide
>>> operations; invalidate and flush of both dcache and icache (note that
>>> only 3 of the 4 possible combinations make sense, since the icache never
>>> contains dirty lines). This patch adds an optional hook for all
>>> implemented cache-wide operations, and renames the one existing hook to
>>> better represent exactly which operation it is implementing. A dummy
>>> no-op implementation of each hook is provided. These dummy
>>> implementations are moved into C code, since there's no need to
>>> implement them in assembly.
>>>
>>> Signed-off-by: Stephen Warren <swarren at nvidia.com>
>>> ---
>>>  arch/arm/cpu/armv8/cache.S                   |  6 ------
>>>  arch/arm/cpu/armv8/cache_v8.c                | 23
>>> ++++++++++++++++++++---
>>>  arch/arm/cpu/armv8/fsl-layerscape/lowlevel.S |  4 ++--
>>>  arch/arm/include/asm/system.h                |  5 ++++-
>>>  arch/arm/mach-tegra/tegra186/cache.c         |  2 +-
>>>  5 files changed, 27 insertions(+), 13 deletions(-)
>>>
>>
>> I think we should have a proper interface for this stuff rather than
>> weak functions. Maybe we need a linker-list approach, or a cache
>> uclass?
>
>
> What's improper about this interface? Presumably we could argue that no
> function in the entire of U-Boot be called by symbol name, which doesn't
> seem useful.
>
> I'm not sure exactly what you envisage by a linker-list approach. Can you
> provide some background? I understand how the linker can construct list of
> objects/implementations/..., but that doesn't seem useful here since there's
> a known-ahead-of-time single implementation of these functions in a single
> build of U-Boot.

Your own commit messages says that this is SoC-specific. I'm
suggesting that we define an interface (which I think you have already
done with your header file additions), and allow SoCs to implement it
via a linker list.

IMO the cache code in U-Boot is starting to get a bit creaky.

>
> A cache uclass seems like /massive/ overkill, especially since I'd expect
> these very low-level functions to be required well before any higher level
> code like DM/classes/... to be available.

DM is available very early. But it's not clear from your patch when
this code is actually called.

Regards,
Simon